Taraxacum sect. Atrata Kirschner & Štěpánek

Kirschner, Jan & Štěpánek, Jan, 2017, A revision of Taraxacum sect. Atrata, a dandelion group centred in the Middle Asia, and the problem of Taraxacum brevirostre, Phytotaxa 305 (4), pp. 225-261 : 227-229

Taraxacum sect. Atrata Kirschner & Štěpánek in Ge et al. (2011: 314).

Type: — Taraxacum subglaciale Schischkin (1964: 743) .

Plants delicate, usually glabrous to subglabrous. Petiole usually unwinged; leaf blade usually narrow, undivided or shallowly lobed. Capitulum often nodding after anthesis. Outer phyllaries 5–15, blackish green to dark green, ± of equal length, appressed, loosely appressed, or rarely erect, narrowly lanceolate to lanceolate, usually broadest in middle, almost unbordered to bordered, margin usually glabrous but seldom sparsely minutely ciliate, apex without a horn but sometimes callose, rarely to corniculate. Ligules yellow, lilac, pinkish to light pink-purple, sometimes with different colours outside and inside. Achene (see also Figs. 10 , 11 , 12 , 18 ) usually greyish stramineous-colored brown to blackish brown, less often light stramineous-brown, (3.5–) 4–5 (–6) × 0.8–1.1 mm; body smooth or less often sparsely minutely tuberculate above, cone absent or achene body gradually narrowing into an indistinct cone, cone (when developed) broadly conical to conical and 0.4–0.8 mm; beak 1.5–5(–7) mm, ± thickened, easily breaking off. Pappus yellowish white or white, 4–7 mm.

Distribution: — Taraxacum sect. Atrata has its centre of diversity in the E. Kazakhstan and Kyrgyzstan, and in NW China (W. Xinjiang), mainly the C. and E. Tian Shan, the Ketmen Tau and the Dzhungar Alatau ranges, and its representatives reach NW. Mongolia (the UBA specimen of an unknown species of T. sect. Atrata, displayed on Fig. 1 ) in the north and Tadzhikistan, Pakistan (Gilgit) and Kashmir (Ladakh) in the southeast ( Fig. 1 ). The diversity of T. sect. Atrata probably corresponds to the geographical parthenogenesis model ( Hörandl 2006, Štěpánek et al. 2011), as there is a record of a sexual member of this section ( Zhai et al. 1997, as “ T. lilacinum ”) from the eastern part of the section’s range while the rest of the distribution area is occupied by agamospermous plants.

Its members are confined to alpine and subnival habitats, sometimes descending to subalpine grasslands, almost exclusively above 3000 m above sea level, reaching 5000 m in Pakistan. The most characteristic sites include open gravelly patches in the subnival vegetation, mosaic-like vegetation on medium old moraines, fine gravel along streams, fine wet scree and alpine low grasslands.

Reproduction: —All the plants of T. sect. Atrata studied by the present authors are agamospermous, both on the basis of the very irregular development (or total absence) of pollen, and the behaviour of plants in cultivation. However, plants morphologically similar to T. lilacinum ( Krasnov 1887: 76) Schischkin (1937: 4) were reliably reported to be sexual by Zhai et al. (1997). The status of these Xinjiang plants remains to be studied.

Comparison with similar groups: — Taraxacum subsect. Epyramidata (= T. sect. Oligantha auct., i.e., as understood by Soest in his later works, Soest 1977, see also the Discussion) is the group closest to T. sect. Atrata but differing from it in having densely hairy scapes, not numerous but imbricate (i.e., very unequal) and hairy outer phyllaries (often hairy on adaxial and/or abaxial surfaces and ciliate) of paler color, outer phyllaries with a blackish horn near apex, achene beak very thick (not caducous), and pappus fragile, easily breaking off (for details, see Table 1).

Another similar taxon, T. glabrum DC. of T. sect. Glabra Dahlst. , differs in a well-developed, distinctly narrower cone and a thin persistent beak; it also has short, unbordered erect to erect-patent outer phyllaries. As regards the SEM surface analysis (at 600 magnification), T. glabrum has irregularly distributed, only seldom well-developed appressed acute protuberances while T. chionomelas Kirschner & Štěpánek sp. nova, the SEM-analyzed representative of T. sect. Atrata, possesses the achene surface densely covered with the minute appressed acute protuberances, each about 20 μm long.

For the sake of completeness, we mention characters of T. sect. Arctica Dahlst., sometimes with representatives sympatric or parapatric to members of T. sect. Atrata in the Tian Shan. Taraxacum sect. Arctica is a diverse group, usually with densely spinulose achenes, a well developed, distinct cone (although sometimes very short), thin and persistent beak, outer bracts relatively shorter and leaves usually deeply, often also shallowly divided. The most remarkable deviation from this pattern is found in the T. kamtchaticum group, with achenes almost smooth (but with a well developed cone).

Figures

FIGURE 1. Distribution range of Taraxacum sect. Atrata.

FIGURE 10. Achenes of the members of T. sect. Atrata: A, T. alpigenum (PRA, no. det. 28132); B, T. atrochlorinum (PRA, #72); C, T. corvinum (PRA, #114/1); D, T. goloskokovii (PRA, #105/2); E, T. goloskokovii (LE, no. det. 6526); F, T. lilacinum (PRA, no. det. 28204). Scale bar = 1 mm.

FIGURE 11.Achenes of the members of T. sect. Atrata: G, T. sublilacinum (PRA, #111/2); H, T. orientali-atratum (PRA, no. det. 28210); I, T. pamiricum (PRA, no. det. 28213); J, T. pseudoatratum (LE, no.det. 7973); K, T. pseudolilacinum (PRA, #17); L, T. subglaciale (LE, no. det. 7955). Scale bar = 1 mm.

FIGURE 12. SEM photographs of an achene of T. chionomelas (beak is broken off). Scale bars:A, 1 mm; B, 0.3 mm; C, 50 μm.

FIGURE 18. Achenes of (A) T. roseiflos (PRA, no. det. 28146) and (B) T. roseolum (PRA, no. det. 28150). Scale bar = 1 mm.