Stipa baxoiensis Y. Zhang & W. L. Chen, 2023

Zhang, Yue, Zhang, Xie-Yong, Zhang, Chao, Chen, Wen-Li & Zhu, Shi-Xin, 2023, Stipa baxoiensis (Stipeae, Poaceae), a new species from Qinghai-Tibet Plateau, China, Phytotaxa 597 (4), pp. 280-286 : 281-284

Stipa baxoiensis Y. Zhang & W. L. Chen , sp. nov. ( Figs. 1 , 2 )

Type:— CHINA. Tibet: Baxoi County, Bangda town, Ye-la Mountain , 30.13°N, 97.277°E, in shrubs on rocky slopes, alt. 4238 m, 15 July 2022, C. Zhang 3 (holotype: PE, No. 2714338; isotypes: PE, No. 2714339, No. 2714340, No. 2714341) .

Diagnosis:— Stipa baxoiensis is close to S. subsessiliflora ( Ruprecht 1869: 35) Roshevitz (1915: 50) in the contracted and suberect panicles, but differs mainly by its densely hirsutulous leaf sheath and adaxial surface of leaf blade, and the scabrous middle awn segment.

Description:— Perennial, densely tufted, intravaginal, not rhizomatous. Culms 20–45 cm tall, erect, glabrous, 1–2-noded. Sheaths of basal leaves 5–7 cm, sheaths of cauline leaves 10–15 cm, longer than internodes, both densely hirsutulous. Basal ligules 1.5–2 mm, membranous, lanceolate, apex acuminate, margin ciliate, with dense pubescence dorsally, ca. 0.1 mm; cauline ligules 1–1.5 mm, slightly shorter than those of basal leaves, apex obtuse, margin ciliate. Blades of basal leaves 2–15 cm, blades of cauline leaves 4–7 cm, both convolute, ca. 1 mm in diam., densely hirsutulous on both surfaces, hairs ca. 0.2 mm and ca. 0.1 mm long on abaxial and adaxial surface respectively. Panicles contracted, 8–15 cm long, 1–1.5 cm wide, exserted from uppermost leaf sheaths; branches straight, with 5–10 spikelets. Spikelets yellowish green; lower glume 7–9 mm, much longer than floret, lanceolate, 5–veined, apex acuminate; upper glume 6–9 mm, equal or slightly shorter than lower glume; lemma 5–7 mm, terete, pilose on abaxial surface, with overlapping margins; callus ca. 1 mm, pungent; awn 15–22 mm, with joint at the base, 2-geniculate, lower awn segment 5–6 mm, with 1.5–2 mm long hairs, middle awn segment 3–4 mm, scabrous, bristle 8–10 mm, straight, glabrous or slightly scabrous; palea 5–7 mm, subequal to lemma, membranous, 2-veined, usually hairy between veins; lodicules 3, lanceolate, membranous, 1.5–2 mm; anthers 3, dark purple, 3–4 mm, glabrous at apex; styles 2.

Distribution and habitat:— Stipa baxoiensis is distributed in Bangda town, Baxoi County, Qamdo city, Tibet. The new species is currently known only from the eastern QTP, near the Nujiang River Basin, and grows in shrubs on rocky slopes at elevations from 4200–4400 m above sea level ( Fig 2 : B).

Phenology:— Flowering and fruiting from July to October.

Etymology:— The specific epithet refers to the type locality, Baxoi county (E QTP, China).

Additional specimens examined: — CHINA. Tibet: Baxoi County, Bangda town, Ye-la Mountain , 30.143°N, 97.2881°E, in shrubs on rocky slopes, alt. 4403 m, 6 September 2021, X. Y. Zhang & W. H. Li 440 ( PE, No. 2641506) .

Taxonomic notes:— Tzvelev (1974, 1976, 1993) recognized nine sections of Stipa from the Soviet Union mainly based on the characteristics of glumes, lemmas, awns and ligules. Emphasizing the awn characteristics, Kuo (1982) divided Chinese Stipa into five sections. He combined sect. Pseudoptilagrostis Tzvelev (1974: 13) with sect. Regelia based on the character combination of awn 2–3 cm long, 2-geniculate, and column plumose and included five species and two varieties in the section. Recently, Nobis et al. (2015, 2016) accepted two varieties of Stipa aliena Keng (1941: 74) , and published a new species Stipa dickorei . Up to now, a total of seven species and four varieties was included in section Regelia mainly distributed in western China: S. regeliana Hackel (1884: 130) , S. dickorei , S. basiplumosa Munro ex Hooker (1896: 229) , S. subsessiliflora , S. baxoiensis , S. aliena var. aliena , S. aliena var. macrocarpa ( Martinovský 1970: 163) Nobis (2015: 238) , S. penicillata Handel-Mazzetti (1936: 226) var. penicillata and S. penicillata var. hirsuta P. C. Kuo & Y. H. Sun (1984: 89) ( Kuo & Sun 1982, Nobis et al. 2015, Nobis et al. 2016).

The new species Stipa baxoiensis belongs to sect. Regelia due to its 2-geniculate awns, plumose columns and glabrous bristles ( Kuo & Sun 1982). It is similar to S. subsessiliflora in contracted panicles but differs in the hirsutulous (vs. glabrous) leaf sheath and abaxial surface of leaf blades, glumes 7–9 mm (vs. 6–8. 5 mm) long, the middle awn segment scabrous (vs. with 1–1.5 mm long hairs), and panicles exserted from uppermost leaf sheaths (vs. enclosed by uppermost leaf sheaths at base) ( Fig 2 : C–E).

In sect. Regelia , both the new species and S. penicillata var. hirsuta have much hairy leaf sheaths and blades, but the later differs by its lax panicles, panicle branches flexuous and with cushions in axils, and longer hairs on middle awn segment ( Fig 2 : C–E). A detailed comparison among the new species and all the other members of the sect. Regelia in China is given in Table 1 as well.

The morphological character of densely haired leaves is seldom happened in Stipa and possibly an adaptation strategy to the cold or arid environment at QTP ( Fig 2 : B). Stipa zhadaensis and S. arabica Trinius & Ruprecht (1842: 77) var. turgaica ( Roshevitz 1949: 21) Tzvelev (1976: 584) are another two taxa from QTP with much haired leaves, but they are members of the section Barbatae Junge (1910: 130), with awns plumose throughout their length ( Kuo & Sun 1982).

Figures

FIGURE 1. Stipa baxoiensis. A. Habitat; B. Habit; C. Leaf blades; D. Roots; E. Ligule and parts of leaf sheath and blade; F. Anthers and part of spikelets; G. Glumes and floret; H. Lemma and callus; I. Palea.

FIGURE 2. Stipa baxoiensis and allied species. A: Holotype of S. baxoiensis; B: Distribution map; C: Panicles; D: Leaf blades; E: Glumes, florets, middle awn segment. C–E: From left to right are S. baxoiensis, S. subsessiliflora and S. penicillata var. hirsuta.