Polystichum alluvium Li Bing Zhang, N.T.Lu & Yi F. Duan, 2017

Polystichum alluvium Li Bing Zhang, N.T.Lu & Yi F. Duan View in CoL , sp. nov. ( Fig. 1 View FIGURE 1 ).

Diagnosis:— Polystichum alluvium is somewhat similar to P. lanceolatum ( Baker 1880: 494) Diels (1900: 193) in having small habit and subcoriaceous pinnae, but the former has oblanceolate laminae with basal pinnae strongly contracted toward the lamina base, deltoid-ovate and sessile pinnae, and very short or no spinules on acroscopic pinna margins, while the latter has lanceolate laminae with basal pinnae not contracted toward the lamina base, oblong and petiolate pinnae, and long spinules on acroscopic pinna margins.

Type:— CHINA. Guizhou: Liuzhi Tequ, Xinyao Xiang , in a cave, 26°14’20’’N, 105°22’21”E, elev. 1410 m, 17 June 2016, Li Bing Zhang, Yi-Fan Duan, Ngan Thi Lu & Xin-Yuan Miao 9328 (holotype CDBI! GoogleMaps ; isotypes CDBI! GoogleMaps , MO! GoogleMaps , herb. Pei-Shan Wang! GoogleMaps ).

Plants perennial, evergreen, 4–8 cm tall. Rhizomes short, nearly erect, 5–12 mm long, ca. 7 mm in diam., with remnant bases of old stipes; roots unseen. Leaves fastigiate, 8–14 per rhizome; stipes 5–12 mm long, 0.2–0.5 mm in diam., basal portions densely covered with scales; basal stipe scales lanceolate to ovate, 1.1–1.8 × 0.3–0.5 mm, chartaceous, composed of multiple cells, brown to dark brown in color, edges with lighter color and almost entire, apex acuminate; distal stipe scales similar but narrower, 0.4–1.5 × 0.2–0.4 mm, membranous, margins short-ciliate, apex longacuminate or caudate. Laminae oblanceolate, 1–pinnate, 2–6.5 × 0.7–1.7 cm, apex acute, green when dried; rachises 0.1–0.2 mm in diam.; rachis scales subulate to lanceolate, brown, 0.3–2 mm long including tip, 0.05–0.55 mm wide at base, margins sparsely ciliate, apex acuminate to caudate. Pinnae 10–18 pairs, deltoid-ovate, 2.75–7.25 × 2–3.25 mm, basalmost 2–4(–6) pairs much smaller toward lamina base, ca. 1/6 as large as middle ones, 0.2–3.25 mm apart, middle pairs 2.5–4.25 mm apart; all pinnae papery, alternate, basiscopic margins entire, acroscopic margins almost entire or very shallowly crenulated and teeth with or without short spinules, basiscopic pinna margins forming an angle of (45–)90–110(–120)° with rachis, apex acuminate to apiculate, base cuneate to obtuse and asymmetric about midribs with acroscopic sides being much broader, sessile, abaxially with microscales; microscales subulate, brown, ca. 0.5 mm long, 0.025 mm wide at base, adaxially glabrous; abaxially with visible venation and somewhat obscure adaxially, lateral veins free, single or once forked. Basal pinnae fertile; sori terminal on lateral veins, (0–)1–3(–4) on acroscopic side of fertile pinnae, 0 or 1 on distal basiscopic side of fertile pinnae, ca. 1 mm in diam., closer to pinna margins than to midrib (centers of sori 0.13–0.5 mm from pinna margins, 0.2–1.25 mm from midrib), centers 0.6–1.25 mm apart from one another; indusia peltate, 0.4–0.8 mm in diam., membranaceous, yellowish brown, erose on margin.

Geographical distribution:— Polystichum alluvium is only known inside an anonymous cave located in Xinyao Xiang (Township), Liuzhi Tequ, Guizhou Province. Our extensive fieldwork in Guizhou in 2016 did not find additional occurrence of the species.

Ecology:— Polystichum alluvium was observed to grow at the entrance of a medium-sized kart cave at an elevation of 1410 m with shady and relatively humid conditions. The cave is about 20 × 30 m in size.

IUCN Red List category:—The only population is known from the type locality and comprised about 50 plants in a very small alluvial area of ca. 5 × 10 m, affected by seasonal flooding at the bottom of the cave. The status of the new species is clearly CR (Critically Endangered) based on current information and following the guidelines of IUCN Red List Criteria ( IUCN 2015).

Etymology:—From the Latin prefix alluvium-, alluvial, referring the seasonal flooding habitat of the new species.