Taxonomy of Epimedium (Berberidaceae) with special reference to Chinese species.

Epimedii Herba is a commonly used traditional Chinese herbal medicine. Five Epimedium species are included in Chinese Pharmacopoeia and most species of Epimedium are used as Epimedii Herba in practical application. However, as the largest herbaceous genus of the Berberidaceae, Epimedium has many taxonomic controversies which hinder the effective use of Epimedii Herba. This paper reviewed the taxonomic research related to Epimedium, including taxonomic history, taxonomic values of morphological characters, species and distribution, infra-genera taxonomic system and the taxonomic research of Chinese Epimedium. For instance, we recognized Epimedium wushanense and clarified that the species, as described in Flora Reipublicae Popularis Sinicae and Flora of China, actually includes four Epimedium species similar in leaflet shape. In general, it was recognized here that Epimedium comprises 62 species, of which 52 species are distributed in China. For Chinese Epimedium species with the most taxonomic problems, the taxonomic research on the taxa was reviewed and the newest species key was proposed along with proposals for those taxonomic problems needing further resolution. This review is of great implication for the identification, exploration and utilization of Epimedii Herba.

Introduction

Epimedium L. is the largest herbaceous genus of the Berberidaceae with its distribution centre and diversity centre in China. Epimedium plants have been used as Chinese herbal medicines for more than 2000 years. Five Epimedium species, E. sagittatum Maxim., E. pubescens Maxim., E. brevicornu Maxim., E. koreanum Nakai and E. wushanense T. S. Ying, are included in Chinese Pharmacopoeia (Chinese Pharmacopoeia Commission, 2020). Guo et al. (2003) estimated that more than 20 Epimedium species might be used as Epimedii Herba in practical applications. At present, almost species of Epimedium with active ingredients (such as total flavonoids, epimedin A, epimedin B, epimedin C, and icariin) are used as Epimedii Herba. Epimedii Herba has been identified as having good curative effects for sexual dysfunction, osteoporosis, cardiovascular diseases, menstrual irregularity, asthma, chronic nephritis, cancer, decreased immunity and so on (Ma et al., 2011, Jiang et al., 2015, Indran et al., 2016, Tan et al., 2016, Xi et al., 2018). There are dozens of variants of medicines with Epimedii Herba as raw materials (Yu et al., 2018).

Although having great commercial prospects, Epimedium plants have abundant morphological variations and relatively more taxonomic controversies, which lead to the confusion in the use of Epimedii Herba and influence the research and development of the taxon. For instance, Guo et al. (2007) proposed that E. wushanense was a species with similar leaf shapes and various flower characters. Zhang et al. (2014) recognized E. wushanense and clarified that the species, described in Flora Reipublicae Popularis Sinicae (Ying, 2001) and Flora of China (Ying, Boufford, & Brach, 2011), includes four Epimedium species similar in leaflet shape. Xu et al. (2016) reported two new distribution localities of E. epsteinii Stearn. In contrast, we found that the species distributed at the two localities were E. leptorrhizum Stearn, which obviously differed from E. epsteini in terms of foliar and flower characters. In the present paper, we systematically reviewed the taxonomic studies of Epimedium. The history of taxonomic research and taxonomic values of morphological characters of Epimedium were analyzed and discussed. Phylogenetic research of Epimedium was sorted out and further research focus was proposed. As Chinese Epimedium had many taxonomic confusiones, the progress in taxonomy of Chinese Epimedium was reviewed and the newest species key was proposed along with proposals for those taxonomic problems needing further resolution. This review is meaningful for the taxonomic studies of Epimedium and the plant origin identification of Epimedii Herba, as well as for the exploration and utilization of the herbal medicines.

History of taxonomic research on Epimedium species

Linnaeus (1753) established Epimedium and named the first species of the genus, E. alpinum L., which is distributed in the Balkan peninsula and in the southern valleys of the Alps. Morren and Decaisne (1834) published the first monograph of Epimedium in which the genus was recognized with seven species and in which the Epimedium species from Japan and western Asian were introduced for the first time (Table 1). In their monograph, Epimedium was divided into two sections: sect. Macroceras C. Morren & Decne. and sect. Microeras C. Morren & Decne. Sect. Macroceras included three Japanese species bearing large flowers and petals with long spurs, E. macranthum C. Morren & Decne, E. violaceum C. Morren & Decne and E. musschianum C. Morren & Decne. Sect. Microeras bore large flowers and short spurred petals, including E. alpinum, E. pubigerum C. Morren & Decne and E. pinnatum Fisch. from the European Mediterranean and E. elatum C. Morren & Decne from Kashmir. In this monograph, the two researchers published two new monotypic genera: Aceranthus C. Morren & Decne was for spurless Japanese species A. diphyllum Graham, while Vancouveria C. Morren & Decne was for V. hexandra C. Morren & Decne from western North America.

Table 1

System of classification proposed by different researchers and number of Epimedium species in different years.

Morren and Decaisne (1834)	Fischer and Meyer (1846)	Baillon (1862)	Franchet (1886)	Komarov (1908)	Stearn (1938)	Stearn (2002)
Sect. Microceras(four species)	Sect. Microceras(three species)	Sect. Microceras(three species)	Subg. Euepimedium(10 species)	Subg. Euepimedium(16 species)	Sect. Rhizophyllum(two species)	Subg. Rhizophyllum(two species)
Sect. Macroceras(three species)	Sect. Macroceras(four species)	Sect. Macroceras(four species)	Sect. Phyllocaulon(eight species)	Sect. Gymnocaulon(three species)	Sect. Phyllocaulon(19 species)	Subg. Epimedium(52 species)
	Sect. Rhizophyllum(one species)	Sect. Dimorphophyllum(two species)	Sect. Gymnocaulon(two species)	Sect. Phyllocaulon(13 species)	Subsect. Monophyllon(four species)	Sect. Diphyllon(43 species)
		Sect. Aceranthus(one species)	Subg. Vancouveria(one species)	Ser. Monophyllam(three species)	Ser. Microcerae(two species)	Ser. Campanularae(four species)
				Ser. Aceranthus(one species)	Ser. Macrocerae(two species)	Ser. Davidianae(10 species)
				Ser. Diphyllonm(seven species)	Subsect. Aceranthus(three species)	Ser. Dolichocerae(16 species)
				Ser. Polyphylla(two species)	Subsect. Diphyllon(10 species)	Ser. Brachycerae(13 species)
				Subg. Vancouveria(three species)	Ser. Dolichocerae(six species)	Sect. Macroceras(six species)
					Ser. Brachycerae(four species)	Sect. Polyphyllon(one species)
					Subsect. Polyphyllon(two species)	Sect. Epimedium(two species)
					Ser. Elongatae(one species)
					Ser. Elatae(one species)
seven species	eight species	10 species	11 species	19 species	21 species	54 species

Fischer and Meyer (1846) published the second monograph of Epimedium. In their monograph, the two botanists recognized eight Epimedium species, accepted the system of Morren and Decaisne (1834) and treated E. pinnatum as a new section of Epimedium, sect. Rhizophyllum Fisch. & C. A. Mey., which differed from other sections of the genus by its inflorescence lacking leaflets (Table 1). In the third monograph of Epimedium, Baillon (1862) retained the three sections of the system of Fischer and Meyer (1846), but renamed sect. Rhizophyllum as sect. Dimorphophyllum Baillon and adjusted the genus Aceranthus as a new section of Epimedium (Table 1). Cosson (1862) published the other species of sect. Rhizophyllum, E. perralderianu Coss., from western North Africa. There had been ten species of Epimedium reported in 1862. Maximowicz (1877) described the first Chinese species of Epimedium. Since then, the rich diversity of Chinese Epimedium became gradually recognised.

