Polystichum serratissimum Li Bing Zhang, M.Q.Han & Yan Liu, 2016

Han, Meng-Qi, Liu, Yan & Zhang, Li-Bing, 2016, Seven new species of Polystichum (subg. Haplopolystichum; Dryopteridaceae) from southern China, Phytotaxa 280 (3), pp. 201-221 : 217

Polystichum serratissimum Li Bing Zhang, M.Q.Han & Yan Liu , sp. nov. ( Figures 13 , 14 )

Type:— CHINA. Yunnan: Yanshan County, Ashe Town, Ashe Xiaozhai, ca. 1.5 km southwest of the village, elev. 1570 m, 23°37 ′ 46 ″ N, 103°42 ′ 50 ″ E, inside a limestone cave, 20 April 2015, Mengqi Han & Jinquan Huang HMQ122 (holotype IBK!, isotypes CDBI!, MO!).

Diagnosis:— Polystichum serratissimum is most similar to P. pseudoacutidens Ching ex W.M.Chu & Z.R.He (2000: 257) in having coarsely toothed pinna margins, but the former has oblong pinnae and acute pinna apices, while the latter has deltoid pinnae and acuminate pinna apices.

Plants perennial, evergreen, 36–46 cm tall. Rhizomes ascending, 1.5–2 cm long, ca. 0.9 cm diam., with remnant bases of old stipes; roots dull brown when dried, 3–6 cm long, ca. 0.3 mm diam. Leaves in tufts, 14–21 per rhizome; petioles 9–14 cm long, ca. 1 mm diam., basal portions densely covered with scales, scales ovate-lanceolate, 2–2.8 × 1–1.5 mm, papery, dull brown, margins with lighter color and almost entire or with short outgrowths, apex caudate; distal petiole scales similar but narrower and shorter, deltoid or ovate-lanceolate, 0.6–1 × 0.3–0.5 mm, membranous, margins irregularly erose or short-ciliate, apex long-acuminate or caudate. Laminae oblanceolate, 1-pinnate, 24–32 × 3.7–4.5 cm, apex acuminate, green when dried; rachises 0.7–1 mm diam., scales deltoid, subulate or ovate-lanceolate, dull brown, 1–2.5 mm long including tip, 0.2–0.9 mm wide at base, margins sparsely ciliate, apex long-caudate. Pinnae 18–24 pairs, oblong, 1.6–2.4 × 0.6–0.8 cm, basalmost 2–4 pairs slightly smaller toward lamina base, nearly 2/3 as large as middle ones, 1.3–1.5 cm apart, middle pairs 1–1.1 cm apart, all pinnae papery, alternate, basiscopic proximal margins entire, acroscopic margins and basiscopic distal margins serrated or biserrated, teeth 0.8–1.5 mm deep and sharp on tip, basiscopic margins forming a 60–120° angle with rachis, apex acute, base cuneate and asymmetric with acroscopic sides being much broader, petioles ca. 1 mm long, abaxially sparsely with microscales, microscales deltoid or subulate, brown, 0.3–0.5 mm long, 0.5–0.7 mm wide at base, margins with irregular outgrowths; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lower 0–3 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, 7–13 on acroscopic side of fertile pinnae, (2–)3–6 on distal basiscopic side of fertile pinnae, ca. 1.5 mm diam., closer to pinna margins than to midrib (centers of sori 1.2–1.6 mm from pinna margins, 0.6–4 mm from midrib), centers 1.5–1.8 mm apart from one another; indusia rounded, ca. 0.7 mm diam., lacerate. Spores round in polar view and elliptic in equatorial view; perispore sculpture cristate and granulate.

Geographical distribution:— Polystichum serratissimum is only known from southeastern Yunnan, Southwest China. It is likely that it occurs only in that limestone cave.

Ecology:— Polystichum serratissimum grows inside a limestone cave at an elevation of 1570 m with humid and shady 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, serrati-, serrated, and -ssimum, most, referring to the serrated pinna margins of the species.

Taxonomic notes:— Polystichum serratissimum is a very distinct species by having coarsely toothed pinna margins, which is reminiscent of P. formosanum Rosentock (1915: 338) and P. pseudoacutidens . The similarity among these three species is, however, homoplastic.

Figures

FIGURE 13. Polystichum serratissimum.—A. Inside view of the sinkole where the new species was discovered.—B, C. Habitats and plants.—D–F. Portions of abaxial laminae.—G. Portions of stipes showing scales.—H. Equatorial view of spore under SEM.

FIGURE 14. Polystichum serratissimum.—A. Habit.—B. Portion of abaxial lamina.