Polystichum neocavernicola Y.Y. Liang & Li Bing Zhang, 2022

Liang, Yong-Yan & Zhang, Li-Bing, 2022, Polystichum neocavernicola (subg. Haplopolystichum; Dryopteridaceae), a new cave fern from Guangxi, China, Phytotaxa 559 (1), pp. 95-98 : 95-97

Polystichum neocavernicola Y.Y. Liang & Li Bing Zhang , sp. nov. ( Fig. 1 ).

Type:— CHINA. Guangxi: Tiandeng County, Jinjie Town , Tiannan Village , 23°20’13”N, 107°19’41”E, elev. 330 m, on walls and stalactites in a limestone cave, 8 June 2022, Yong-Yan Liang LYY2220 (holotype, CSH!; isotypes, CDBI!, IBK!, MO!) .

Diagnosis:— Polystichum neocavernicola is most similar to P. cavernicola in having the widest part of pinnae located in the middle and acroscopic margins of pinnae being repand, but the former has denser rachis scales, pinna pairs per lamina <11, lower pinnae not fertile, up to 5 sori per fertile pinna, and sori closer to the midrib, whereas the latter has sparser rachis scales, pinna pairs per lamina up to 15, all pinnae fertile, up to 8 sori per fertile pinna. and sori closer to pinna margins.

Plants perennial. Rhizome erect, short, apex densely scaly; scales loose, dark brown, lanceolate, membranous, with linear areoles, margins sparsely with shortly filiform teeth. Fronds 3.5–8.5 cm. Stipe stramineous, 8–15 mm long, 0.3–0.5 mm in diam., grooved adaxially, base sparsely covered with same scales as on rhizome apex, upward sparser. Laminae oblanceolate, 1-pinnate, 2.5–7 × 1–1.6 cm, broadest at middle, slightly narrowed toward base, apex subacute to rounded, grayish green when dried. Rachis greenish, adaxially grooved, abaxially densely covered with similar scales as on stipe but smaller. Pinnae 5–11 pairs, contiguous or slightly distant from each other, alternate, rarely basal pair opposite, ascending, sessile, thin papery, adaxially glabrous, abaxially with some brownish lanceolate and linear microscales, lower 2–5 pairs often sterile, middle pinnae 5.0–8 × 3–5 mm, oblong to obliquely rectangular, apices obtuse or rounded, bases asymmetrical and cuneate, acroscopic base obtuse-auriculate, proximal margins of pinnae truncate or slightly curved, often overlapping or parallel to rachis, distal margins with 2(–3) obtuse teeth, basiscopic margins entire, straight or slightly curved, acroscopic margins repand. Venation pinnate, indistinct on adaxial surface, distinct on abaxial surface, lateral veins ended near pinna margins, dichotomous or simple above midrib, sometimes veinlets twice forked on auricle of pinna, simple or dichotomous below midrib. Lower pinnae sterile; sori small, terminal on shorter veinlets, closer to midrib than to pinna margins, 1–3 above midrib, 0–2 below midrib; indusia small, brown, membranous, margins shallowly lacerate, deciduous when mature.

Spore morphology:—The spores are monolete, suborbicular in polar view and equatorial view. The spore size is 42–50 μm. The perispore sculpture is cristate with numerous granules ( Fig. 1 : H).

Geographical distribution: — Polystichum neocavernicola is known only from Jinjie Town, Tiandeng County in Guangxi Province, China.

Ecology:— Polystichum neocavernicola was observed to grow on walls and stalactites in a limestone cave with dim light and humid conditions.

Etymology: —From the Latin neo-, new, and cavernicola , referring to the similar morphology of the new species to that of Polystichum cavernicola .

IUCN Red List category:—CR-Critically Endangered (CR B1ab(iii) + B2 + D) following the IUCN (2017) criteria: Only one population scattering in an area of ca. 600 m 2 with about 50–100 plants in total was observed in the cave. It is not likely that the new species occurs in other caves as observed in a number of cave species of Polystichum (e.g., Zhang & He, 2009, 2010, 2011; He & Zhang, 2011, - 2012).

Additional specimens examined (paratypes): —The same place as the holotype, 9 July 2016, Yong-Yan Liang LYY1688 (CSH!, MO!, PYU!).

Taxonomic notes: —In addition to the differences between Polystichum neocavernicola and P. cavernicola outlined above, the former has shorter stipes, slightly larger ratio (ca. 1.5) of length to width of pinnae, auricles often overlapping the rachis (vs. not overlapping the rachis in P. cavernicola ). Most importantly, the two species have different perispore sculptures. The perispores of Polystichum neocavernicola have cristate sculpture with numerous granules ( Fig. 1 : H), whereas those of P. cavernicola have verrucate sculpture ( He & Zhang, 2011). In fact, perispore sculptures of both P. neocavernicola and P. cavernicola are unique in Polystichum as far as we have known.

Polystichum neocavernicola was initially considered being similar to P. fengshanense in having sterile lower pinnae, a species occurring in nine caves of two neighboring counties, Bama and Fengshan, in northern Guangxi, China ( Zhang & He, 2011; Zhang & Barrington, 2013). Polystichum neocavernicola is also found in Guangxi, and the localities of the two species are at a distance of approximately 200 km. Morphologically, P. neocavernicola has slightly larger ratio of length to width of pinnae and 2–3 teeth at the distal margins of pinnae, whereas P. fengshanense has smaller ratio (ca. 1.2) of length to width of pinnae and nearly no teeth at the distal margins of pinnae.

Polystichum neocavernicola is closely related to P. speluncicola based on our unpublished molecular data, but the two species have very different shapes of pinnae with the former being oblong-rectangular and the latter being deltoid-ovate ( Zhang & He, 2010).

Polystichum neocavernicola is an additional cave species of Polystichum in southern China endemic to a single cave with very limited number of individuals and it raises the concern of conservation.

Figures

FIGURE 1. Polystichum neocavernicola Y.Y. Liang & Li Bing Zhang.—A. Outside view of the cave where the new species was found.— B. Habitat.—C. Habit.—D. Adaxial view of frond—E. Adaxial view of lower portions of fronds.—F. Portion of abaxial pinna showing sori.—G. Abaxial view of upper portion of lamina.—H. Polar views of spores.