Chromosome studies in the aquatic monocots of Myanmar: A brief review with additional records.

Myanmar (Burma) constitutes a significant component of the Indo-Myanmar biodiversity hotspot, with elements of the Indian, the Indochina, and the Sino-Japanese floristic regions, yet thus far only a few reliable sources of the country's flora have been available. As a part of a contribution for the floristic inventory of Myanmar, since it is important in a floristic survey to obtain as much information as possible, in addition to previous two reports, here we present three more chromosome counts in the aquatic monocots of Myanmar: Limnocharisflava with 2n = 20, Sagittariatrifolia with 2n = 22 (Alismataceae), and Potamogetondistinctus × Potamogetonnodosus with 2n = 52 (Potamogetonaceae); the third one is new to science. A brief review of cytological researches in the floristic regions' 45 non-hybrid aquatic monocots plus well investigated two inter-specific hybrids that are recorded in Myanmar is given, indicating that the further works with a focus on species in Myanmar that has infra-specific chromosome variation in the floristic regions will address the precise evolutionary history of the aquatic flora of Myanmar.

Introduction

With its wealth of plant diversity, Myanmar (Burma) constitutes a significant component of the Indo-Myanmar biodiversity hotspot with elements of the India, the Indochina, and the Sino-Japanese floristic regions (ca, 13,500 vascular plants: Van Dijk et al. 2004; Tanaka 2010). Yet, while neighboring countries’ floristic diversity has been exposed through international projects, such as Flora of China, Flore du Cambodge, du Laos et du Vietnam, and Flora of Thailand, thus far no reliable sources of Myanmar’s flora have been published except a checklist of spermatophytes contributed by Kress et al. (2003). In order to revise the flora of Myanmar, a decade-long continuous inventory has been conducted by Japanese botanists (Tanaka 2005), which thus far partly contributed a local checklist (Mt. Popa: Tanaka et al. 2006) and a taxon-specific checklist (aquatic plants: Ito and Barfod 2014).

The aim of floristic research is not only to count the total number of species but also to evaluate the native flora’s evolutionary origins by comparing with related floristic regions. From this aspect, it is useful to obtain as much information as possible, e.g., chromosome data (Sanders et al. 1983). This is especially important for floristic surveys for aquatic plants, in which infra- or inter-specific chromosome variation is widely known (Les and Philbrick 1993). The proportion of species for which the chromosome number is known is less than 1% in some little-collected tropical areas (Stace 2000), probably including the southeast Asian country of Myanmar.

Aquatic plants, which is polyphyletically evolved in fern and fern allies, basal angiosperms, monocots, and eudicots, is known as having numerous chromosomal variation, thus an excellent model for this aim. Here, in addition to the previous contributions of chromosome counts for new or noteworthy aquatic plants from Myanmar (: Ito et al. 2014b; : Ito et al. 2009), we present three more chromosome counts for the aquatic monocots of Myanmar: (), (), and × (). A brief review of cytological researches in 45 non-hybrid aquatic monocots plus two well-investigated inter-specific hybrids in Myanmar is also given with a broad focus on those distributed in neighboring areas, i.e., the Indian, the Indochina, and the Sino-Japanese floristic regions.

Materials and methods

Chromosome observation

Plant materials of (), (), (), (), and × () were collected in the expeditions to Myanmar (Bago Division and Shan State) in 2008. The collections were rigorously identified based on morphological characters using the original protologues as well as a previous taxonomic treatment by Cook (1996). × () was identified by DNA barcoding method (Ito et al. 2014a). The first set of the voucher specimens was retained in Forest Department Office, Ministry of Environmental Conservation and Forestry, Union of Myanmar (RAF); the duplicates are deposited in two Japanese herbaria: Makino Botanical Garden (MBK) and the University of Tokyo (TI).

Root tips collected in the field were pretreated with 0.002 M 8-hydroxyquinoline at 4 °C in 12 h, and fixed with freshly mixed Carnoy’s fixative (3: 1 ethyl alcohol: acetic acid) for at least 30 min, and then preserved at 4 °C in 12 h. For microscopic observation, root tips were soaked in 1 N HCl for 1 h followed by 10 min at 60 °C. After being immersed in tap water, the materials were stained in a drop of 1.5% orcein acetate solution on a slide glass in 5 min., and then squashed. Then somatic chromosome numbers of the three taxa were obtained by light microscopic examination. For each species, at least two cells were used to confirm the numbers.

