Underestimated diversity in one of the world's best studied mountain ranges: The polyploid complex of Senecio carniolicus (Asteraceae) contains four species in the European Alps.

Senecio carniolicus (Asteraceae) is an intricate polyploid complex distributed in the European Alps (di-, tetra- and hexaploids) and Carpathians (hexaploids only). Molecular genetic, ecological, and crossing data allowed four evolutionary groups within S. carniolicus to be identified. Here, we establish that these four groups (two vicariant diploid lineages, tetraploids and hexaploids) are also morphologically differentiated. As a consequence, we draw taxonomic conclusions by characterizing four species, including the more narrowly circumscribed S. carniolicus (lectotypified here), the taxonomically elevated S. insubricus comb. nov. (lectotypified here), and the two newly described species S. disjunctus and S. noricus.

Introduction

The European Alps are among the world’s best-explored mountain ranges with respect to their plant diversity, but additions to the inventory of Alpine plants still occur due to the discovery of species hitherto unknown from the Alps—e.g. Saxifraga carpatica Sternberg (1831: 32; published in Schneeweiss 1998) or Carex glacialis Mackenzie (1910: 244; published in Blanchemain )—or of so far overlooked species such as Pinguicula poldinii J. Steiger & Casper (published in Casper & Steiger 2001: 28), Saxifraga styriaca Köckinger (2003: 82) and Alyssum neglectum Magauer, Frajman & Schönswetter (published in Magauer : 500). Further additions to the Alpine flora resulted from disentangling the components of polyploid complexes composed of lower-ploid parental entities and their higher-ploid derivatives such as in the group of Cardamine amara Linnaeus (1753: 656), Achillea pratensis Saukel & R. Länger (1992: 160) or Gymnadenia conopsea (Linnaeus 1753: 942) R.Br. in W.T.Aiton (1813: 191) s.l. (Marhold 1992, Saukel & Länger 1992, Marhold ).

Senecio carniolicus Willdenow (1803: 1993) has only recently been identified as an intricate polyploid complex (Suda , Sonnleitner ). Within the long-recognised Senecio sect. Jacobaea (Miller 1754: 667) Gray (1821: 469), a monophyletic group of mostly western Eurasian species (Pelser , 2003), the species belongs to the informal Incani-clade containing mountain species distributed from the Spanish Sierra Nevada to the Carpathians. Delimitation and taxonomic status of S. carniolicus as well as its evolutionary relationships to close relatives have been discussed controversially. Although sometimes treated as subspecies of Western alpine S. incanus Linnaeus (1753: 869), (e.g., by Chater & Walters 1976, Aeschimann , Fischer ), molecular data consistently support the distinctness of S. carniolicus (Pelser , Escobar García ).

Senecio carniolicus is widely distributed in the Eastern European Alps and the Carpathians. The Alpine distribution area ranges from the Alpi Lepontine and the Prealpi Luganesi at the border between Switzerland and Italy to the easternmost central Alps of Austria (Suda , Sonnleitner ). It occurs almost exclusively on siliceous bedrock (Ellenberg 1996) and thrives in a variety of alpine habitats, such as grasslands and dwarf shrub communities, stabilized scree slopes and rock crevices (Pignatti 1982), moraines and pioneer swards (Beger in Hegi 1928) as well as wind-exposed fellfields with strong freeze-thawing dynamics (Franz 1986). The altitudinal distribution ranges from timberline up to the nival zone (Reisigl & Pitschmann 1958).

In its previous circumscription S. carniolicus was considered a morphologically variable species, especially with respect to the leaf shape and indumentum. Plants from the western border of the species’ range with deeply divided and at least underneath densely hairy leaves have been described as S. carniolicus var. insubricus Chenevard (1906: 367). Later, this taxon was usually treated as S. incanus subsp. insubricus (Chenevard) Braun-Blanquet (1913: 300). It was commonly hypothesized that this entity, whose leaves possess some resemblance to those of S. incanus, might represent a hybrid between these two taxa (Chenevard 1906) with hypothetical intermediate ploidy (Ozenda ). However, molecular data unambiguously show that this entity is most closely related to S. carniolicus with no traces of introgression by S. incanus (Escobar García ). Additional infraspecific taxa of S. carniolicus-under S. incanus subsp. carniolicus (Willd.) Braun-Blanq. (1913: 300)—have been distinguished by Beger in Hegi (1928), who mentioned three, often coexisting formae: S. incanus f. incanescens A.Kern. ex Beger in Hegi (1928: 767) with greyish-tomentose indumentum, S. incanus f. glabrescens Hausm. ex Beger in Hegi (1928: 767) with glabrous to sparsely hairy leaves, and S. incanus f. pinnatilobatus Bornm. ex Beger in Hegi (1928: 767) with deeply incised leaves often with secondary lobes.

