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

Polystichum rectum Li Bing Zhang, M.Q.Han & Yan Liu View in CoL , sp. nov. ( Figures 13 View FIGURE 13 , 14 View FIGURE 14 )

Type:— CHINA. Yunnan: Malipo County, Xiajinchang Xiang, Xinyan Village , inside a limestone cave, alt. 2000 m, 23°07 ′ 17 ″ N, 104°47 ′ 35 ″ E, 31 March 2017, Mengqi Han HMQ1350 (holotype IBK! GoogleMaps ; isotypes CDBI! GoogleMaps , IBK! GoogleMaps , MO! GoogleMaps ).

Diagnosis:— Polystichum rectum is most similar to P. crassirachis Li Bing Zhang, M.Q.Han & Yan Liu in Han et al. (2016: 204) in having pinnae with acroscopic margins and distal basiscopic margins shallowly toothed, basiscopic margins forming a nearly right angle with rachis, and apex acute, but the former has pinnae often not overlapping rachis, nearly all pinnae fertile, and perispores with thick cristae, while the latter has pinnae often overlapping rachis, lowest 3–7 pairs of pinnae sterile, and perispores with thin cristae.

Plants perennial, evergreen, (7–) 11–21 cm tall. Rhizomes ascending, 1.5–3 cm long, ca. 1 cm diam., with remnant bases of old petioles; roots dull brown when dried, up to 25 cm long, ca. 0.3 mm diam. Leaves in tufts, 4–7 per rhizome; petioles 2.5–6.5 cm long, 0.7–0.9 mm diam., basal portions covered with scales, scales ovate or ovate-lanceolate, 1.8– 4.54 × 1–1.5 mm, papery, light to dull brown, edges with irregular teeth, apex caudate; distal petiole scales ovate or ovate-lanceolate, 1–2.6 × 0.5–0.9 mm, membranous, margins with irregular teeth, apex caudate. Laminae oblanceolate, 1-pinnate, 5–14.5 × 1.4–2 cm, apex rounded; rachises 0.6–0.8 mm diam., scales ovate or ovate-lanceolate, light brown, 1.4–2.6 mm long including tip, 0.5–0.9 mm wide at base, margins sparsely ciliate, apex caudate. Pinnae 14–29 pairs, deltoid-oblong, 0.6–1 × 0.3–0.4 cm, lowest 3–8 pairs reduced toward lamina base, basalmost pairs ca. 2/3 as large as middle ones, basalmost two pairs 0.4–0.6 cm apart, middle pairs 0.3–0.6 cm apart, all pinnae papery, alternate, not overlapping rachis, basiscopic margins straight, entire, acroscopic margins shallowly crenulate, basiscopic margins forming a (60–)70–90° angle with rachis, apex rounded, base cuneate and asymmetric, acroscopic sides much broader, pinna petiolues ca. 0.5 mm long, auricles acute at apex, abaxially with microscales, microscales broad-type, ovate to ovate-lanceolate, edges whitish brown, middles light brown, 0.2–1.5 mm long, 0.2–0.3 mm wide at base, margins with irregular teeth; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lowest 2–8 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, 1–9 on acroscopic side of fertile pinnae, 0–2 on distal basiscopic side of fertile pinnae, 0.9–1.5 mm diam., closer to pinna margins than to costa (centers of sori 1–1.5 mm from pinna margins, 1–2 mm from costa), centers 0.9–1.5 mm apart from one another; indusia rounded, light brown, 0.9–1.3 mm diam., margins entire or nearly so. Spores rounded or slightly deltoid in polar view and elliptic in equatorial view; perispore sculpture cristate.

Geographical distribution:— Polystichum rectum is only known from southeastern Yunnan, Southwest China. It is likely that it is endemic to the cave in Malipo County.

Ecology:— Polystichum rectum grows inside a limestone cave at an elevation of 2000 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 Latin adjective, rectum , right, referring to the often nearly right angles of pinnae forming with rachis of the new species.

Vernacular name:—ĦmNJHẄ(zhi jiao yu er jue).

Notes:— Polystichum rectum is unique in having ovate or ovate-lanceolate rachis scales and microscales (broad-type). Polystichum malipoense , P. oblongipinnarum , and P. rectum are discovered in two different caves on a same mountain in southeastern Yunnan. We strongly recommend that a nature reserve in this area bordering Vietnam be established to protect the habitats of these ferns.