Franchet (1886) published the fourth monograph of Epimedium, in which he adjusted Vancouveria as one subgenus of Epimedium, subg. Vancouveria Franch, treated previous Epimedium as other subgenera, subg. Euepimedium Franch. and recognised 11 Epimedium species, including one species of subg. Vancouveria and four species of subg. Euepimedium from China. Furthermore, subg. Euepimedium was divided into two sections, sect. Phyllocaulon Franch. and sect. Gymnocaulon Franch., and sect. Gymnocaulon was the same as sect. Rhizophyllum of the system of Fischer and Meyer (1846) and as sect. Dimorphophyllum of the system of Baillon (1862) (Table 1). Komarov (1908) recognised 19 Epimedium species and proposed the fifth taxonomic system of the genus. Komarov’s (1908) system accepted Franchet’s (1886) classification and further divided sect. Phyllocaulon into four series mainly based on the number of cauline leaves. Ser. Monophyllam Kom. was with one cauline leaf which included E. alpinum and E. pubigerum from the Mediterranean and E. macranthum from Japan. Ser. Aceranthus Kom. bore one cauline leaf with only two leaflets and was same as sect. Aceranthus of Baillon’s (1862) system which had only one species, E. diphyllum. Ser. Diphyllonm Kom. was mainly with two opposite leaves and comprised of seven Chinese species, such as E. pubescens, E. acuminatum Franch. and E. brevicornu. Ser. Polyphylla Kom. was with several alternative leaves which included E. elatum from western Asian and E. elongatum Kom. from China. Furthermore, subg. Vancouveria had been increased to three species in the system (Table 1).

Stearn (1938) published an excellent monograph: Epimedium and Vancouveria (Berberidaceae). In the monograph, subg. Vancouveria was treated as an independent genus Vancouveria, which was consistent with the primary treatment when the first Vancouveria species was recorded (Morren & Decaisne, 1834). Furthermore, Epimedium was divided into two sections, sect. Rhizophyllum and sect. Phyllocaulon. The four series of sect. Phyllocaulon of Komarov’s (1908) system were also adjusted into four sections, three of which were divided into two series based on geographical distribution. So far, 21 Epimedum species were recognised with 13 species distributed in China (Table 1). With his increased knowledge about Epimedium, especially for Chinese Epimedium, Stearn (2002) proposed the most recent classification system of Epimedium, which adjusted the two sections of Stearn’s (1938) system into two subgenera, subg. Rhizophyllum (Fisch. & C. A. Mey.) Stearn and subg. Epimedium. According to its geographical distribution, subg. Epimedium was divided into four sections. Sect. Diphyllum (Kom.) Stearn comprised Epimedium species endemic to China and was divided into four series based on flower characters. In this monograph, 54 Epimedium species were recognised with 44 species distributed in China (Table 1).

Epimedii Herba was first recorded as an aphrodisiac in Shennong’s Herbal Classic published in Chinese Eastern Han Dynasty or earlier (Sun, 2017). The other functions of Epimedii Herba, such as strengthening bones and muscles, treating rheumatism, relieving cough and asthma and so on, had gradually been recognized in Chinese ancient herbal medicine books (Jiao et al., 2017). The distribution regions of Epimedii Herba, Northern Xichuan (Shaanxi), Shangjun (Yuli and Yan’an of Shaanxi, Mashen banner of Inner Mongolia), were firstly described in Collective Notes to Canon of Materia Medica of Chinese Liang Dynasty (Shang & Shang, 1994). More distribution regions of Epimedii Herba were also recorded in Illustrated Classics of Materia Medica of Chinese Song Dynasty (Hu & Wang, 1988), such as Yongkangjun (Dujiangyan, Sichuan), Yizhou (Lanshan, Shandong), Jiangdong (Jiangsu, Zhejiang and Jiangxi), Shaanxi (Shaanxi, Ningxia, Henan and Gansu), Taishan (Tai’an, Shandong), Hanzhong (Hanzhong, Shaanxi) and Huxiang (Wuxing of Zhejiang and Hunan). Furthermore, although having no species concept, Chinese ancient herbalists noted the morphological diversity of Epimedii Herba. For instance, Illustrated Classics of Materia Medica (Shang & Shang, 1994) recorded that Epimedii Herba was with white or purple flowers and defoliate except those from Huxiang which were evergreen. Compendium of Materia Medica of Chinese Ming Dynasty (Wang, 1999) described that each stem of Epimedii Herba bore one branch with three leaves, while Materia Medica Chongyuan of Chinese Qing Dynasty (Zhang & Wu, 2011) recorded that each stem of the herb bore three branches with three leaves.

As the first Chinese botanist who systematically researched Epimedium, Ying (1975) reviewed Chinese Epimedium, recognising China as possessing 13 Epimedium species with two new species, and treating E. membranceum K. Mey. as a synonym of E. davidii Franch. and E. fargesii Franch. as an insufficiently known species. Subsequent taxonomic progress had led to the publication of more than 40 Epimedium species endemic to China. Flora and illustrated handbooks about Chinese Epimedium have been gradually published, including Flora Reipublicae Popularis Sinicae (Ying, 2001), Flora of China (Ying, Boufford, & Branch, 2011) and the Genus Epimedium of China in Colour (He, 2014). Epimedium has relatively abundant variations of inter- and infra- species and many new Chinese species have been published over the past 40 years, which has brought about new taxonomic questions on Chinese Epimedium. Researchers have carried out taxonomic revisions on Chinese taxa based on morphological and molecular phylogenetic data (Zhang et al., 2011, Zhang et al., 2014a, Zhang et al., 2014b, Zhang et al., 2015a, Zhang et al., 2015b, He, 2014, Liu et al., 2017a, Liu et al., 2017b).

Taxonomic values of morphological characters of Epimedium

Rhizome

Epimedium is a genus of perennial woodland herbs. The morphological characters of rhizome, foliage, inflorescence and flowers are often used to discriminate different Epimedium species. The form of the rhizome, i.e. the degree of elongation and thickness, is relatively stable for each Epimedium species. For example, E. fangii Stearn, E. pauciflorum K.C. Yen and E. perralderianum Coss. have long-creeping and thread-like rhizomes, 1–3 mm in diameter. In contrast, E. diphyllum has short-creeping rhizomes with a diameter of 3–5 mm. Furthermore, the rhizomes of E. wushanense, E. sagittatum and E. borealiguizhouense S. Z. He & Y. K. Yang are usually stouter and more compact and are sometimes more than 1 cm thick.

Stem

Although the stem of Epimedium is terete, wiry, and shows little variation, its indumentum is specific for some Epimedium species. For instance, the stem of E. baojingense Q. L. Chen & B. M. Yang has dark yellow pubescent hairs, while that of E. glandulosopilosum H. R. Liang has multi-cellular glandular hairs and golden-yellow villi.

Foliage

The foliage of Epimedium is so characteristic that the genus may be recognised by its foliage alone (Stearn, 2002). The number of leaflets, the number of leaves on the flowering stem and the morphology of leaflets are important taxonomic characters of Epimedium. For the number of leaflets, E. elachyphyllum Stearn and E. muhuangense S. Z. He & Y. Y. Wang are the only two species in Epimedium which have leaves consisting of a single leaflet. E. perralderianum and most species of sect. Diphyllon (Kom.) Stearn usually bear trifoliolate leaves. E. diphyllon has an unusual modification of the trifoliolate leaf, showing that the terminal leaflet is suppressed and its leaf consists of two lateral leaflets. E. davidii has 5- or 3-foliolate leaves while E. ecalcaratum G. Y. Zhong bears leaves with three, five, or seven leaflets. E. brevicornu, E. xichangense Y. J. Zhang, E. koreanum, E. sempervirens Nakai ex F. Maek., E. alpinum, E. pubigerum and E. pinnatum usually have biternate leaf with nine leaflets. E. elatum bears ternately compound leaves with the larger leaves having 50 or more leaflets. Stearn (2002) proposed that the leaves of Epimedium might have evolved from compound to simple, which is contrary to the hypothesis on the evolution direction of the leaflet number of Epimedium suggested by Ying (2002). The evolution direction of the number of leaflets needs further research and the future system of the genus may be revised to some extent based on the leaflet number.

The number of leaves on the flowering stem has been used in identifying the Epimedium species and infra-genera grouping of the genus (Fischer von and Meyer, 1846, Baillon, 1862, Franchet, 1886, Komarov, 1908, Stearn, 1938, Stearn, 2002). In the updated system of Epimedium (Stearn, 2002), subg. Rhizophyllum has no leaves on the flowering stem, while subg. Epimedium has one, two, three or even up to eight stem leaves. For four sections of subg. Epimedium, sect. Macroceras and sect. Epimedium have one leaf borne on the flowering stem. Sect. Diphyllon often has two stem leaves or sometimes three leaves (E. elongatum) and sometimes one leaf (E. leptorrhizum). Sect. Polyphyllum (Kom.) Stearn comprises only E. elatum, with three to eight ternately compound stem leaves.