The presence of ploidy level variation in S. carniolicus (Schönswetter , Suda , Hülber ) suggests that the morphological types might not merely be habitat-induced modifications of the same species, but instead correspond to different cytotypes. In the Alps, three main cytotypes (di-, tetra- and hexaploids) are found, while in the Carpathians only hexaploids occur (Suda ). Cytotypes co-occur in major parts of the distribution area (Suda , Sonnleitner ) sometimes within a few decimetres (Hülber , 2015). Nevertheless, intermediate ploidy levels were only found in ca. 1% of individuals in a comprehensive sample of about 5000 individuals (Sonnleitner ), indicating strong crossing barriers under natural conditions. This is supported by molecular genetic differentiation among cytotypes (Hülber , M. Winkler et al. unpubl.) and, within the diploids, between two longitudinally vicariant groups (Escobar García ); by poor seed sets and very low hybrid viability in crosses between (eastern) diploids and polyploids, though not between polyploids (Sonnleitner ); and by microhabitat differentiation between the three main cytotypes (Sonnleitner , Hülber ). Consequently, there is strong evidence that S. carniolicus in its present taxonomic circumscription contains four ecologically differentiated, genetically distinct, and partly reproductively isolated groups: western diploids, eastern diploids, tetraploids and hexaploids.

Here, we establish that these four groups are morphologically differentiated. As a consequence, we draw taxonomic conclusions by formally describing two new species and by redefining, at the species level, the circumscriptions of S. carniolicus subsp. carniolicus and S. carniolicus subsp. insubricus. In addition, we provide diagnostic characters and the geographic distribution of these four species as well as a determination key.

Material and Methods

We sampled S. carniolicus in its current wide circumscription on 28 collecting sites evenly distributed over its distribution area (collecting sites 1, 2, 4, 10, 15, 18, 20, 21, 22, 23, 26, 40, 41, 46, 63, 64, 65, 66, 72, 77, 79, 80, 81, 87, 92, 96, 97, 100 in Sonnleitner ), collecting one flowering shoot and one vegetative rosette per individual. As the collection was done without prior knowledge of the cytotype, sample sizes differ across the sites. Plant material was preserved in 75% alcoholic aqueous solution until preparation. Additionally, several specimens were taken from each population to be deposited in the herbarium WU. All individuals were ploidy-checked (Sonnleitner ). From the alcohol-preserved material, one fully developed rosette leaf and one cauline leaf from the middle of the flowering stalk were pressed and dried. The number of ray and disk flowers of one fully anthetic capitulum was counted and flowers were mounted on sticky paper. Involucre width and length as well as the height of the flowering shoot and of the synflorescence were measured directly on the alcohol material. Values presented in the species descriptions correspond to the 10% and 90% quantiles, supplemented by extreme values scored on specimens listed under “Additional specimens examined”.

Results and Discussion

The polyploid complex of S. carniolicus is an example of underestimated species diversity in the generally well-explored european Alps. It comprises a group of closely related taxa that are not only genetically and ecologically distinct, but exhibit also clear morphological differences. Our field experience showed that flowering individuals can be assigned to one of the four groups with high accuracy. Morphological separation of the two diploid taxa is mainly based on higher indumentum density and a lower number of flowering heads per synflorescence in western diploids, and coincides with complete geographical separation and the absence of recent gene flow (Escobar García ). Polyploids differ from diploids in a taller growth and a longer corolla of ray flowers. In comparison to hexaploids, tetraploids are characterized by a stronger degree of the leaf dissection, i.e., deeply incised rosette leaves and presence of distinct secondary lobes in stem leaves.

