Atraphaxis pungens, A. ledebourii sp. nov. and A. × uyukensis nom. provis. Our current results have shown that “ Atraphaxis pungens s.l. ” combines plants from Southern Siberia and Mongolia with three different plastid haplotypes, which replace each other in the area (Figs 2 and 8). All the plants demonstrate a great similarity in the appearance and morphology of shoots, inflorescences, perianths and fruits, so it is impossible to discriminate them. They are shrubs 15–50 cm high (Figs 9–11, Table 1) with vigorous vegetative shoots, often sylleptically branching. Second-year shoots become durable, long lasting, perennial axes bear prickly branchlets. The covering of second-year shoots is dark-gray, almost black, the cork peels off, exposing the reddish bark. Wood is pale pinkish. Second-year shoots and their branchlets bear short (5–10 cm long) axillary pale-green or creamy annual shoots. These shoots are leafy and some terminate with thyrses. Annual short generative and vegetative shoots bear small oblanceolate or spathulate leaf blades with acute or obtuse apex, gradually narrowed to the base (Fig. 9A–C; Fig. 10A, C, D; Fig. 11; Fig. 12A–B; Fig. 13A, Fig. 14D, E). Annual long vegetative shoots bear large obovate, oblongelliptic, broadly elliptic or rhomboid-elliptic leaf blades with acute or mucronate apex (Fig. 9D–F; Fig. 10B, E, F; Fig. 12C; Fig. 13B; Fig. 14A). The thyrses are usually compact, frondo-bracteose, consist of 4–7 cymes with 2–3 flowers. Perianth is yellowish-white or white, sometimes pinkish, with a very long perianth tube articulated to as long as pedicel (Fig. 12H, I; Fig. 13C; Fig. 14B, F). The epidermal cells of tepals and tube are similar (Fig. 6C–F). Atraphaxis pungens has black glossy fruits twice shorter than inner tepals of the perianth (Fig. 12J–L). Atraphaxis ledebourii has dark-brown to black fruits, 1.5 times shorter of inner tepals (Fig. 13F, G, I). In plants from Altai and Tuva, the ovary and stamens are often underdeveloped. In both species three styles are fused at the very base (Fig. 6J, K, Fig. 12D–G, Fig. 13D, E, H). In A. pungens and A. × uyukensis, stigmas are either flat and rounded, or elongated and bent out, later bevealed outward (Fig. 12G, L; Fig. 14C, G–I). In A. ledebourii from Altai Republic, the stygmas are flat and rounded (Fig. 13D), in plants from Tuva Basin and Ubsunur Basin the stygmas are globular (Fig. 6K; Fig. 13E, H). Pollen of A. pungens and A. ledebourii is tricolporate, oblong-spheroidal, elliptical in equatorial view, roundedtrilobed in polar view, with distinct, deep, and long colpi (ectoapertures). Atraphaxis pungens from Askiz, Khakassia (255) has syncolporate pollen 29.3–32.4 × 20.5–24.5 µm, A. ledebourii (sub A. pungens) from Kharalyg-Khem, Tuva (247) has the same pollen size (27.7 (25.8–31.8) × 26.3 (24.5–27.9) µm (Yurtseva et al. 2014). The pollen surface of A. pungens has striato-perforate ornamentation with distinct, protruding, intensively branching and merging striae and grooves with 2–7 pits or perforations in a row (Fig. 7C). Atraphaxis pungens 304 from Kartushibinskii ridge has spherical pollen grains 30 µm in diameter with abnormal flat ridges and slit-like grooves (not shown). Thus, A. pungens and A. ledebourii do not show reliable morphological characteristics which let to clearly distinguish them. Due to high morphological similarity of A. pungens and A. ledebourii, their putative hybrid A. pungens × A. ledebourii (243) from Kaa-Khem village (Tuva, Kyzylskii Raion) does not differ from the parents. This hybrid has larger leaves at vegetative shoots, larger perianths and fruits (Fig. 10F) The reciprocal hybrid A. ledebourii × A. pungens 318 from Hangay, Mongolia, has black, shiny fruits common for A. pungens. Three specimens of A × uyukensis (241, 301, 311) from Kara-Khaak and the Uyuk ridge, Tuva, combine plastid haplotype U and ITS ribotypes P2 and P2del of A. pungens (303, 316, 317, 319) (Figs 1, 3). The sample (301) from Kara-Khaak, Tuva (Fig. 9F) resembles other specimens of A. pungens in the appearance, long vegetative shoots, broadly elliptical leaf blades, perianth, and black glossy fruits (Fig. 14A–C). The samples 241 and 311 (Fig. 11) resemble the samples A. pungens (184, 192, 304) from Kartushibinskii ridge (Fig. 9A–C) in the appearance, oblongoblanceolate leaf blades of short generative and vegetative shoots, small thyrses, and yellowish perianths (Fig. 14D–F). Their stygmas are flat, which is a characteristic of A. pungens (compare Fig. 12D–F and Fig. 14G–I).

Published as part of Yurtseva, Olga V., Vasilieva, Natalia V., Kostikova, Vera A. & Samigullin, Tahir H., 2022, A broadly sampled 3 - loci plastid phylogeny of Atraphaxis (Polygoneae, Polygonoideae, Polygonaceae) reveals new taxa: III. A. kuvaevii and сryptic species in A. pungens from Southern Siberia and Northern Mongolia, pp. 13-63 in Phytotaxa 566 (1) on pages 25-33, DOI: 10.11646/phytotaxa.566.1.2, http://zenodo.org/record/7103418