极小耳蕨 ji xiao er jue

Plants evergreen. Rhizome ascending, 0.3-0.5 cm, densely covered with scales; scales brown, deltoid-ovate, 0.9-1.4 mm; roots brown when dry, up to 4 cm, ca. 0.3 mm in diam. Fronds 4-7 per rhizome, 3.3-9.5 cm; stipe green, 1.2-4 cm, 0.4-0.9 mm in diam. at middle; basal stipe scales brown, dull, deltoid-ovate, 2-2.5 × 0.5-1.2 mm, papery, margins slightly long ciliate, apices acuminate or caudate; distal stipe scales similar but narrower and shorter, varying in size, brown, dull, ovate-lanceolate, papery, margins regularly shortly ciliate, apices caudate. Lamina 1-pinnate, shiny adaxially, lanceolate, slightly contracted toward base, 2.1-6.1 × 0.85-1.25 cm at middle, acute; rachis 0.4-0.7 mm in diam. at middle, without proliferous bulbils; rachis scales brown, dull, deltoid-ovate or ovate-lanceolate, 0.5-1.3 × 0.25-0.31 mm at base, varying in size, papery, margins regularly ciliate, apices caudate. Pinnae 5-12 pairs, not overlapping, ascendant except lowest pairs, basal two pairs 2.5-6 mm apart, alternate, oblong, middle (largest) pinnae 3.2-7.3 × 2-3.5 mm, shortly stalked (stalk 0.2-0.4 mm), acroscopic base auriculate, basiscopic base cuneate and often forming an 80°-120° angle with rachis, apices acute, acroscopic margin with 1-4 teeth; abaxially scaly, adaxially glabrous; microscales on abaxial surface subulate or linear (narrow-type microscales), 0.13-0.54 mm, base 0.05-0.07 mm wide; frond texture papery; venation pinnate; midrib slightly raised abaxially, flat adaxially; lateral veins free, 2 or 3 pairs from midrib per pinna, alternate; each lateral vein again dichotomous or not, slightly raised and distinct abaxially, indistinct adaxially. Sori terminal on veins of upper pinnae, 1-3 per fertile pinna, close to pinna margin (center of sorus 0.4-0.6 mm distant from pinna margin); indusia brown, ca. 0.6 mm in diam., membranous, erose. Spores orbicular in polar view, elliptic in equatorial view, ca. 38.1 × 45.2 µm (polar axis × equatorial axis); perispore sculpturing granulate with few verrucae.

● Cave entrances; ca. 600 m. S Guizhou (Libo).

In comparison with the morphologically most similar species Polystichum minutissimum, P. perpusillum has a lamina with an acute apex and up to 12 pairs of pinnae per lamina and its rachis scales are deltoid-ovate or ovate-lanceolate, while P. minutissimum has a lamina with a rounded apex and 5-8 pairs of pinnae per lamina and its rachis scales are subulate or linear.