The congruence of morphological differences with genetic divergence (Escobar García , Hülber , Winkler et al. unpubl.), ecological differentiation and the presence of crossing barriers (Schönswetter , Hülber , Sonnleitner , 2013) highlight the distinctness of these evolutionary lineages. On this basis we propose splitting S. carniolicus into four taxa, which together constitute the S. carniolicus agg. Separation at the species level seems most appropriate, because the four entities meet several requirements of different species concepts. Most importantly, reproductive isolation between diploids and polyploids is almost complete. No intermediate cytotypes were encountered in the broad area of co-occurrence of western diploids and hexaploids (Sonnleitner ), and artificial crossings between eastern diploids and polyploids failed almost completely (Sonnleitner ). Tetra- and hexaploids hybridize upon hand pollination (Sonnleitner ), but intermediate cytotypes are nevertheless rare in nature (Sonnleitner ). This is likely due to ecological differentiation particularly in areas of sympatry of tetraploids and hexaploids (Hülber ). Specifically, tetraploids are most common on northern slopes, which are rarely occupied by hexaploids, and—in contrast to the other three entities—also extend to intermediate to slightly basic soils. Therefore, polyploids usually do not form mixed populations, but only narrow contact zones in areas of ecological overlap (Hülber ). The four entities can therefore be regarded as functional biological species, which hybridize only occasionally. Occupation of different ecological niches or “adaptive zones” (Van Valen 1976), as demanded by the ecological species concept (Coyne & Orr 2004), further supports distinction at the species level.

Two taxa are newly described here, and S. carniolicus subsp. insubricus is raised to the species level with a new circumscription to comprise all diploids west of river Isel and south of river Drau. Application of the name S. carniolicus is restricted to the hexaploid cytotype. Due to the lack of morphological synapomorphies of the genus Jacobaea Miller (1754: 667), which was recently resurrected based solely on molecular evidence (chloroplast and ITS data; Pelser , 2007, Nordenstam & Greuter in Greuter & Raab-Straube 2006), we choose to make taxonomic changes and descriptions under Senecio Linnaeus (1753: 866), which is in accordance with recent taxonomic treatments (Pawłowski & Jasiewicz 1971, Aeschimann , Fischer , Calvo ).

Taxonomic treatment

Senecio carniolicus aggregate

Perennial, herbaceous hemicryptophytes with short creeping rhizome, erect to ascending, lanulose stems, and alternate, spirally arranged leaves forming a basal rosette. Flowering stems with petiolate cauline leaves, which are reduced in size towards the apex. Capitula arranged in terminal cymose corymbs, heterogamous, radiate and yellow-flowered. Peduncules with one to three bracteoles in the upper part, lanulose. Involucre campanulate, with supplementary bracts; supplementary bracts few to several, narrowly linear to filiform; involucral bracts uniseriate, linear-lanceolate to narrowly oblong, attenuate, sparsely to densely tomentose, with dark reddish to blackish apex and somewhat longer bristles on the margin. Ray flowers female, fertile; tube cylindrical, lamina strap-shaped, apically three-toothed; disc flowers hermaphroditic; corolla narrowly tubular, gradually widening upwards, five-lobed, glabrous. Style branches apically obtuse with short sweeping-hairs. Pappus bristles simple, united in a basal ring, minutely barbellate with short acute teeth, off-white to yellowish or fawn-coloured, persistent. Achenes oblong, slightly flattened, longitudinally grooved, light brown, glabrous.

Four species can be distinguished

1. : 1993) ≡ Jacobaea carniolica (Willdenow) Schrank (1814: 316) ≡ Senecio incanus subsp. carniolicus (Willdenow) Braun-Blanquet (1913: 300) ≡ Jacobaea incana subsp. carniolica (Willdenow) B.Nord. & Greuter in Greuter & Raab-Straube (2006: 712).