The morphology of leaflets, such as shape and indumentum, is usually used to classify Epimedium species. The leaflet shape of Epimedium ranges from nearly orbicular, broadly ovate, ovate, narrowly ovate, lanceolate, to narrowly lanceloate. The base of leaflets is usually cordate with rounded, acute or acuminate basal lobes, except that of E. truncatum H. R. Liang which has almost truncated basal lobes (Fig. 1A–F). Although some Epimedium species have variations in leaflet shape, the leaflet shape is relatively stable for every Epimedium species and can be used for classification of the genus. The adaxial surface of the leaflet of Epimedium is always glabrous except for E. dolichostemon Stearn, E. diphyllon and E. pinnatum. The abaxial surface has many kinds of indumentum or glabrous types. Similar to leaflet shape, the indumentum of the leaflet is characteristic for different Epimedium species and some species have several indumentum types (Zhang et al., 2011, Zhang et al., 2015b, Xu et al., 2013, Liu et al., 2017b). For instance, the adaxial surface of leaflets of E. dolichostemon is glabrous or pubescent, the indumentum on the abaxial surface of the leaflets of E. borealiguizhouense varies from densely strigose to densely pubescent, to lanose and to glabrous (Zhang et al., 2015b).

Fig. 1

Leaf shape in E. platypetalum (A), E. enshiense (B), E. fangii (C), E. sagittatum (D), E. borealiguizhouense (E), E. truncatum (F) and inflorescence of E. pauciflorum (G), E. acuminatum (H), E. mikinorii (I), E. elachyphyllum (J) and E. sagittatum (K–L). Scale bar = 2 cm.

Inflorescence

Epimedium has two kinds of inflorescence, raceme (Fig. 1G) and panicle (Fig. 1H–L). Some species, for example E. pauciflorum, E. platypetalum K. Mey., E. franchetii Stearn, have stable raceme. For the Epimedium species with panicle, the inflorescences of some species have one-flowered upper pedicels and several-flowered lower peduncles (e.g. E. mikinorii Stearn, E. acuminatum, E. elachyphyllum), which may be a simple raceme in younger plants or, in the worst case, for some of the species (e.g. E. acuminatum, E. elachyphyllum). Those of other species fully consist of several-flowered peduncles (e.g. E. sagittatum), whose flower number of peduncle and the width of inflorescence vary among different species and even among different populations of the same species. In fact, the inflorescence of Epimedium is an inexact indefinite inflorescence. Although the inflorescence blooms from bottom to top on the whole, the top flower of each peduncle of the inflorescence always blooms earlier than the preceding lower two flowers.

Flower

Flower characters of Epimedium, such as flower dimension, petal type, the form and relative size of the inner sepals and petals, are mostly stable and specific for every species, which have important taxonomic values for species identification (Fig. 2A–P). Researchers also used these flower characters for classifying infra-genera groups (Morren and Decaisne, 1834, Fischer von and Meyer, 1846, Stearn, 1938, Stearn, 2002). In the updated system of Epimedium (Stearn, 2002), sect. Diphyllon was divided into four series based on flower characters, especially on petal characters. Series Campanulatae Stearn has small campanulate flowers whose petals are flat or with a slight nectarial swelling at the base (Fig. 2A–B). Series Davidianae Stearn has large flowers with the petal possessing an elongated curved spur and a basal lamina (Fig. 2C–F). Series Dolichocerae Stearn also has large flowers whose petal bears long spurs without basal lamina (Fig. 2G–I). Series Brachycerae Stearn has usually 1–4 mm long, short-spur or slipper-shaped petals, which are much shorter than the inner sepal (Fig. 2J–P). Stearn, 2002, Ying, 2002 proposed two different petal evolution routes of Epimedium, both which considered that the Epimedium species with flat petals or with a slight nectarial swelling at the base were the most primitive taxa of the genus (Fig. 2A–B). However, Stearn (2002) considered that Epimedium species evolved from the most primitive petals to long-spur petals with basal lamina (Fig. 2C–F), to long-spur petals without basal lamina (Fig. 2G–I), and finally into short-spur or slipper-shaped petals (Fig. 2J–P), all of which is contrary to the hypothesis proposed by Ying (2002).

Fig. 2

Flowers of E. campanulatum (A), E. reticulatum (B), E. flavum (C), E. hunanense (D), E. pauciflorum (E), E. mikinorii (F), E. acuminatum (G–I), E. fargesii (J), E. dolichostemon (K), E. elachyphyllum (L), E. pubescens (M), E. stellulatum (N), E. sagittatum (O–P). Scale bar = 5 mm.

The flower colour of Epimedium, including that of inner sepal, petal, anther and filament, is relatively stable and often used to identify different species of the genus. However, the flower colour varies in some Epimedium species, although the character is relatively stable within populations. For example, E. acuminatum has yellow and purple flowers, while E. acuminatum, E. pubescens and E. sagittatum have both yellow and green anthers (Zhang et al., 2011, Xu et al., 2019) (Fig. 2G–I, O–P). In addition, the stamens of Epimedium species usually have 1–2 mm long filaments. However, E. fargesii, E. qingchengshanense G. Y. Zhong & B. L. Guo and E. dolichostemon have 4–5 mm long filaments, which make their stamens obviously protrude from the flowers and are a very stable and interesting taxonomic character (Fig. 2J–K).

Capsule

The morphological characters of their capsules have certain taxonomic values. For instance, E. sagittatum, E. myrianthum, E. pubescens, E. stellulatum and E. brevicornu have about 1 cm long capsules, while E. acuminatum, E. franchetii, E. lishichenii and E. membranceum have 2–2.5 cm long capsules. However, the fruit period of Epimedium is relatively short and the capsules burst and fall off when they are ripe. Therefore, many Epimedium herbaria have no capsule and many Epimedium species lack descriptions about their capsules, which affects the application of these characters in classical taxonomy of Epimedium.

Species and distribution of Epimedium

Epimedium is the largest herbaceous genus of Berberidaceae. In the present paper, we reviewed Epimedium and preliminarily recognised that the genus comprises about 62 species (Table 2). As an Old World genus, Epimedium is distributed disjunctively and very unevenly in woodlands or scrubs in the Mediterranean region, western Asia and eastern Asia (Fig. 3). According to Stearn’s system (2002), subg. Rhizophyllum consists of E. perralderianum endemic to Algeria and E. pinnatum endemic to Caucasia. Subgenus Epimedium comprises four sections. Section Epimedium is with E. alpinum in the Alps and the Balkan region and E. pubigerum from Caucasia. Section Polyphyllon contains only one species, E. elatum, which is limited to western Himalaya. Section Macroceras includes six species distributed in Japan, Korea, north-eastern China and Far Eastern Russia. Section Diphyllon possesses about 51 species in central-southeastern China.

Table 2

Species list of Epimedium, including Latin name, distribution region and journal and year in which each species was published.

