Polystichum pingbianense Li Bing Zhang, M.Q.Han & Yan Liu, 2018

Polystichum pingbianense Li Bing Zhang, M.Q.Han & Yan Liu View in CoL , sp. nov. ( Figures 11 View FIGURE 11 , 12 View FIGURE 12 )

Type:— CHINA. Yunnan: Pingbian County, Xinxian Xiang, Shidong Village, the Stone Cave , alt. 1660 m, 23°05 ′ 18 ″ N, 103°33 ′ 26 ″ E, inside a limestone cave, 28 March 2017, Mengqi Han HMQ1320 (holotype IBK! GoogleMaps , isotype MO! GoogleMaps ).

Diagnosis:— Polystichum pingbianense is most similar to P. oblongum in having habit small (lamina <12 cm), lamina thinly papery, and pinnae not aristate-spinulose on margin and rounded at apex, but the former has petiole scales irregularly toothed on margin, a ratio of lamina length to petiole length ca. 3:1, lamina with up to 8 pairs of pinnae, and pinna margins shallowly toothed, while the latter has petiole scales fimbriate on margin, a ratio of lamina length to petiole length up to 6:1, and pinna margins coarsely toothed.

Plants perennial, evergreen, 3.2–5 cm tall. Rhizomes ascending, ca. 0.7 cm long, ca. 0.4 cm diam., with remnant bases of old petioles; roots dull brown when dried, up to 5 cm long, ca. 0.2 mm diam. Leaves in tufts, 5–12 per rhizome; petioles 0.5–1.6 cm long, ca. 0.4 mm diam., basal portions covered with scales, scales ovate-lanceolate, 2.9–4.3 × 0.9– 1.5 mm, papery, light to dull brown, edges with irregular teeth, apex caudate; distal petiole scales similar but narrower and smaller, 1.4–2.9 × 0.4–0.8 mm, membranous, margins sparsely ciliate, apex caudate. Laminae oblanceolate, 1- pinnate, 2.5–4.5 × 1–1.4 cm, apex rounded; rachises ca. 0.5 mm diam., scales subulate, lanceolate to ovate-lanceolate, light brown, 1.4–3.3 mm long including tip, 0.07–0.09 mm wide at base, margins sparsely ciliate, apex caudate. Pinnae 5–8 pairs, oblique-ovate, 0.4–0.65 × 0.3–0.45 cm, basalmost 0–2 pairs slightly smaller, basalmost pairs ca. 3/4 as large as or same as middle ones, basalmost two pairs 0.3–0.6 cm apart, middle pairs 0.4–0.5 cm apart, all pinnae papery, alternate, not overlapping rachis, basiscopic margins slightly curved, entire, acroscopic margins with obtuse teeth, basiscopic margins forming a (60–)70–80(–90)° angle with rachis, apex rounded, base cuneate and asymmetric, acroscopic sides much broader, pinna petiolues 0.2–0.3 mm long, auricles rounded at apex, abaxially with microscales, microscales narrow-type, subulate or linear, light brown, 0.3–1.3 mm long, 0.06–0.08 mm wide at base; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lowest 1–2 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, 1–3(–4) on acroscopic side of fertile pinnae, none on distal basiscopic side of fertile pinnae, ca. 1.5 mm diam., closer to pinna margins than to costa (centers of sori 0.5–1 mm from pinna margins, 1–2 mm from costa), centers 0.9–1.1 mm apart from one another; indusia rounded, light brown, ca. 4– 0.6 mm diam., margins lacerate. Spores rounded or slightly deltoid in polar view and elliptic in equatorial view; perispore sculpture reticulate with thin cristae.

Geographical distribution:— Polystichum pingbianense is only known from southeastern Yunnan, Southwest China. It is likely that it occurs only in that Stone cave in Pingbian County.

Ecology:— Polystichum pingbianense grows inside a limestone cave at an elevation of 1660 m with humid and shady conditions.

IUCN Red List category:—CR-Critically Endangered: Only one population with about 50 plants was seen in the field.

Etymology:—The species epithet is based on the Chinese pinyin, pingbian, the county name in southern Yunnan, and the Latin suffix- ense, of origin, referring to the type locality the current known distribution of the species in Pingbian County, Yunnan.

Vernacular name:—DZAEHẄ(ping bian er jue).

Notes:— Polystichum pingbianense is a small fern easily neglected in the field. In addition to the differences outlined above between P. pingbianense and P. oblongum , the former has petiole scales ovate-lanceolate, 0–2(–3) pairs of basal pinnae reduced toward lamina base, only 1–2 pairs of basal pinnae per lamina sterile, and each fertile pinna with up to 4 sori. In contrast, the latter has petiole scales lanceolate, up to 6 pairs of basal pinnae reduced toward lamina base, up to 7 pairs of basal pinnae per lamina sterile, and each fertile pinna often with 1 sorus only.