Polystichum recavum H.J. Wei & Li Bing Zhang, 2018

Wei, Hong-Jin & Zhang, Li-Bing, 2018, Polystichum recavum (subg. Haplopolystichum; Dryopteridaceae), a new cave fern from Guangxi, China, Phytotaxa 374 (2), pp. 167-171 : 167-170

Polystichum recavum H.J. Wei & Li Bing Zhang , sp. nov. ( Figs. 1 & 2 ).

Type:— CHINA. Guangxi: Jinxi County, Xinjin Town, Equan Village , 23°06’13’’N, 106°22’59”E, in a limestone cave, elev. ca. 780 m, 4 Feb. 2018, She-Lang Jin & Ping Yang JSL6191 (holotype CSH! , isotypes, CDBI! , CSH! , MO! ).

Diagnosis:— Polystichum recavum is similar to P. cavernicola in having oblanceolate lamina and oblong pinnae, but the former has 4–8 pairs of lowest pinnae sterile, pinna apex often slightly concave, and auricles only slightly larger than obtuse teeth of acroscopic pinna margins, while the latter has 1–2 pairs of lowest pinnae sterile, pinna apex obtuse, and auricles distinctly larger than obtuse teeth of acroscopic pinna margins.

Plants perennial, evergreen. Rhizome short, erect, densely covered with scales. Fronds caespitose, 6–21 per rhizome, (34–)48–80(–110) mm long; stipe green, 5–19 mm long, 0.3–0.5 mm in diam. inframedial/near base, shallowly grooved adaxially, clothed with many scales at base, scales lanceolate to oblong-lanceolate, chestnut-brown to grayish brown, caudate at apex, ca. 2 × 0.4–0.5 mm, spreading, sparsely toothed on margin. Lamina oblanceolate, widest above middle, 29–93 × 6.5–12 mm, gradually narrowed toward base from below middle, apex acute or obtuse, 1-pinnate. Pinnae 10–27 pairs, subopposite to alternate, shortly stalked or subsessile, upper middle ones close to each other, sometimes contiguous or slightly imbricate, spreading, supramedial pinnae 3.5–6 × 2–3.5 mm, oblong, apex obtuserounded, with 1 or 2 coarse acute teeth, without mucro, base asymmetrical, acroscopic base wider, somewhat auriculate, proximal margins of auricles slightly curved or truncate, parallel to or slightly overlapping rachis, acroscopic margin sub-straight, repand or with shallow and coarse teeth, basiscopic base narrowly cuneate, basiscopic margins straight or sub-straight, often forming right angles or nearly right angles with rachis, entire below apex, distal basiscopic margin curved upward, upper pinnae slightly ascending, pinnae below middle gradually shortened towards base, spreading or slightly reflexed, lower pairs of pinnae often sterile, remote, 2–5(–7) mm apart from each other, oblong, subquadrangular, ovate or flabellate, lowest pairs often reduced to auricles, 0.8–3 × 0.4–2(–3) mm; venation free, visible abaxially, indistinct adaxially, pinnate, lateral veins from base upwards pinnate, dichotomous or simple above midrib, dichotomous or simple below midrib, extending into teeth but not reaching pinna margin. Frond texture papery when dried, green adaxially, pale green abaxially; rachis green, same diameter as stipe, shallowly grooved adaxially, covered with many loose scales abaxially, scales lanceolate to narrowly lanceolate, grayish brown, sparsely toothed at margin; pinnae glabrous adaxially, abaxially sparsely covered with narrowly lanceolate or hair-like scales, scales 1–1.5 mm long, grayish brown, with 1–2 teeth on margin; Sori large, ca. 1 mm in diam., medial or slightly closer to midrib than to pinna margins, terminal on shorter veinlets, 1–4 above midrib, often 1 or sterile below midrib, usually confluent when mature. indusia small, ca. 0.6 mm in diam., greyish brown, membranous, margin lacerate and ciliate, not easily seen.

Geographical distribution:— Polystichum recavum is found only in the type locality in Equan Village, Xinjin Town, Jinxi County, Guangxi Zhuang Autonomous Region, South China.

Ecology:— Polystichum recavum was observed to grow on the limestone walls near the floor under low light in a cave at an elevation of ca. 780 m.

IUCN Red List category:—The only population known is from the type locality and comprised ca. 100 plants. The cave where the new species was discovered is located in a scenic touristic area. The habitat of this species may be destroyed with the rapid development of tourism. The status of the new species should be CR—Critically Endangered category based on current information and following IUCN (the International Union for Conservation of Nature and Natural Resources) guidelines ( IUCN 2015).

Etymology:—The specific epithet is from the Latin, recavum , concave, referring to the often concave pinna apex the new species.

Vernacular name:—Mflwfi (ao yu er jue).

Taxonomic notes:—Based on its 1-pinnate lamina and lanceolate stipe and rachis scales, Polystichum recavum is obviously a member of P. sect. Haplopolystichum Tagawa (1940: 122). Morphologically, P. recavum can be easily distinguished from any species in the section by having often concave pinna apex ( Figs. 1 , 2 ). Our preliminary molecular analysis shows that P. recavum is closely-related to P. cavernicola and P. fengshanense Li Bing Zhang & H. He (2011: 859) . Indeed, P. recavum is similar to P. cavernicola in morphology, but they are distinguishable from each other (see above). Also, P. cavernicola is endemic to southern Guizhou.

Figures

FIGURE 1. Polystichum recavum H.J. Wei & Li Bing Zhang.—A. Habit.—B. Pinna.

FIGURE 2. Polystichum recavum H.J. Wei & Li Bing Zhang.—A. Outside view of the cave where the new species was discovered.—B, C. Habitat inside the cave.—D. Habit in the field.—E. Adaxial views of laminae.—F. Abaxial view of lamina.—G. Portion of abaxial surface of pinna.—H. Scales from stipes (a–c), rachis (d, e), and pinna surface (f, g).