No.	Latin names	Distribution regions	Journals	Year
Subgen. Epimedium
Sect. Diphyllon (Kom.) Stearn (all endemic to China)
Ser. Campanulatae Stearn
1	E. campanulatum Ogisui	Sichuan	Kew Bull.	1996
2	E. platypetalum K. I. Mey	Sichuan, Shaanxi	Repert. Spec. Nov. Regni Veg. Beih.	1922
3	E. ecalcaratum G. Y. Zhong	Sichuan	Acta Phytotax. Sin.	1991
4	E. reticulatum C. Y. Yu	Sichuan	Acta Phytotax. Sin.	1987
Ser. Davidianae Stearn
5	E. davidii Franch.	Sichuan	Nouv. Arch. Mus. Hist. Nat.	1886
6	E. fangii Stearn	Sichuan	Curtis’s Bot. Mag.	1995
7	E. flavum Stearn	Sichuan	Curtis’s Bot. Mag.	1995
8	E. latisepalum Stearn	Sichuan	Kew Mag.	1993
9	E. ogisui Stearn	Sichuan	Kew Mag.	1993
10	E. xichangense Y. J. Zhang	Sichuan	Phytotaxa	2016
11	E. pauciflorum K. C. Yen	Sichuan	Acta phytotax. Sin.	1993
12	E. shuichengense S. Z. He	Guizhou	Acta Bot. Yunnan.	1996
13	E. wushanense T. S. Ying*	Chongqing, Hubei	Acta Phytotax. Sin.	1975
14	E. epsteinii Stearn	Hunan	Kew Bull.	1997
15	E. hunanense (Hand.-Mazz.) Hand.-Mazz.	Hunan, Guangxi	Symb. Sin.	1931
16	E. shennongjiaense Y. J. Zhang & J. Q. Li	Hubei	Novon	2009
17	E. stearnii Ogisu & Rix	Hubei	Bot. Mag.	2011
18	E. mikinorii Stearn	Hubei	Kew Bull.	1998
19	E. pseudowushanense B. L. Guo	Guangxi, Guizhou	Acta Phytotax. Sin.	2007
Ser. Dolichocerae Stearn
20	E. elongatum Kom.	Sichuan	Trudy Imp. S.-Peterburgsk. Bot. Sada	1908
21	E. membranaceum K. I. Mey	Sichuan, Yunnan	Repert. Spec. Nov. Regni Veg. Beih.	1922
22	E. zhaotongense G. W. Hu	Yunnan	Phytotaxa	2017
23	E. acuminatum Franch.#	Chongqing, Guizhou, Sichuan, Yunnan	Bull. Soc. Bot. France	1886
24	E. jinchengshanense Y. J. Zhang & J. Q. Li	Sichuan	Phytotaxa	2014
25	E. ilicifolium Stearn	Chongqing, Shaanxi	Kew Bull.	1998
26	E. glandulosopilosum H. R. Liang	Chongqing	Acta Phytotax. Sin.	1990
27	E. leptorrhizum Stearn#	Chongqing, Guangdong, Guangxi, Guizhou, Hubei, Hunan	J. Bot.	1933
28	E. sutchuenense Franch.	Chongqing, Guizhou, Hubei	J. Bot. (Morot)	1894
29	E. zhushanense K. F. Wu & S. X. Qian	Hubei	Acta Phytotax. Sin.	1985
30	E. enshiense B. L. Guo & P. G. Xiao	Hubei	Acta Phytotax. Sin.	1993
31	E. franchetii Stearn	Hubei	Kew Bull.	1996
32	E. baojingense Q. L. Chen & B. M. Yang	Guizhou, Hunan	Acta Phytotax. Sin.	1982
33	E. lishihchenii Stearn	Jiangxi	Kew Bull.	1997
34	E. yinjiangense M. Y. Sheng & X. J. Tian	Guizhou	Novon	2011
Ser. Brachycerae Stearn
35	E. fargesii Franch.	Chongqing	J. Bot. (Morot)	1894
36	E. qingchengshanense G. Y. Zhong & B. L. Guo	Sichuan	Acta Phytotax. Sin.	2007
37	E. dolichostemon Stearn	Guizhou, Chongqing, Hubei	Kew Bull.	1990
38	E. elachyphyllum Stearn	Guizhou	Guihaia	1994
39	E. muhuangense S. Z. He & Y. Y. Wang	Guizhou	Phytotaxa	2017
40	E. truncatum H. R. Liang	Hunan	Acta Phytotax. Sin.	1990
41	E. pubescens Maxim.*	Chongqing, Gansu, Shaanxi, Sichuan	Bull. Acad. Imp. Sci. Saint-Pétersbourg	1877
42	E. stellulatum Stearn	Hubei	Kew Bull.	1993
43	E. brevicornu Maxim.*	Gansu, Henan, Ningxia, Qinghai, Shanxi, Shaanxi, Sichuan	Trudy Imp. S.-Peterburgsk. Bot. Sada	1889
44	E. sagittatum (Siebold & Zuccarini) Maxim.*	Anhui, Chongqing, Fujian, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangxi, Zhejiang	Mel. Biol. ix.	1876
45	E. myrianthum Stearn#	Hunan	Kew Bull.	1998
46	E. coactum H. R. Liang & W. M. Yan#	Guizhou	Acta Phytotax. Sin.	1990
47	E. borealiguizhouense S. Z. He & Y. K. Yang	Chongqing, Guizhou, Hubei, Hunan	J. Pl. Resourc. Environ.	1993
48	E. multiflorum T. S. Ying	Guizhou	Fl. Reipubl. Popularis Sin.	2001
49	E. jingzhouense G. H. Xia & G. Y. Li	Hunan	Nordic J. Bot.	2009
50	E. pudingense S. Z. He, Y. Y. Wang & B. L. Guo	Guizhou	Ann. Bot. Fenn.	2010
51	E. tianmenshanensis T. Deng, D. G. Zhang & H. Sun	Hunan	Phytotaxa	2015
Sect. Macroceras C. Morren & Decne (from Japan, Korea, Northeast China, Far Eastern Russia)
52	E. koreanum Nakai*	Japan, Korea, China (Jilin, Liaoning) (dispute)	Fl. Sylv. Kor.	1936
53	E. grandiflorum C. Morren	Japan, Korea, China (Jinlin, Liaoning) (dispute)	Hort. Belge	1834
54	E. sempervirens Nakai ex F. Maek.	Japan (Honshu)	Bot. Mag. (Tokyo)	1932
55	E. macrosepalum Stearn	Russia (Far Eastern Area)	J. Linn. Soc., Bot.	1938
56	E. trifoliolatobinatum (Koidz.) Koidz.	Japan (Shikoku)	Acta Phytotax. Geobot.	1939
57	E. diphyllum G. Lodd.	Japan (Kyushu)	Bot. Cab.	1832
Sect. Polyphyllon (Kom.) Stearn (endemic to Kashimir)
58	E. elatum C. Morren & Decne.	Kashimir	Fl. Sylv. Kor.	1936
Sect. Epimedium (from Europe, Caucasus and North Africa)
59	E. alpinum L.	Alps and mountain ranges of the Balkan peninsula	Sp. Pl.	1753
60	E. pubigerum C. Morren & Decne.	Caucasia	Ann. Sci. Nat., Bot.	1834
Subgen. Rhizophyllum (Fisch. & C. A. Mey.) Stearn (from Caucasus and North Africa)
61	E. pinnatum Fisch.	Caucasia	Syst. Nat. [Candolle]	1821
62	E. perralderianum Coss.	Algeria	Bull. Soc. Bot. France	1862

Note: Species with *are included in Chinese Pharmacopoeia (Chinese Pharmacopoeia Commission, 2020) and Species with # are included in Quality Standard of Traditional Chinese Medicine and Ethnic Medicine in Guizhou Province (Guizhou Drug Administration, 2003).

Fig. 3

Global distribution of Epimedium.

China is the diversity centre and distribution centre for Epimedium, probably being the origin of the genus and the only place where the evolution of Epimedium has continued without interruption and where new species may yet be discovered (Stearn, 2002). In this paper, we preliminarily recognised that there are about 52 species of the genus in China (Table 2) and proposed the newest key to Chinese Epimedium. Among the 52 Chinese Epimedium species, E. sagittatum, E. pubescens, E. brevicornu, E. koreanum and E. wushanense were included in Chinese Pharmacopoeia (Chinese Pharmacopoeia Commission, 2020) within which the former four species are designated as the origin species of Epimedii Folium while E. wushanense is designated as the origin species of Epimedii Folium Wushanensis. Four other Epimedium species, E. acuminatum, E. myrianthum, E. coactum and E. leptorrhizum, were included in Quality Standard of Traditional Chinese Medicine and Ethnic Medicine in Guizhou Province (Guizhou Drug Administration, 2003). Except for E. koreanum belonging to sect. Macroceras and distributed in Jilin and Liaoning of China, Japan and Korea, the other 51 Epimedium species constitute sect. Diphyllum, are all endemic to China and are distributed in the region south of the Qingling Mountains and Huaihe River, north of Xijiang River, east of East China and west of the Hengduan Mountians (24°−36°N, 98°−122°E) (Ying, 2002) (Fig. 4). The diversity of Chinese Epimedium species is most abundant in eastern Sichuan, western Hubei, Chongqing, north-eastern Guizhou and north-western Hunan.

Fig. 4

Distribution of Epimedium in China. Figures indicate the number of Epimedium species in each province.