Distribution for each species follows Ito and Barfod (2014).

Literature review

Chromosome researches for aquatic monocots of Myanmar were reviewed with a broad focus on Myanmar and related floristic regions, i.e., the Indian, the Indochina, and the Sino-Japanes floristic regions. The focal species include 45 non-hybrid aquatic monocots listed in Ito and Barfod (2014), Ito et al. (2014a) as well as well-investigated two inter-specific hybrids (Ito et al. 2014a). Initial literature search was carried out with Fedorov (1969) as well as Index to Plant Chromosome Numbers (Missouri Botanical Garden, http://mobot.mobot.org/W3T/Search/ipcn.html), followed by extensive literature review with original references. For some species, mostly cosmopolitan ones, only a few representative literature references are given for each chromosome number. Since a comprehensive cytological review was given for aquatic plants (Les and Philbrick 1993), including almost all the taxa listed in the present study, our literature review focused on literature published in 1993 or later. Due to incapability of original references, some rare chromosome counts are not included; those references are mostly published in 1970 or earlier, and written not in English. No detailed references are given for and because an exhaustive cytological review was published by Kaplan et al. (2013), Talavera et al. (1993).

Checklists

Chromosome counts for the aquatic monocots of Myanmar

Bonpl., 1808

(L.) Buchenau, 1868

Type status: Other material. Occurrence: recordedBy: Y. Ito; Location: country: Myanmar; stateProvince: Bago; municipality: Pyat Township; locality: along the roadside, paddy field, ca. 30 km east of Pyat; verbatimLatitude: 18°49'44"N; verbatimLongitude: 95°18'06"E; Event: eventDate: 7 Dec 2008; Record Level: collectionID: N. Tanaka & al. 080776; institutionCode: MBK, RAF, TI

Distribution

Native to Americas; naturalized to tropical Asia.

Notes

Chromosome counts: 2n = 20 (Fig. 1; obtained in this study).

Figure 1.

Somatic chromosome of . Bar indicates 5 μm.

L., 1753

L., 1753

Type status: Other material. Occurrence: recordedBy: Y. Ito; Location: country: Myanmar; stateProvince: Shan; verbatimLocality: Pindaya; verbatimLatitude: 20°59'57"N; verbatimLongitude: 96°39'59"E; Event: eventDate: 1 Dec 2008; Record Level: collectionID: N. Tanaka & al. 080623

Bangladesh, Bhutan, China (nationwide), India (nationwide), Indonesia (Borneo, Java, Sulawesi), Japan, Malaysia (Peninsular), Myanmar, Nepal, Pakistan, Philippines, Thailand; Oceania.

Chromosome counts: 2n = 22 (Fig. 2; obtained in this study).

Figure 2.

Somatic chromosome of . Bar indicates 5 μm.

L., 1753

Magnus, 1870

Type status: Other material. Occurrence: recordedBy: Y. Ito; Location: country: Myanmar; stateProvince: Shan; verbatimLocality: Inlay Lake, Nyaung Shwe Township; verbatimLatitude: 20°32'02"N; verbatimLongitude: 96°53'53"E; Event: eventDate: 3 Dec 2008; Record Level: collectionID: N. Tanaka & al. 080642; institutionCode: MBK, RAF, TI

India (Central, Southern), Myanmar, Sri Lanka.

Chromosome counts: 2n = 24 (Fig. 3; After Ito et al. 2014b; reproduced with publisher's permission).

Figure 3.

Somatic chromosome of . Bar indicates 5 μm.

Planch., 1849

(Roxb.) Thwaites, 1864

Type status: Other material. Occurrence: recordedBy: Y. Ito; Location: country: Myanmar; stateProvince: Shan; verbatimLocality: Near Yae Aye Kan Dam, Yae Aye Kan, Kalaw Township; verbatimLatitude: 20°35'37"N; verbatimLongitude: 96°31'46"E; Event: eventDate: 26 Nov 2008; Record Level: collectionID: N. Tanaka & al. 080058; institutionCode: MBK, RAF, TI

Bangladesh, China (Southern), India (Eastern, Northern, Southern), Myanmar, Nepal, Sri Lanka, Thailand, Vietnam; Yemen, and Sudan.

Chromosome counts: 2n = 16 (Fig. 4; After Ito et al. 2009; reproduced with publisher's permission).

Figure 4.

Somatic chromosome of . Bar indicates 5 μm.

