Taraxacum xanthellum Kirschner & Štěpánek, 2025

Kirschner, Jan, Štěpánek, Jan & Buryy, Vladimir V., 2025, Towards a revision of Taraxacum sect. Borealia (Compositae, Crepidinae) in Siberia and the continental Far East, with special reference to the dandelions of the Altai and Kamchatka, Phytotaxa 679 (1), pp. 1-147 : 19-23

2. Taraxacum xanthellum Kirschner & Štěpánek , sp. nov.

Type:—[ RUSSIA, Altai Republic] USSR, Sibiria austro-occid., montes Altaj, pars Ajgulakskij chrebet, distr. Usť-Ulagan , in pratis haud procul a lac. Mjortvyje Ozera, ad clausam mont. Ulaganskij Pereval, ca. 1850–1900 m, 2 Jul 1988 , J. Kirschner , cultivated as T 173 ( PRA, no. det. 35985, holotype) .

Etymology:—Yellowish.

Diagnosis:—Inter species cum stigmatibus luteis vel subluteis, species phyllariis adpressis, paucioribus, concoloribus, acheniis ± brevibus, pyramide anguste cylindrica longa insignis.

Plants not tall but subrobust, usually to 12–14 cm tall. Petiole light purplish, deeper so abaxially, winged to broadly winged, arachnoid, mainly along mid-vein, plant base without tunic. Leaves deep green, ± arachnoid along the light purplish mid-vein, oblanceolate in outline, usually 7–9 × 2–3 cm, some leaves undivided, denticulate to sinuate-lobulate, most of the middle leaves pinnatilobed to pinnatipartite; terminal segment relatively small, broadly triangular, acute to subobtuse, with convex to straight, entire margins; lateral segments approximated, in 5–7 pairs, broadly deltoid to broadly triangular, patent to subrecurved, straight, subconcave to subconvex, usually entire (only basal segments often with minute teeth), proximal margin ± straight or subconvex, entire; interlobes almost absent (lobes ± folded and ± overlapping at base), or short and broad. Scapes ± brownish green, arachnoid, distally densely arachnoid, ± overtopping leaves, at least some leaves growing from outside the leaf rosette. Capitulum ± bright yellow, 3.5–4.0 cm wide. Involucre blackish olivaceous-green, ca. 8–9 mm wide and rounded at base. Outer phyllaries (9) 10–13 (14), loosely appressed to appressed, ± not imbricate, ovate-lanceolate to narrowly lanceolate, usually 7.0–9.5 × 2.3–3.3 mm, surface deep to blackish olivaceous-green, often with ± black longitudinal venation, border narrow, often almost invisible and greenish-membranous, sometimes whitish-membranous, 0.2–0.3 (–0.4) mm wide, margin glabrous or very sparsely ciliate distally, apex with black or blackish-purple horns, usually 1.5–2 mm long; inner phyllaries 12–13 mm long, later to 18 mm long, dark corniculate. Outer ligules flat, faintly striped light greyish-purplish or with 2–4 very light greyish lines, or almost unstriped, teeth light grey-purple, inner ligule teeth yellow to dirty yellow. Stigmas pure light yellow. Pollen present, pollen grains irregular in size. Achenes light greyish stramineous-brown, (3.6–) 3.7–3.9 (–4.3) × ca. 1.0 (–1.2) mm, body subdensely covered with distinct, relatively short erect-patent spinules in upper 1/3, subabruptly narrowing into a subcylindrical to cylindrical cone (0.7–) 0.8–0.9 (–1.1) × 0.3–0.4 mm, beak thin (ca. 0.1 mm), (9–) 10–11.5 mm long, pappus 6–6.5 mm, white. – Agamospermous. – Fig. 4F , 6 , 7 .

Diagnostic notes:—Among the species with yellow or only very indistinctly discoloured stigmas, T. xanthellum is distinct in having a relatively thin, ± cylindrical cone usually 0.8–0.9 mm long. Outer phyllaries are ± appressed (and therefore differ from T. platycranum ), not numerous (9–14), which is a number usually exceeded in T. compitale and T. macroceras , and usually the paler border is lacking or indistinct, narrow (developed in the other members of this group). In comparison with taxa with known achenes, T. xanthellum has a longer cone.

Distribution:—This distinctive species has a large distribution range, with disjunct localities. It is known from numerous sites within a macrolocality of the Ulaganskiy Pereval, the Central Altai, and from the western shore of Lake Baikal, Irkutsk Region.

Specimens examined:—[ RUSSIA, Altai Republic] Usť-Ulagan District, range of Aigulakskii Khrebet, meadows in the vicinity of Myortvye Ozera ( Lakes ) near the pass Ulaganskiy Pereval , 1850–1900 m, 2 Jul 1988, J. Kirschner, cultivated as JŠ 3365 ( PRA, no. det. 36747). – Ibidem, cultivated as T 173 ( PRA, no. det. 36758). – Ibidem , cultivated as T 174 ( PRA, no. det. 36756). – Ibidem , cultivated as T 175 ( PRA, no. det. 36755). – Ibidem , cultivated as T 178 ( PRA, no. det. 36753). – Ibidem , cultivated as T 156 ( PRA, no. det. 36751). – Ibidem , cultivated as T 186 ( PRA, no. det. 36749). – [ RUSSIA] S. Siberia , Irkutsk region, Baikal Lake , in the vicinity of Listvyanka , pastures along the shore of Lake Baikal , near the origin of Angara R., 26 Oct 1985, J. Kirschner & J. Štěpánek, cultivated as JŠ 2712 ( PRA, no. det. 37770) .

Figures

FIGURE 4. Details of involucres of Taraxacum species from the Altai, in alphabetic order. A, T. peracre (PRA, T 55); B, T. perdecorum (PRA, no. det. 35992); C, T. peschkovae (PRA, no. det. 35855); D, T. seminudum (PRA, JŠ 2597); E, T. tortisquameum (PRA, no. det. 35983); F, T. xanthellum (PRA, T 173); G, T. xiphodon (PRA, T 162). Scale bars: D = 2 mm; A–C, E–G = 5 mm.

FIGURE 6. Taraxacum xanthellum. A, general habit (PRA, no. det. 35985, holotype); B, achenes (PRA, from specimens cultivated as JŠ 3365).

FIGURE 7. Taraxacum xanthellum. The holotype. Photo M. Hladík.