Phylogenetic research of Epimedium

Epimedium is an endemic genus to the Old World, and the closest relative of the genus is Vancouveria native to western North America (Stearn, 2002). Both Epimedium and Vancouveria are perennial herbs, and usually have compound leaves with a cordate base and clawed petals. In the taxonomic history of Epimedium, Vancouveria had once been treated as one section or subgenus of Epimedium by Baillon, 1862, Franchet, 1886, Komarov, 1908. However, Epimedium has dimerous flowers while Vancouveira has trimerous flowers. Since Stearn (1938) removed subg. Vancouveria from Epimedium and recognised it as an independent genus, the genus Vancouveria has been accepted by taxonomists (Stearn, 2002, Ying, 2002, Kim et al., 2004, Wang et al., 2007). Based on molecular data, the monophyly of Vancoveria, like that of Epimedium, has been verified and the close sister relationship of the two genera has been verified (Kim and Jansen, 1996, Kim and Jansen, 1998, Kim et al., 2004, Sun et al., 2005, Zhang et al., 2007, De Smet et al., 2012, Zhang et al., 2014b, Sun et al., 2018).

Morren and Decaisne (1834) classified Epimedium into two sections, and the taxonomic system of the genus has been revised mainly based on morphological characters (Fischer von and Meyer, 1846, Baillon, 1862, Franchet, 1886, Stearn, 1938, Stearn, 2002). The updated system of Epimedium was established by Stearn (2002), which divided the genus into two subgenera, four sections and four series. In contrast with previous classification systems, Stearn’s system (2002) is relatively reasonable and has been used by researchers. However, the system was only based on leaf and flower morphology, C-banding of chromosomes and geographical distribution. The data of C-banding of chromosomes (Tanaka and Takahashi, 1981, Takahashi, 1989) did not cover all the taxa of the system, as only four Chinese species from ser. Dolichocerae and ser. Brachycerae were studied and the other two series of sect. Diphyllon of China and sect. Polyphyllon were not studied. Furthermore, the results only demonstrated that the chromosome C-banding of Epimedium from the Mediterranean region, China and Japan could be divided into three types, which indicated no differences between the two taxa from the Mediterranean region, sect. Epimedium and subg. Rhizophyllum. Therefore, further research is necessary to investigate the scientific nature of Stearn’s (2002) system.

In order to achieve a natural classification system of Epimedium, researchers conducted phylogenetic studies on the genus using pollen exine ornamentation (Guo, Xiao, & He, 1998), flavonoids (Guo, Pei, & Xiao, 2008) and molecular markers (Nakai et al., 1996, Guo, 1999, Sun et al., 2005, Zhang et al., 2007, De Smet et al., 2012, Zhang et al., 2014b, 2016a). In Stearn’s (2002) system of Epimedium, subg. Rhizophyllum and four sections of subg. Epimedium have, respectively, their relatively unique distribution regions. Molecular phylogenetic analyses, based on internal transcribed spacer (ITS), trnK-matK, atpB-rbcL spacer sequences, random amplified polymorphic DNA (RAPD), PCR-restriction fragment length polymorphism (RFLP) and amplified fragment length polymorphisms (AFLPs), consistently supported subg. Rhizophyllum and four sections of subg. Epimedium as five distinct clades (Nakai et al., 1996, Guo, 1999, Sun et al., 2005, Zhang et al., 2007, De Smet et al., 2012, Zhang et al., 2014b). However, the two subgenera were not well supported and the relationships among five clades were unresolved except for sect. Epimedium as the sister group to sect. Macroceras. For Chinese sect. Diphyllon, although Stearn (2002) divided the section into four series related to flower characters, taxonomic studies only showed some correlation with flower characters based on pollen exine ornamentation (Guo, Xiao, & He, 1998) and flavonoids (Guo, Pei, & Xiao, 2008). Phylogenetic analysis based on AFLP data (Zhang et al., 2014b) divided the section into five well-supported clades related to flower morphology except that five species were either isolated or formed a general polytomy. However, the phylogenetic relationships among the five major clades of sect. Diphyllon were not well-resolved and all the species from the same series did not cluster into one clade. Phylogenetic trees were also constructed based on Epimedium chloroplast genome sequences (Zhang et al., 2016a, Guo et al., 2019). The results showed that E. lishihchenii of ser. Brachycerae clustered with E. pseudowushanense of ser. Dolichocerae, and not with E. acuminatum of ser. Brachycerae. This coincided with the phylogenetic studies based on AFLPs (Zhang et al., 2014b).

Epimedium is a very old taxon and has disjunctive and uneven distribution in the Old World, which includes abundant morphological differentiations. According to the molecular clock approach using rbcL sequences, Zhang et al. (2007) inferred that Epimedium originated between 9.7 and 7.4 million years ago, Chinese sect. Diphyllon originated 0.52 to 0.4 million years ago and the diversification of Chinese sect. Diphyllon was probably a result of frequent range shifts in the Quaternary Period. Ying, 2002, Stearn, 2002 proposed two different petal evolution routes of Epimedium and two different routes for leaflet number evolution of the genus. The results of phylogenetic studies, based on pollen exine ornamentation (Guo, Xiao, & He, 1998), flavonoids (Guo, Pei, & Xiao, 2008) and AFLPs (Zhang et al., 2014b), only supported Stearn’s (2002) hypothesis on the petal evolution routes to some extent. However, the flower evolution route of Epimedium, as well as the foliar evolution of the genus, is unclear. Furthermore, because a natural phylogenetic reconstruction of Epimedium is lacking, the area of origin of the genus, as well as its ways of migration and dispersal in the North Temperate Zone, have not been well explained.

In general, although researchers carried out phylogenetic studies on Epimedium, a natural taxonomic system of Epimedium has not been achieved yet. The taxonomic system of Epimedum needs further improvement by finding additional evidence, particularly for the classification of subgenera, sections and series of the genus. Further exploration on its origin, evolution, migration and dispersal in the Old World is needed based on phylogenetic construction and biogeographical theory and methods.

Taxonomic research of Chinese Epimedium

Progress in taxonomy of Chinese Epimedium

Since 1975 about 45 Epimedium species endemic to China have been published (Ying, 1975, Ying, 2001, Ying et al., 2011, Zhang et al., 2016b, Wang et al., 2017, Wei et al., 2017). These new species have greatly enriched our understanding of Chinese Epimedium. However, with so many new species published in such a short period of time, it is inevitable that some taxonomic problems of Chinese Epimedium appear. Researchers have conducted a series of taxonomic revisions on Chinese Epimedium based on classical classification and molecular phylogenetic studies (He et al., 2003, Zhang et al., 2011, Zhang et al., 2014a, Zhang et al., 2014b, Zhang et al., 2015a, Zhang et al., 2015b, Xu et al., 2016). Here we review the following five main revisions of Chinese Epimedium.

Taxonomic revision of unifoliolate Chinese Epimedium

Six Chinese Epimedium species, E. simplicifolium T. S. Ying, E. baojingense, E. zhushanense K. F. Wu & S. X. Qian, E. glandulosopilosum H. R. Liang, E. elachyphyllum and E. muhuangense S. Z. He & Y. Y. Wang are the only species of the genus once described with unifoliolate leaves (Stearn, 2002, Wang et al., 2017). Zhang et al. (2011) reviewed the former five species, treated E. simplicifolium as the synonym of E. acuminatum and proposed that E. baojingense, E. zhushanense and E. glandulosopilosum have predominantly trifoliolate and occasionally unifoliolate leaves. Furthermore, because the protologue of E. baojingense lacks the descriptions about flowers and fruits (Chen & Yang, 1982), Zhang et al. (2011) supplemented these descriptions and proposed that the species is usually with racemose and sometimes paniculate with glandular hairs, instead of being racemose with dark-yellow puberulous hairs in its protologue. Similarly, some morphological characters of E. zhushanense, E. glandulosopilosum and E. elachyphyllum, such as inflorescence and flower character, were also revised by Zhang et al. (2011). In addition, neotypes for E. zhushanense and E. glandulosopilosum were designated because the type of the two species had been lost (Zhang et al., 2011).