L., 1753

Type status: Other material. Occurrence: recordedBy: Y. Ito; Location: country: Myanmar; stateProvince: Shan; verbatimLocality: Inle Lake; verbatimLatitude: 20°27'28"N; verbatimLongitude: 96°50'37"E; Event: eventDate: 4 Dec 2008; Record Level: collectionID: N. Tanaka & al. 080662; institutionCode: MBK, RAF, TI

Chromosome counts: 2n = 52 (Fig. 5; obtained in this study). The chromosome count for this taxon is new to science.

Figure 5.

Somatic chromosome of × . Bar indicates 2.5 μm.

Analysis

The chromosome counts given for 45 non-hybrid species of aquatic monocots of Myanmar as well as well-investigated two hybrids among them were reviewed with a focus on infra-specific chromosome variation (Table 1). The cited literature references also include chromosome counts obtained from related floristic regions, i.e., the Indian, the Indochina, and the Sino-Japanese floristic regions. For widespread species, cytological information from other regions is cited.

Table 1.

The chromosome counts given for 45 non-hybrid species of aquatic monocots of Myanmar as well as well-investigated two hybrids among them. Those recorded from neighboring regions are also provided. The species that have no chromosome counts anywhere in the world are shown with n/a. For some species, mostly cosmopolitan ones, only a few representative literature references are given for each chromosome number. Note that due to incapability of original references, some rare chromosome counts are not included in this table: 2n = 18, 42, 48 for ; 2n = 18, 22 for (), 2n = 28 for Engl.; 2n = 28 for (Michx.) Engl.; 2n = 20, 50, 60, 80 for ; 2n = 44 for ; 2n = 30, 50 for (); n = 14 (2n = 28), 2n = 10, 12 for ; 2n = 22 for ; 2n = 26, 39 for ; 2n = 22 for (Turr.) Mak.; 2n = 22 for Sims; 2n = 22 for (Sieb.) Ohwi (); 2n = 24 for ; 2n = 60 for ; 2n = 12+1B for (Gorski) A. Braun; 2n = 22, 52, 72, 88, 132 for ; 2n = 16, 22, 28, 33 for (); 2n = 64 for ; 2n = 26, n = 40 (2n = 80) for (); 2n = 60 for (). Also refer to previous cytological reviews (aquatic plants: Les and Philbrick 1993; : Kaplan et al. 2013; : Talavera et al. 1993).