Type:—sine loco, Herbarium Willdenow, B 15778/3! (lectotype, designated here); syntypes: sine loco, Herbarium Willdenow, B 15778/1; sine loco, Herbarium Willdenow, B 15778/2!; “Judenburger-Alpe, Im August 1811”, Sieber, Herbarium Willdenow, B 15778/5! The fifth syntype (“In alpibus Tolmiensibus”, Herbarium Willdenow, B 15778/4!) consists of plants with leaves densely hairy on both sides. This contradicts the diagnosis of Willdenow (“[…] Folia […] supra viridia subtus albido-pubescentia, juniora alba […]”). This specimen, which may have formed the basis for Willdenow’s epithet, is excluded from the original material because it cannot be the basis for the validating description; this specimen belongs to S. insubricus.

Description:—Plants (3)7–17(27) cm tall. Rosette leaves (4)5–10.5(13.5) cm long, petiolate, leaf blade (1.5)2–4.9(5.1) cm long, elongate-ovate to obovate in outline, with cuneiform base, shallowly lobed to dentate or almost entire, lobes usually only as long as wide, undivided, only rarely with smaller secondary lobes; young leaves densely tomentose and therefore greyish, upper leaf surface glabrescent with age, often subglabrous. Middle cauline leaves (1.3)2.7–4.8(6.2) cm long, sparsely tomentose to subglabrous. Capitula (5)6–14(23). Involucre (2.3)2.9–4(5.5) mm wide. Ray flowers (2)3–6(7), corolla (5.5)7–11.2(12.6) mm long. Disc flowers (5)7–14(16), corolla (4.6)5.6–7.4(8.2) mm long. Pollen grains (28)31–40(43) μm. Hexaploid (2n = 6x = 120). Figs 1A, 2A, 4A.

FIGURE 1

Iconography of Senecio carniolicus (A), S. insubricus (B), S. noricus (C) and S. disjunctus (D). Drawings: R. Flatscher.

FIGURE 2

Representative shapes of rosette leaves (left) and cauline leaves (right) of Senecio carniolicus (A) and S. noricus (B). Drawings: R. Flatscher.

FIGURE 4

Representative individuals of Senecio carniolicus (A, Almerhorn, population 58 from Sonnleitner ), S. insubricus (B; Plose, population 46), S. noricus (C; Bretthöhe, population 80), and S. disjunctus (D; Bretthöhe, population 80). Note the characteristic differences in indumentum density and leaf dissection as well as in the number of capitula per synflorescence. Photographs: M. Sonnleitner.

Ecology:—Alpine meadows, preferentially swards dominated by Carex curvula Allioni (1785b: 264), with high vegetation cover on siliceous substrate, ca. 1750–3150 m.

Distribution:—The species is distributed in the central Eastern Alps (Fig. 5A) from Rätische Alpen/Alpi Retiche and Bergeller Alpen/Monti della Val Bregaglia (Lombardia, Italy and Graubünden, Switzerland), Albula-Alpen and Silvretta (Graubünden, Switzerland as well as Vorarlberg and Tirol, Austria) eastwards to Gleinalpe (Steiermark, Austria). In addition, it occurs in high ranges of the Carpathians (Poland, Slovakia, Romania). It remains to be investigated if the morphologically slightly divergent plants from the Southern Carpathians (Romania) should be recognised as a separate entity.

FIGURE 5

Distribution of the four species of the Senecio carniolicus agg. in the Eastern Alps based on Sonnleitner ; S. carniolicus (A), S. insubricus (B), S. noricus (C) and S. disjunctus (D). Morphometrically evaluated populations are marked with a black dot.

Etymology:—The species is named after the historical Duchy of Carniola (Herzogtum Krain, Vojvodina Kranjska) within the Habsburg Empire, which comprised large parts of present-day Slovenia as well as southernmost Kärnten (Carinthia) and Steiermark (Styria). It should be noted that S. carniolicus does not occur in that area (see above under “Type”).

2. (Chenevard) R. Flatscher, Schneew. and Schönsw., comb. et stat. nov. ≡ Senecio carniolicus var. insubricus Chenevard (1906: 367) ≡ Senecio incanus subsp. insubricus (Chenevard) Braun-Blanquet (1913: 300) ≡ Jacobaea carniolica subsp. insubrica (Chenevard) Pelser (2006: 5) ≡ Jacobaea incana subsp. insubrica (Chenevard) B. Nord. & Greuter in Greuter & Raab-Straube (2006: 712).