All Epimedium plants initially have several unifoliolate euphylla after seed germination. The Epimedium species with trifoliolate leaves are occasionally found with cauline unifoliolate leaves. E. elachyphyllum and E. muhuangense are the only two species in Epimedium which have leaves consisting of a single leaflet. Both species occur in two nearing counties of Tongren, Guizhou province, China and have very similar morphological characters. When E. muhuangense was published, Wang et al. (2017) described that the species could be different from E. elachyphyllum by its stout and short rhizomes, two opposite glabrous leaves on flowering stems and paniculate inflorescences. However, according to our field investigation on the type locality, we found that E. elachyphyllum occasionally has two alternate or opposite unifoliolate leaves on the flowering stem and the inflorescence is often paniculate with the lower peduncles bearing 2–5 flowers (Zhang et al., 2011). The two species are only known from the type localities and further explorations on their morphological variations as well as on their taxonomic relationships are needed.

Taxonomic clarification of E. wushanense species complex

Epimedii Folium Wushanensis is embodied as traditional Chinese medicinal material in Chinese Pharmacopoeia (Chinese Pharmacopoeia Commission, 2020), in which E. wushanense is the only botanical origin of the medicinal material. However, the practical application of Epimedii Folium Wushanensis was very chaotic, because its active components were very different among various distribution regions (Pei, Guo, & Huang, 2008). Guo et al. (2007) proposed that E. wushanense was a species with similar leaf shapes and various flower characters. Furthermore, Guo et al. (2007) reported E. pseudowushanense which had been previously used as E. wushanense. However, E. pseudowushanense was treated as an insufficiently known species in Flora of China (Ying, Boufford, & Brach, 2011). Zhang et al. (2014a) studied all seven type specimens of E. wushanense and conducted field investigations covering all the type localities and the regions representing all morphological differentiations of the species. The results showed that E. wushanense, described in Flora Reipublicae Popularis Sinicae (Ying, 2001) and Flora of China (Ying, Boufford, & Brach, 2011), includes four species similar in leaflet shape: E. wushanesne, E. ilicifolium, E. jinchengshanense (sp. nov.) and E. pseudowushanense (Fig. 5). The original description of E. wushanense was based on the seven type specimens representing the first three of the four species, not just on the holotype. The holotype T.P. Wang 10,757 (PE) and the two paratypes, T.P. Wang 10,345 (PE) and G.H. Yang 57,725 (PE), belong to one Epimedium species, which was therefore delimited as E. wushanense. Except for the paratype P.T. Nee 37 (CDBI) identified as E. ilicifolium, the remaining three paratypes, Sichuan Econ. Pl. Exped. Nan 2 (CDBI, KUN, PE, SAU, SM), 2742 (CDBI, KUN, PE, SAU) and 5018 (KUN, PE), represent the new species, E. jinchengshanense. Furthermore, Flora of China (Ying, Boufford, & Brach, 2011) listed Guangxi and Guizhou as distribution localities of E. wushanense. Precisely, the so-called E. wushanense from Guangxi and Guizhou is E. pseudowushanense. In addition, Stearn (2002) classified E. wushanense into ser. Dolichocerae and E. ilicifolium into ser. Davidianae. However, the description of E. wushanense is that of E. jinchengshanense in Stearn’s (2002) monograph. E. wushanense should be placed in ser. Davidianae due to its petals having long spurs with obvious basal lamina. E. ilicifolium has petal spurs without basal lamina and should be relocated into ser. Dolichocerae. E. wushanense, E. jinchengshanense, E. ilicifolium and E. pseudowushanense, can not only be easily differentiated from their corolla characters, but also have small differences in leaflet morphology. Furthermore, each of the four species have relatively independent distribution regions.

Fig. 5

Photos of E. wushanense (A–C), E. ilicifolium (D–F), E. jinchengshanense (G–I) and E. pseudowushanense (J–L). Scale bar = 5 cm in plate A, G, J, and scale bar = 1 cm in plate B, C, D, E, F, H, I, K and L.

Revision of three Epimedium species with controversies on flower characters

Three Chinese Epimedium species, E. reticulatum C. Y. Wu ex S. Y. Bao, E. shuichengense S. Z. He and E. truncatum have been controversial on flower characters (Ying, 2001, Stearn, 2002, Guo et al., 2008, Ying et al., 2011). In the protologue, Bao (1987) described E. reticulatum with small flowers bearing calcariform and 1–2 mm long petals and Stearn (2002) classified it into ser. Brachycerae. However, the species was descried with horn-shaped and ca. 4.5 mm long petals in Flora Reipublicae Popularis Sinicae (Ying, 2001) and Flora of China (Ying, Boufford, & Brach, 2011). Guo et al. (2008) proposed that E. reticulatum had long-spurred petals with a close affinity to E. membranaceum and that it should belong to ser. Dolichocerae. According to a series of studies, Zhang et al. (2015a) found that all the eight sheets of the type specimens actually represent two species, E. reticulatum and E. membranaceum, which might be confused when collected. For the holotype, the main element belongs to E. reticulatum but lacks flowers while the materials conserved in the small paper bag of the specimen contain the flowers of E. membranaceum, the leaves of E. reticulatum and the fruits probably from both the two species. Five sheets of the seven isotypes without flowers belong to E. reticulatum, while the other two sheets with flowers belong to E. membranaceum. As researchers had been learning about the species only from these type specimens, all the previous descriptions of the flowers of E. reticulatum were actually based on those of E. membranaceum. The great flower differences, described by different researchers, may probably be caused by observing flowers of E. membranaceum at different developmental stages. Therefore, Zhang et al. (2015a) re-described the flower of E. reticulatum based on observations of the type locality and moved it to ser. Campanulatae according to the flower features (small and campanulate flowers, flat petal with slightly cucullate base), which was supported by molecular phylogenetic evidence (Zhang et al., 2014b). Furthermore, according to Art. 9.14 of the ICN (McNeill et al., 2012), the lectotype and isolectotypes of E. reticulatum were also designated. In addition, E. shuichengense and E. truncatum were also revised, E. shuichengense was adjusted from ser. Campanulatae into ser. Davidianae and a neotype for E. truncatum was designated (Zhang et al., 2015a).

Synonyms in Chinese Epimedium

Epimedium is an intractable taxon that has many species with great variations in morphology. As these variations are insufficiently understood, some new Epimedium species were published which are, in fact, synonymous with the existing species. Since 1975, six species and two varieties of Chinese Epimedium have been reduced to synonyms. E. simplicifolium and E. chlorandrum Stearn was treated as two synonyms of E. acuminatum, E. rhizomatosum Stearn was placed as a synonym of E. membranceum, E. brachyrrhizum Stearn as a synonym of E. leptorrhizum, E. dewuense S. Z. He, Probst & W.F. Xu as a synonym of E. dolichostemon, E. lobophyllum L. H. Liu & B. G. Li and E. sagittatum var. pyramidale (Franch.) Stearn as synonyms of E. myrianthum, and E. sagittatum var. oblongifoliolatum Z. Cheng as a synonym of E. borealiguizhouense (Ying et al., 2011, Zhang et al., 2011, Zhang et al., 2015b, He, 2014).

Ying (1975) treated E. membranceum as a synonym of E. davidii, which had been accepted by Flora Reipublicae Popolaris Sinica (Ying, 2001) and Flora of China (Ying, Boufford, & Brach, 2011). However, E. membranceum and E. davidii are two different species. E. membranceum has leaves with three leaflets and petals without basal lamina, belonging to ser. Dolichocerae, while E. davidii has leaves with five or three leaflets and petals with obvious basal lamina, belonging to ser. Davidianae (Fig. 6A–F).

Fig. 6

Photos of E. davidii (A–C), E. membranceum (D–F), E. epsteinii (G–I) and E. shennongjiaense (J–L). Scale bar = 2 cm in plate A, D, G, J, and Scale bar = 5 mm in plate B, C, E, F, H, I, K and L.

In addition, the above results of classical taxonomic research have been well supported by molecular phylogenetic studies except that E. lobophyllum and E. sagittatum var. pyramidale were not involved (Zhang et al., 2014b). For example, E. simplicifolium and E. chlorandrum were treated as two synonyms of E. acuminatum, and the phylogenetic tree based on AFLP data showed the three species mixedly clustered into a separate clade. Classical taxonomic studies supported E. membranceum and E. davidii as two distinct species and molecular phylogenetic studies demonstrated that E. davidii grouped into a cluster consisting of the species from ser. Campanlatae and ser. Davidianae, while E. membranceum clustered into a clade with E. acuminatum of ser. Dolichoceae (Zhang et al., 2014b).