Order	Family	Species	Chromo-some number	Floristic region
				Indian	Myanmar	Indo-china	Sino-Japanese	Others
Acorales	Acoraceae	Acorus calamus L.	2n = 24	Subramanian and Munian (1988)				Chepinoga et al. (2008)
Acorales	Acoraceae	Acorus calamus L.	2n = 35					Krahulcová (2003)
Acorales	Acoraceae	Acorus calamus L.	2n = 36					Packer and Ringius (1984)
Acorales	Acoraceae	Acorus calamus L.	2n = 44				Wang et al. (2001)
Acorales	Acoraceae	Acorus calamus L.	2n = 45	Ramachandran (1978)
Acorales	Acoraceae	Acorus calamus L.	2n = 66				Wang et al. (2001)
Acorales	Acoraceae	Acorus gramineus Sol. ex Aiton	2n = 24				Wang et al. (2001)
Acorales	Araceae	Cryptocoryne crispatula Engl.	2n = 36	Arends et al. (1982)
Acorales	Araceae	Cryptocoryne crispatula Engl.	2n = 54	Jacobsen (1977)
Acorales	Araceae	Cryptocoryne cruddasiana Prain	n/a
Acorales	Araceae	Pistia stratiotes L.	2n = 28	Ramachandran (1978), Subramanian and Munian (1988)
Acorales	Araceae	Landoltia punctata (G. Mey.) Les & D.J. Crawford	n/a
Acorales	Araceae	Lemna aequinoctialis Welw.	2n = 40	Urbanska-Worytkiewicz (1975) (Lemna perpusilla Torr.)			Beppu et al. (1985)
Acorales	Araceae	Lemna trisulca L.	2n = 20					Urbanska-Worytkiewicz (1975)
Acorales	Araceae	Lemna trisulca L.	2n = 40					Urbanska-Worytkiewicz (1975)
Acorales	Araceae	Lemna trisulca L.	2n = 60					Urbanska-Worytkiewicz (1975); Löve and Löve (1981)
Acorales	Araceae	Lemna trisulca L.	2n = 80					Urbanska-Worytkiewicz (1975)
Acorales	Araceae	Spirodela polyrrhiza (L.) Schleid.	2n = 40					Löve and Löve (1981), Al-Bermani et al. (1993)
Acorales	Araceae	Spirodela polyrrhiza (L.) Schleid.	2n = 42					Chepinoga et al. (2008)
Acorales	Araceae	Spirodela polyrrhiza (L.) Schleid.	2n = 80					Geber and Schweizer (1988)
Acorales	Araceae	Wolffia globosa (Roxb.) Hartog &Plas	n/a
Alismatales	Alismataceae	Alisma plantago-aquatica L.	2n = 14	Mehra and Pandita (1984)			Wang et al. (1987); Uchiyama (1989) (var. Alismaplantago-aquaticaorientale Samuel)
Alismatales	Alismataceae	Caldesia parnassifolia (Bassi ex L.) Parl.	n/a
Alismatales	Alismataceae	Limnocharis flava (L.) Buchenau	2n = 20		This study		Uchiyama (1989)	Davidse (1981), Forni-Martins and Calligaris (2002)
Alismatales	Alismataceae	Sagittaria trifolia L.	2n = 22		This study		Uchiyama (1989); (var. Sagittariatrifoliaedulis (Sieb.) Ohwi)
Alismatales	Hydrocharita	Blyxa aubertii Rich.	2n = 40				Uchiyama (1989)
Alismatales	Hydrocharita	Blyxa echinosperma (C.B. Clarke) Hook. f.	2n = 42				Wang (1986)
Alismatales	Hydrocharita	Blyxa echinosperma (C.B. Clarke) Hook. f.	2n = 74				Uchiyama (1989)
Alismatales	Hydrocharita	Blyxa japonica (Miq.) Maxim. ex Asch. & Gürke	2n = 42				Harada (1956)
Alismatales	Hydrocharita	Blyxa japonica (Miq.) Maxim. ex Asch. & Gürke	2n = 72				Uchiyama (1989)
Alismatales	Hydrocharita	Egeria densa (Planch.) Casp.	2n = 46				Uchiyama (1989), Nakata and Nagai (1998)
Alismatales	Hydrocharita	Egeria densa (Planch.) Casp.	2n = 48					Löve and Löve (1961)
Alismatales	Hydrocharita	Elodea nuttallii (Planch.) H. St. John	2n = 48					Simpson (1986)
Alismatales	Hydrocharita	Hydrilla verticillata (L. f.) Royle	2n = 16	Chaudhuri and Sharma (1978), Pandita and Mehra (1984)			Wang (1986), Uchiyama (1989), Langeland et al. (1992)	Langeland et al. (1992)
Alismatales	Hydrocharita	Hydrilla verticillata (L. f.) Royle	2n = 24	Chaudhuri and Sharma (1978)			Langeland et al. (1992), Nakata and Nagai (1998)	Langeland et al. (1992)
Alismatales	Hydrocharita	Hydrilla verticillata (L. f.) Royle	2n = 32				Langeland et al. (1992)	Langeland et al. (1992)
Alismatales	Hydrocharita	Hydrocharis dubia (Blume) Backer	2n = 16	Pandita and Mehra (1984)			Uchiyama (1989)
Alismatales	Hydrocharita	Najas graminea Delile	2n = 12				You et al. (1991)
Alismatales	Hydrocharita	Najas graminea Delile	2n = 24				Wang (1985), Uchiyama (1989)
Alismatales	Hydrocharita	Najas graminea Delile	2n = 36				Uchiyama (1989)
Alismatales	Hydrocharita	Najas indica (Willd.) Cham.	n/a
Alismatales	Hydrocharita	Najas marina L.	2n = 12				Wang (1985), Uchiyama (1989)
Alismatales	Hydrocharita	Najas marina L.	2n = 24					Viinikka et al. (2008)
Alismatales	Hydrocharita	Najas tenuis Magnus	2n = 24		Ito et al. (2014b)