Type:—[SWITZERLAND. Ticino/Tessin:] “Alpi di Pietra Rossa obenher Colla im Canton Tessin [Alpi di Pietra Rossa above Colla in the canton Tessin/Ticino], 20 July 1869”, H. Siegfried, ZT 37371! (lectotype, designated here); syntype: “Camoghe”, O. Heer, ZT 37373!

Description:—Plants (3)4–9(15) cm tall. Rosette leaves (2.2)2.6–6.5(8.7) cm long, petiolate, leaf blade (1)1.5–2.5(3.5) cm long, ovate in outline, usually with truncate to rounded base, lobed to deeply incised. Middle cauline leaves (1.1)1.6–3.4(5.7) cm long. All leaves densely and persistently tomentose on both sides, whitish, rarely single leaves glabrescent. Capitula 2–5(6). Involucre (2.2)2.9–4.4(4.6) mm wide. Ray flowers (3)4–8, corolla (5)6–8.5(9.6) mm long; disc flowers (10)12–22(25), corolla (4.3)4.6–6.1(6.4) mm long. Pollen grains (26)27–32(37) μm. Diploid (2n = 2x = 40). Figs 1B, 3A, 4B.

FIGURE 3

Representative shapes of rosette leaves (left) and cauline leaves (right) of Senecio insubricus (A) and S. disjunctus (B). Drawings: R. Flatscher.

Ecology:—Rock crevices and other habitats in the alpine to subnival zone with shallow soil layer on siliceous bedrock, very rarely also on carbonates (most prominently, the disjunct population in the Karawanken/Karavanke thrives on dolomite); ca. 1850–3150 m.

Distribution:—The species occurs in the western part of the central Eastern Alps (Fig. 5B) from the Alpi Lepontine (Ticino, southern Switzerland/Italy) to the Isel Valley (Osttirol, Austria); disjunct occurrences are in the southeastern Alps in the Karnische Alpen/Alpi Carniche (Austria, Italy) and the Karawanken/Karavanke (Kärnten, Austria/Gorenjska, Slovenia).

Etymology:—The species takes its epithet from a historical region in Northern Italy between Lago di Como and Lago di Garda. The name of the region is connected to the ancient tribe of the “insubres” mentioned by several ancient Roman authors. Chenevard first used this epithet in his description of a novel variety of S. carniolicus. He considered this taxon a possible hybrid of S. carniolicus with the vicariant S. incanus, with a narrowly endemic distribution confined to the Alpi Lepontine and Alpi Orobie.

3. R. Flatscher, Schneew. and Schönsw., sp. nov.

Type:—AUSTRIA. Salzburg, Ankogelgruppe, Hohe Tauern, Großer Hafner, 47°4‘9‘‘N, 13°23‘45‘‘E, ca. 2890 m, 13 August 2008, P. Escobar García (holotype WU 0080559!; isotypes WU, W, IB, GZU, Z, and BOZ).

Description:—Plants (2.7)3.8–8.1(9.3) cm tall. Rosette leaves (1.8)2.5–6(8) cm, petiolate, leaf blade (1)1.5–2.5(3) cm long, ovate in outline, usually with truncate to rounded base, lobed to deeply parted, sparsely hairy, greyish-green. Middle cauline leaves (1.1)1.4–3.3(3.6) cm, petiolate. Capitula (4)6–13(16). Involucre (2)2.2–3.2(3.7) mm wide. Ray flowers 3–7(8), corolla (4.3)4.6–6.7(7.5) mm long. Disc flowers (8)10–14(16), corolla (3.9)4.4–5.9(7.2) mm long. Pollen grains (23)25–31(35) μm. Diploid (2n = 2x = 40). Figs 1C, 2B, 4C.

Diagnosis:—Senecio noricus differs from the other members of the S. carniolicus agg. in the following characters: leaves not persistently densely hairy on both sides, therefore not whitish (vs. S. insubricus); plants usually 4–8 cm tall, pollen grains (23)25–31(35) μm in diameter, growing in open, exposed habitats (vs. S. disjunctus and S. carniolicus).

