Polystichum crassirachis Li Bing Zhang, M.Q.Han & Yan Liu, sp. nov. (Figures 3, 4) Type:— CHINA. Yunnan: Qiubei County, Xindian Town, Dadong Village, in a limestone sinkhole, elev. 2000 m, 24°02 ′ 36 ″ N, 103°46 ′ 25 ″ E, 17 April 2015, Mengqi Han & Jinquan Huang HMQ094 (holotype IBK!, isotype CDBI!). Diagnosis:— Polystichum crassirachis is most similar to some individuals of P. normale Ching ex P.S.Wang & Li Bing Zhang in Zhang & Wang (2012: 250), but the former has a pinnate lamina and acute teeth on pinna margin, while the latter often has a bipinnate lamina and square teeth on pinna margin. Plants perennial, evergreen, 20–30 cm tall. Rhizomes ascending, 1.5–2.1 cm long, ca. 1.7 cm diam., with remnant bases of old stipes; roots dull brown when dried, 5–9 cm long, ca. 0.3 mm diam. Leaves in tufts, 14–20 per rhizome; petioles 10–18 cm long, 0.8–1.2 mm diam., basal portions densely covered with scales, scales lanceolate to ovate-lanceolate, 1.5–2.5 × 0.6–1.2 mm, papery, dull brown, almost entire, margins with lighter color, apex acuminate; distal petiole scales similar but narrower, 0.9–1.8 × 0.3–0.8 mm, membranous, margins irregularly erose or short-ciliate, apex long-acuminate or caudate. Laminae oblanceolate, 1-pinnate, 15–24 × 2–3 cm, apex acuminate, yellowish green when dried; rachises 0.6–0.9 mm diam., scales ovate, ovate-lanceolate, or long-lanceolate, dull brown, 0.8–1.3 mm long including tip, 0.4–0.6 mm wide at base, margins sparsely ciliate, apex long-caudate. Pinnae 22–32 pairs, deltoid, 0.8–1.4 × 0.3–0.4 cm, basalmost 3–5 pairs slightly smaller toward lamina base, nearly 2/3 as large as middle ones, 0.6–0.7 cm apart, middle pairs 0.6–0.7 cm apart, all pinnae papery, alternate, acroscopic margins and distal basiscopic margins shallowly toothed, basiscopic margins forming a nearly right angle with rachis, apex acute to obtuse, base cuneate and asymmetric with acroscopic sides being much broader, petioles 0.3–0.5 mm long, abaxially with microscales, microscales lanceolate to ovate-lanceolate, brown, ca. 0.2 mm long, 0.1 mm wide at base; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lower 3–7 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, (1–)3–7 on acroscopic side of fertile pinnae, 0–3(–4) on distal basiscopic side of fertile pinnae, ca. 1 mm diam., closer to pinna margins than to midrib (centers of sori 0.4–0.8 mm from pinna margins, 0.4–1.5 mm from midrib), centers 1.2–1.6 mm apart from one another; indusia not seen. Spores round in polar view and elliptic in equatorial view; perispore sculpture cristate and granulate. Geographical distribution:— Polystichum crassirachis is only known from southeastern Yunnan, China. It is most likely endemic to the sinkhole where it was discovered. Ecology:— Polystichum crassirachis grows inside a limestone sinkhole at an elevation of 2000 m with humid and twilight conditions. IUCN Red List category:—CR-Critically Endangered: Only one population with about 100 plants was seen in the field. Etymology:—The species epithet is based on the Latin prefix, crassi-, thick, and the Latin noun, rachis, rachis, referring to the thick rachis of the species. Taxonomic notes:— Polystichum crassirachis resembles P. subacutidens Ching ex L.L.Xiang (1994: 261) in having shallowly toothed pinna margins, but the former often has reflexed pinnae, thicker rachises, and 22–32 pairs of pinnae, while the latter has non-reflexed pinnae, thinner rachises, and 40–110 pairs of pinnae. A preliminary molecular analysis showed that the new species is most closely related with P. membranifolium Li Bing Zhang, M.Q.Han & Yan Liu (here described below) from northeastern Yunnan. However, these two species can easily be distinguished from each other in leaf texture and pinna margins (see below).

Published as part of Han, Meng-Qi, Liu, Yan & Zhang, Li-Bing, 2016, Seven new species of Polystichum (subg. Haplopolystichum; Dryopteridaceae) from southern China, pp. 201-221 in Phytotaxa 280 (3) on pages 204-206, DOI: 10.11646/phytotaxa.280.3.1, http://zenodo.org/record/13645631