Alismatales	Hydrocharita	Nechamandra alternifolia (Roxb.) Thwaites	2n = 16	Sharma and Chatterjee (1967)	Ito et al. (2009)
Alismatales	Hydrocharita	Ottelia alismoides (L.) Pers.	2n = 44				Harada (1956), Uchiyama (1989)
Alismatales	Hydrocharita	Ottelia alismoides (L.) Pers.	2n = 66	Chaudhuri and Sharma (1978)
Alismatales	Hydrocharita	Ottelia alismoides (L.) Pers.	2n = 68	Chaudhuri and Sharma (1978)
Alismatales	Hydrocharita	Ottelia cordata (Wall.) Dandy	n/a
Alismatales	Hydrocharita	Vallisneria spiralis L.	2n = 20				Wang (1986)
Alismatales	Hydrocharita	Vallisneria spiralis L.	2n = 24	Chaudhuri and Sharma (1978)
Alismatales	Hydrocharita	Vallisneria spiralis L.	2n = 30	Chaudhuri and Sharma (1978)
Alismatales	Hydrocharita	Vallisneria spiralis L.	2n = 40	Chaudhuri and Sharma (1978), Sarkar et al. (1980)
Alismatales	Aponogetona	Aponogeton lakhonensis A. Camus	n/a
Alismatales	Potamogetona	Potamogeton crispus L.	2n = 52				Kaplan et al. (2013)	Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton crispus L.	2n = 56				Nakata and Nagai (1998)
Alismatales	Potamogetona	Potamogeton distinctus A. Benn.	2n = 52				Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton distinctus A. Benn. × Potamogeton nodosus Poir.	2n = 52		This study
Alismatales	Potamogetona	Potamogeton maackianus A Benn.	2n = 52				Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton maackianus A Benn.	2n = 56			Kaplan et al. (2013)	Uchiyama (1989), Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton × malainoides Miki	2n = 52				Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton lucens L.	2n = 52				Kaplan et al. (2013)	Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton nodosus Poir.	2n = 52					Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton octandrus Poir.	2n = 28				Uchiyama (1989), Nakata and Nagai (1998), Kaplan et al. (2013)
Alismatales	Potamogetona	Potamogeton wrightii Morong	2n = 52				Kaplan et al. (2013)
Alismatales	Potamogetona	Stuckenia pectinata (L.) Börner	2n = 78	Kaplan et al. (2013)				Kaplan et al. (2013)
Alismatales	Potamogetona	Stuckenia pectinata (L.) Börner	2n = 84				Uchiyama (1989)
Alismatales	Ruppiaceae	Ruppia maritima L.	2n = 20	Ito et al. (2010)		Ito et al. (2010)	Ito et al. (2010)	Van Vierssen et al. (1981)
		Ruppia maritima L.	2n = 40				Harada (1956), Ito et al. (2010)	Ito et al. (2010)
Asparagales	Amaryllidaceae	Crinum thaianum J. Schul.	n/a
Commelinales	Pontederiaceae	Eichhornia crassipes (Mart.) Solms	2n = 32					Pedrosa et al. (1999)
Commelinales	Pontederiaceae	Monochoria hastata (L.) Solms	2n = 28	Patwary et al. (1989)
Commelinales	Pontederiaceae	Monochoria hastata (L.) Solms	2n = 80	Patwary et al. (1989)
Commelinales	Pontederiaceae	Monochoria vaginalis (Burm.f.) C. Presl ex Kunth	2n = 24	Christopher (1983) (var. Monochoriavaginalisplantaginea (Roxb.) Solms);Patwary et al. (1989)
Commelinales	Pontederiaceae	Monochoria vaginalis (Burm.f.) C. Presl ex Kunth	2n = 48			Wang and Kusanagi (1996) (var. Monochoriavaginalisangustifolia G.X.Wang)
Commelinales	Pontederiaceae	Monochoria vaginalis (Burm.f.) C. Presl ex Kunth	2n = 52	Christopher (1983), Patwary et al. (1989)			Wang and Kusanagi (1996)
Commelinales	Typhaceae	Typha angustifolia L.	2n = 30					Löve and Löve (1981)
Poales	Eriocaulaceae	Eriocaulon setaceum L.	n/a

Discussion

Of 45 non-hybrid aquatic monocots and two interspecific hybrids among them, more than two thirds have no chromosome variation. Meanwhile, the following nine species have infra-specific chromosome variation, i.e., , , , , , , , , and (Table 1). Among the cytologically variable aquatic monocots are , , , and , for which unique chromosome counts are obtained from each floristic region. Myanmar is known as including borders among the Indian, the Indochina, and the Sino-Japanese floristic regions (Tanaka 2010), yet in the aquatic flora, it is unknown which flora is more influenced. Future research with a focus on such species will address this issue.

is known as having numerous inter-specific hybrids, and each parental combination is varied from intra-ploidy crosses to inter-ploidy ones (Kaplan et al. 2013). The present study revealed × as another intra-ploidy hybrid of at tetraploid level.