Clarification of the distribution area of E. epsteinii

E. epsteinii Stearn is a species endemic to Tianping Mountain of Hunan province (Stearn, 1997). Except for the protologue, we had no other information about it and the species was treated as an insufficiently known species in Flora of China (Ying, Boufford, & Brach, 2011). Xu et al. (2016) reported two new distribution localities, Ruyuan county of Guangdong and Jianshi county of Hubei. We observed the living individuals of E. epsteinii cloned from its holotype specimen, Darrell Probst CPC 94.0255 (K) at the garden of Mr. Darrell Probst in Hubbardston, Mass., U.S.A in 2001, investigated the species at the type localities several times from 2006 to 2020 and recognised that E. epsteinii is a valid species (Fig. 6G–I). Furthermore, we collected E. leptorrhizum at Ruyuan county of Guangdong Province which was recognised as E. epsteinii by Xu et al. (2016) at 2005 and 2016. As a result, we found that the species distributed in Ruyuan county of Guangdong Province should not be E. epsteinii, but is E. leptorrhizum. Although both E. epsteinii and E. leptorrhizum have elongated rhizomes, the two species differ obviously in the leaflet and flower morphology. E. epsteinii has leaflets with an acuminate apex and sparse minute appressed bristle-like hairs. E. leptorrhizum has leaflets with a long acuminate apex, many impressed veins on the adaxial surface and bears reddish pubescence on the mid-vein and lateral veins of the abaxial surface, especially dense at the insertion of petiolules. E. epsteinii has petals with 5 mm tall lamina which enclose stamens and belongs to ser. Davidianae, while E. leptorrhizum has petals without basal lamina and belongs to ser. Dolichocerae. E. shennongjiaense Y.J. Zhang & J.Q. Li is a species from Hubei (Zhang & Li, 2009) (Fig. 6J–L), which is mostly similar to E. epsteinii, but can be distinguished by its compact rhizomes, acuminate inner sepals and its petals which are slightly shorter than or nearly as long as the inner sepals with straight spurs.

Taxonomic problems on Chinese Epimedium

Though researchers have conducted a series of taxonomic studies on Chinese Epimedium, the genus is a very intractable taxon and there are controversies in some Chinese species. We here conclude that the taxonomic problems of Chinese Epimedium need further research in the following six domains.

Epimedium sagittatum species complex

E. sagittatum complex is referred to as E. sagittatum and several of its related species. E. sagittatum is distributed in Anhui, Chongqing, Fujian, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangxi, Zhejiang, while several of its related species are mainly distributed in West Hunan and Hubei, Chongqing and Guizhou (Zhang et al., 2014b). The complex is the most controversial in the taxonomy of the genus. This complex has great morphological variations within and among different species and shows unclear morphological boundaries among species (He et al., 2003, Xu et al., 2013, Zhang et al., 2014b). Furthermore, in the complex, only E. sagittatum is one of the four original plants of Epimedii Folium in Chinese pharmacopoeia (Chinese Pharmacopoeia Commission, 2020). However, E. sagittatum has great variations in bioactive components resulting in many populations not meeting the quality standards of Epimedii Herba in Chinese Pharmacopoeia (Chinese Pharmacopoeia Commission, 2020), while many populations of its related species have high contents of bioactive components (Guo et al., 1996, Guo et al., 2008, Pei et al., 2007, Shen et al., 2007, Chen et al., 2015). For the further development and utilisation of Chinese Epimedium resources, it is very necessary to clarify the taxonomic problems which exist in the complex.

Both Stearn, 2002, He et al., 2003 treated E. sagittatum var. pyramidale as the synonym of E. myrianthum, which was accepted by Flora of China (Ying, Boufford, & Brach, 2011). He et al. (2003) also treated E. sagittatum var. glabratum T. S. Ying and E. coactum H. R. Liang & W. M. Yan var. lobophyllm H. R. Liang as synonyms of E. myrianthum, and published E. sagittatum var. guizhouense S. Z. He et W. M. Yan and E. myrianthum var. jianheense S. Z. He et W. M. Yan. However, Flora of China (Ying, Boufford, & Brach, 2011) sustained E. sagittatum var. glabratum, adjusted E. coactum as the synonym of E. pubescens, and did not accept E. sagittatum var. guizhouense and E. myrianthum var. jianheense. According to our previous morphological studies on the species complex, E. coactum and E. pubescens are obviously different species and it is inappropriate to adjust E. coactum as the synonym of E. pubescens. For E. myrianthum var. jianheense, it was not mentioned in the papers by Shunzhi He (He et al., 2005, Wang et al., 2009) and his illustrated handbook of Chinese Epimedium (He, 2014). Zhang et al. (2015b) adjusted E. sagittatum var. oblongifoliolatum as a synonym of E. borealiguizhouense. The E. sagittatum complex is here reviewed which consists of seven species and three varieties, E. sagittatum, E. myrianthum, E. multifolium T. S. Ying, E. borealiguizhouense, E. pudingense S. Z. He, Y. Y. Wang & B. L. Guo, E. jingzhouense G. H. Xia & G. Y. Li, E. coactum, E. sagittatum var. glabratum, E. sagittatum var. guizhouense and E. coactum var. longtohum.

We have analysed the intra-species variations of E. sagittatum on morphological, genetic and chemotypic diversity, based on a common garden experiment. The results showed that chemotype variation has a significant genetic basis and the relationships of different populations, based on morphological and genetic diversity, were related with their geographical distribution (Liang et al., 2013, Chen et al., 2015). Based on AFLP data, phylogenetic analyses were also conducted on five species and three varieties of the E. sagittatum species complex collected from 25 localities (Zhang et al., 2014b). The phylogenetic tree demonstrated that the 25 populations of the species complex were subdivided in a manner closely correlated with the geographical distribution. E. multifulum, E. coactum and E. coactum var. longtoutum were embedded in different populations of E. sagittatum, while E. sagittatum var. glabratum is more closely related with E. myrianthum and E. borealiguizhouense, and not with the original variant of E. sagittatum. It is urgent to achieve a scientific taxonomic treatment of E. sagittatum species complex.

Epimedium pubescens species complex

E. pubescens is one of the four original plants of Epimedii Folium in Chinese pharmacopoeia (Chinese Pharmacopoeia Commission, 2020). In morphology, E. pubescens is very similar to E. stellulatum Stearn which was not included in Chinese pharmacopoeia. The two species flower earlier in Chinese Epimedium and their white small flowers appear beautiful and chic in early spring. E. pubescens has a relatively wide distribution mainly in the Sichuan Basin and its surrounding mountains, northwestern Chongqing, southern Shaanxi and southernmost Gansu (Zhang, 2009, Liu et al., 2017b). E. stellulatum is only recorded in Fangxian, Shiyan, Yunxi and Zhushan of Hubei province (Zhang, 2009). Liu et al. (2017b) analysed the genetic diversity and indumentum type on the abaxial surface of leaflets from 14 populations of E. pubescens and one population of E. stellulatum. Based on the ISSR marker, the UPGMA tree showed that the two species did not form two monophyletic clusters with the only one population of E. stellulatum being embedded in the 14 populations of E. pubescens. Furthermore, the indumentum type of E. stellulatum was the same as that of E. pubescens from Nanzheng of Shaanxi province. As a result, Liu et al. (2017b) proposed that E. stellulatum should not be an independent species, but a synonym or a variety of E. pubescens. Zhi et al. (2018) studied the indumentum type on the abaxial surface of leaflet of E. pubescens and E. stellulatum based on a more comprehensive sample collection, and also proposed that E. stellulatum should be an infra-specific taxon of E. pubescens. Along with further studies on the E. pubescens species complex, a more scientific relationship of the two species and a more natural taxonomic treatment on the species complex can be achieved.

