Haplopteris yakushimensis C.W.Chen & Ebihara, 2014

Haplopteris yakushimensis C.W.Chen & Ebihara View in CoL , sp. nov. ( Fig. 3 View FIGURE 3 )

Type:— JAPAN. Kagoshima Pref., Island Yakushima, Nakabase River . 20 August 1982, Nakaike s.n. (holotype TNS VS-456666 !)

Differs from Haplopteris amboinensis by having chartaceous fronds with flat margins and minutely toothed rhizome scales and from Haplopteris doniana by having grooved adaxial costae and smaller (4–10 × 0.5–1.2 versus 15–20 × 1–2.5 mm) rhizome scales.

Plants lithophytic or epiphytic at the base of trees. Rhizomes short-creeping, scaly; rhizome scales clathrate, linearlanceolate, 4–10 × 0.5–1.2 mm at the base tapering to 1 cell wide at the apex, dark-brown, the edge slightly denticulate. Leaves clustered, stipes short; laminae chartaceous, linear, 15–30 × 0.5–1 cm, broadest usually near the middle, narrowed gradually towards both ends, flattened towards the base, the margins not revolute; the midribs visible and slightly grooved adaxially, abaxial surfaces with a long narrow raised ridges; veins obscure. Sorus line submarginal, superficial; sporangium stalks short, 4-celled; paraphyses 5–8 cells long, capital cell funnel-shaped, the length longer than wide. Spores monolete, oblong, 52.8 ± 4.6 µm long, surface papillate with scattered rodlets but becoming smooth when aged ( Figure 4 View FIGURE 4 ).

Distribution and habitat:—Only known from Yakushima Island, Japan, approximately 61.3 kilometers south of the Osumi Peninsula in southern Kyushu. It grows at the base of trees in lower mountain near the river at ca. 200–300 m ( Figure 5 View FIGURE ).

Etymology:—The species is named for the type locality.

Additional specimens examined:— JAPAN. Kagoshima Pref., Yakushima Island, Miyanoura . 14 August 1963, Kawabata s.n. ( TNS VS-155833 !) . Nakabase River , 4 January 2009, Oka K-090106 ( TNS VS-736790 !) . Mt. Hasadake , 24 July 1978, Kawahara s.n. ( TNS VS-583567 !) . Nakabase River , 29 December 1964, Heki 6570 ( TNS VS-789799 !) .

Conservation status:—The species is listed as a critically endangered species (CR) in the latest red list of Japan ( Ministry of Environment, Japan, 2012). Among a number of endangered species mostly due to overgrazing by sika deer ( Takatsuki 2009), this species seems to have a high risk of extinction. Formal IUCN red listing is yet to be carried out for this taxon.