Ecology:—The species thrives in open, exposed habitats, such as alpine fellfields, on siliceous bedrock, and occurs from ca. 2000 to 3000 m.

Distribution:—The species is endemic to Austria and occurs in the eastern part of the central Eastern Alps (Fig. 5C) from the Isel Valley (Osttirol) to the easternmost Niedere Tauern (Seckauer Alpen, Steiermark, Austria).

Etymology:—The species takes its name from the province Noricum in the Ancient Roman Empire, which comprised the current Austrian federal states Ober- and Niederösterreich, Kärnten and Steiermark as well as parts of Tirol.

4. R. Flatscher, Schneew. and Schönsw., sp. nov.

Type:—AUSTRIA, Steiermark, Rottenmanner Tauern, Großer Bösenstein, 47°26‘24‘‘N, 14°24‘48‘‘ E, ca. 2110 m, 27 July 2008, P. Escobar García (holotype WU 0080561!, isotypes WU, W, IB, GZU, Z and BOZ).

Description:—Plants (4.6)5.3–16.1(19.2) cm tall. Rosette leaves (2.5)3.5–8.5(11) cm long, petiolate, leaf blade (1.6)2–4(5) cm long, ovate in outline, usually with truncate base, deeply lobed to pinnatisect, lobes usually more than two times longer than wide, usually with one or more small distinct secondary lobes, glabrous in individuals occupying the eastern partial area, sparsely hairy to subglabrous in individuals from the western partial area. Middle cauline leaves (1.6)2.1–4.5(7.4) cm long. Capitula (4)6–15(21). Involucre (2.5)2.8–4(4.9) mm wide. Ray flowers (3)4–7(10), corolla (3.9)6.1–8.8(9.4) mm long. Disc flowers (8)10–18(21), corolla (2.5)4.9–6.9(7.2) mm long. Pollen grains (26)28–36(37) μm. Tetraploid (2n = 4x = 80). Figs 1D, 3B, 4D.

Diagnosis:—Senecio disjunctus differs from other members of the S. carniolicus agg. in the following characters: leaves not persistently densely hairy on both sides, therefore not whitish (vs. S. insubricus); plants usually 5–16 cm tall, pollen grains (26)28–36(37) μm in diameter, usually growing in habitats with dense vegetation cover (vs. S. noricus); rosette leaves deeply incised, lateral lobes usually longer than wide, always divided (vs. S. carniolicus).

Ecology:—Alpine meadows and dwarf shrub communities, with a tendency towards north-exposed slopes, sometimes also on stony, more shallow soils than S. carniolicus; usually on siliceous bedrock, but more frequently found on intermediate to slightly basic substrates than the other species; ca. 1870–3080 m.

Distribution:—The species occurs in two disjunct distribution areas (Fig. 5D); the western partial range spans from the Alpi Bergamasche to the Ortler/Ortles and Adamello massifs (Südtirol/Trentino/Brescia, Italy; Graubünden, Switzerland) and the eastern partial range extends from the easternmost Hohe Tauern eastwards (Salzburg/Kärnten/Steiermark/Austria). It remains to be investigated based on a broader sampling whether the morphological differences between individuals from the two partial distribution areas are constant enough to allow for the taxonomic recognition at the subspecific level.

Etymology:—The epithet refers to the distribution pattern of the species, whose range is split into two disjunct partial areas.

Determination key to the S. carniolicus aggregate and its closest relatives

This key includes all Alpine species of the Incani-clade sensu Pelser with the exception of the morphologically very divergent S. abrotanifolius Linnaeus (1753: 869). Thus, in addition to the S. carniolicus aggregate this key also contains S. incanus, which was formerly often considered conspecific with S. carniolicus (e.g., Chater & Walters 1976, Aeschimann , Fischer ), and the morphologically clearly distinct and thus taxonomically uncontroversial Western Alpine species S. persoonii De Notaris (1844: 229) and S. halleri Dandy (1970: 625) (≡ S. uniflorus (Allioni 1773: 70) Allioni (1785a: 200), non Retzius (1783: 42).