Epimedium franchetii species complex

The E. franchetii species complex was proposed by Gao (2011), who considered that the complex should consist of E. franchetii, E. baojingense, E. zhushanense and E. lishichenii. Liu et al. (2016) conducted morphological analyses on the nine populations of the species complex in the field and observed some morphological transitional populations between E. franchetii, E. lishichenii and E. baojingense. Therefore, Liu et al. (2016) proposed that E. zhushanense was an independent species and should be removed from the E. franchetii complex, E. baojingense should be treated as E. franchetii var. baojingense (ecological race) while E. lishihchenii should be treated as E. franchetii ssp. lishihchenii (geographical race). However, E. franchetii was published in 1996, E. lishichenii in 1997 and E. baojingense in 1982 (Chen and Yang, 1982, Stearn, 1996, Stearn, 1997). Because E. baojingense was published earlier than the other two species, it was invalid to treat E. baojingense and E. lishichenii as the infra-species taxa of E. franchetii according to Art. 11.4 of the ICN (Turland et al., 2018). Among the species complex, E. zhushanense is relatively easily distinguishable from the above three species on the basis of flower characters: E. zhushanense has purple flowers and a relatively higher length ratio of the internal sepals to the petals, while the other three species usually have yellow flowers except that E. franchetii was reported with a pale pink flower population (Gao, 2011). However, Gao (2011) also found that one population of E. zhushanense has the same indumentum as E. baojingense. For achieving a more natural taxonomic treatment of the species complex, specimens deposited in main herbaria should be systematically analysed and more comprehensive field investigations are needed in future research.

Epimedium platypetalum and E. campanulatum

Series Campanulatae bears campanulate and small flowers with petals being flat or having a slight nectarial swelling at the base. Stearn (2002) proposed that ser. Campanulatae might be the most primitive in the flower evolution of Epimedium. The series comprises of four species, E. platypetalum, E. campanulatum Ogisu, E. ecalacaratum G. Y. Zhong and E. reticulatum (Stearn, 2002, Zhang et al., 2015a). All the four Epimedium species are mainly distributed in Sichuan province but one new distribution of E. platypetalum was reported in Shanxi province (Lu et al., 1989). Among the four species, E. reticulatum and E. ecalcaratum have petals with a slightly cucullate base, while the whole petals of E. platypetalum and E. campanulatum are flat. Furthermore, E. reticulatum and E. ecalcaratum are relatively distinctive species, and E. reticulatum can be easily distinguished from E. ecalcaratum by its thick leathery leaflets with conspicuous reticulate veins on both surfaces and much smaller flowers.

E. platypetalum and E. campanulatum are most closely related to each other and have some taxonomic controversies. Moreover, E. campanulatum has been listed as an insufficiently known species in Flora of China (Ying, Boufford, & Brach, 2011). Liu et al. (2017a) detailedly compared the living individuals of E. platypetalum from Nanzhen of Shaanxi province and those of E. campanulatum from Dujiangyan of Sichuan province, China. The two populations can be differentiated in terms of rhizomes, the leaf number of flower stems and petals. However, the key problem is that we cannot well understand the two species. Firstly, for E. platypetalum, except for the type specimen (Limpricht 1386 (WRSLE, WU)) and one collection from 1993 (Ogisu 93,085 (K)) (Ogisu, 1995, Stearn, 2002), no other collection was attained from the type locality, Wenchuan county of Sichuan province. Liu et al., (2017a) cited a specimen (S.Y. Chen 5210 (NAS)) as E. platypetalum which was collected from Maoxian, another county near the type locality of Wenchuan. However, we observed the other sheets of the specimen deposited in SZ and SM, and recognised that the specimen should belong to E. pauciflorum which has long spur petals with an obvious basal lamina. Except for the type locality, we knew the species only from its other two distribution localities far away from the type locality, Nanjiang of northeastern Sichuan and Nanzheng of south-western Shaanxi (Lu et al., 1989, Liu et al., 2016). Therefore, the morphological characters of E. platypetalum are not sufficiently researched as well as our understanding of the species at the type locality. Secondly, we knew E. campanulatum only from the type locality, Dujiangyan, Sichuan, near the type locality of E. platypetalum. Stearn (2002) proposed that E. campanulatum differed from E. platypetalum in having narrowly ovate leaflets, while those of E. platypetalum are broadly ovate or almost orbicular.

In general, it is difficult to compare E. platypetalum and E. campanulatum because of a lack of sufficient investigations and collections. For attaining a scientific taxonomy treatment of the two species, the following problems need to be addressed: 1) What are the standard morphological characters of E. platypetalum at the type localities? 2) The two distribution localities of E. platypetalum, Nanjiang and Nanzheng, are much farther from its type locality, while the two type localities of E. platypetalum and E. campanulatum are very near. What is the difference between the two populations of E. platypetalum and standard E. platypetalum and E. campanulatum at their type localities? 3) What are the actual distribution areas and morphological variations of E. platypetalum and E. campanulatum? What are the differences between E. platypetalum and E. campanulatum?

Epimedium koreanum and E. grandiflorum

E. koreanum is one original species of Epimedii Folium in Chinese pharmacopoeia (Chinese Pharmacopoeia Commission, 2020). E. koreanum is very similar to E. grandiflorum C. Morren and there are controversies on the taxonomic treatment of the two species (Stearn, 2002). In Flora of China, E. koreanum was recorded in Anhui, Jilin, Liaoning and Zhejiang of China, Japan and North Korea (Ying, Boufford, & Brach, 2011). According to the specimen examination and field investigation, we found that E. koreanum is only distributed in Jilin and Liaoning of China and has no distribution in Anhui and Zhejiang of China. Furthermore, it is reported that E. koreanum has been also distributed in South Korea (Flora of Korea Editorial Committee, 2008, Lee et al., 2015).

In Stearn’s (2002) monograph about Epimedium, E. koreanum was described with distribution in Korea, while E. grandiflorum was described with distribution in Japan, North Korea and Northeast China which was recognised as E. koreanum in Flora of China (Ying, Boufford, & Brach, 2011). E. koreanum was recognised with elongated rhizome and yellow flowers, while E. grandiflorum was recognised with compact rhizome and white, pale yellow, deep rose, red–purple or violet flowers (Stearn, 2002). However, through specimen examination we found that E. grandiflorum in North Korea and Northeast China possesses elongated rhizomes. Furthermore, E. grandiflorum are usually with white, pale yellow or yellow flowers in the above two regions. Except that E. grandiflorum bears deep rose, red–purple or violet flowers in Japan, it is difficult to find a stable distinguishing feature between E. koreanum and E. grandiflorum.

Flora of China (Ying, Boufford, & Brach, 2011) and Flora of Korea (Flora of Korea Editorial Committee, 2008) only described E. koreanum, in both of which the distribution of E. koreanum covered that of E. grandiflorum. However, E. koreanum was treated as a variant of E. grandiflorum, var. koreanum (Nakai) K. Suzuki in Flora of Japan (Suzuki, 1995). Furthermore, Stearn (2002) proposed that E. grandiflorum included three formaes, forma grandiflorum, forma flavescens Stearn and forma violaceum (C.Morren) Stearn. Flora of Japan (Suzuki et al., 1995) described that E. grandiflorum was composed of three varieties, var. grandiflorum, var. koreanum and var. thunbergianum (Miq.) Nakai. The definition and taxonomy of E. koreanum and E. grandiflorum and the infra-species taxa of E. grandiflorum are often confused. In order to achieve a more natural taxonomic revision on E. grandiflorum and E. koreanum, it is necessary to have comprehensive specimen examinations and field investigations of the two species in all distribution regions.

Other taxonomic problems in Chinese Epimedium

China has the most abundant species of Epimedium among which about 45 species and three varieties had been published since 1975. Although Epimedium species are usually endemic with relatively narrow distribution, the recognition of some Chinese species of the genus is obviously insufficient. Therefore, further investigation on their distribution range and morphological variation is needed. For instance, some newly published species are only known from their type locality. Some sister species, such as E. qingchengshan and E. fargesii, E. elachyphyllum and E. muhuangense S. Z. He & Y. Y. Wang, need further investigation to clarify their relationships. On the other hand, Epimedium species are distributed in remote mountainous areas, so it is very hard to investigate these lovely plants. There are still some regions in China where investigations of Epimedium are insufficient to some extent, such as eastern China and western Sichuan. In order to better explore and utilize Epimedium plants, these taxonomic problems of Chinese Epimedium should be resolved.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.