Pleurofossa capillaris (Copel.) Nakai ex H.Ito, J. Jap. Bot.

Chen, Cheng-Wei, Lindsay, Stuart, Yong, Kien Thai, Mustapeng, Andi Maryani A., Amoroso, Victor B., Dang, Viet Dai & Huang, Yao-Moan, 2019, Clarification of Two Poorly Known Vittarioid Ferns (Pteridaceae): Haplopteris angustissima and H. capillaris, Systematic Botany (Basel, Switzerland) 44 (3), pp. 483-493 : 491

Pleurofossa capillaris (Copel.) Nakai ex H.Ito, J. Jap. Bot. 12: 408. 1936.

Epiphytic. Rhizome short-creeping, densely scaly, ca. 1 mm diam including scales, bearing fronds close together. Rhizome scales narrowly lanceolate, gradually narrowing from the base towards a long-tailed and ultimately filiform apex, 0.7–2 mm long and 0.2–0.3 mm wide (at base), clathrate, toothed at margin, the walls thickened and dentate, sometimes reddish. Fronds sessile, simple, linear, 2.7–4.5 cm long, 0.6–0.8 mm wide, widest above the middle, gradually narrowing towards both ends, apex acute or (occasionally) retuse, laminae chartaceous, glabrous, margins entire, flat on both surfaces. Venation difficult to see even with transmitted light, simple, with only a midvein (in fronds with single sori). Epidermal silica bodies linear, 0.1–0.64 mm long, present on both sides of lamina, margin lobed, ends of lobes blunt. Sori linear, uninterrupted, following the midvein, covered by a soral flap and open to one side, very rarely fertile on both sides. Soral paraphyses copious, stalks uniseriate, filiform, colourless; apical cells large, funnel-shaped, length-to-width ratio of 1.7 6 0.23, yellowish. Spores bilateral, bean-shaped, monolete, yellowish, surface smooth.

Distribution —Only known from 10 collections. The type and Chen Wade4959 are from Negros, the Philippines, seven collections are from Borneo (Sabah, Sarawak, Kalimantan, Brunei), and one collection is from an independent gametophyte population in Northern Taiwan.