Nephrolepis acutifolia (Desv.) H. Christ

Hovenkamp PH & Miyamoto F, 2005, A conspectus of the native and naturalized species of Nephrolepis (Nephrolepidaceae) in the world, Blumea 50, pp. 279-322 : 289-290

2. Nephrolepis acutifolia (Desv.) H. Christ - Fig. 1a; Map 1; Plate 2a

H. Christ

; Backer & Posth. (1939) 89; Copel. (1958) 189; Holttum (1968) 375; Tagawa & K. Iwats. (1985) 171; Verdc. (2001) 8. - Lindsaya acutifolia Desv. (1827) 312 . - Type: Anon. s.n. ( P? not found), Mascarenes.

Isoloma lanuginosa J. Sm. (1842b) pl. 102 . - Lindsaya lanuginosa (J. Sm.) Hook. (1846) 210 . - Type: Wallich 154 ( BM, K), East Indies.

Nephrolepis lindsayae H. Christ (1898) 837 . - Type: Schneider s.n. ( P), Sumatra . Nephrolepis niphoboloides Alderw. (1913) 18 . - Type: Koorders 61 ( BO), Java.

Nephrolepis marginalis Copel. (1917) 49 . - Type: Topping 1632 (n.v.), Borneo.

Diellia browni E.D. Br. & F. Br. (1931) 46, t. 7 . - Type: Brown 347 ( BISH n.v.), Hivaoa.

Habit, rhizome morphology. Plants forming tufts of 4-8 fronds. Runners densely branching at ± right angles, forming ʻbushesʼ around the base of the plants, 1-3 mm thick (distinctly tapering to thinner ends). Scales on runners dense (especially at the base), spreading to squarrose. Tubers absent. Fronds 150 cm long or more to 15 cm wide, stipe 15-18 cm long. Lamina base strongly reduced, tapering over 50 cm or more, basal pinnae 0.6-1 cm long, 3-3.5 cm distant, middle pinnae straight or slightly falcate. Sterile pinnae 6-8 by 1.5-1.9 cm, base slightly to strongly unequal, basiscopic base truncate, rounded or cordate, acroscopic base truncate, not auricled, margin in basal part entire, apex acute. Fertile pinnae 6-7 by 0.8-1.1 cm, different from sterile pinnae somewhat auricled as acroscopic base. Indument. Basal scales basifix or pseudopeltate, squarrose to reflexed, often inserted on a short spine, 3.5 by 0.5 mm, central part light brown, dull, hyaline margin absent, marginal glands present around the scale, margin in basal part ciliate, acumen dentate (teeth often unicellular), apex uniseriate, often somewhat zigzag. Rachis scales dense, often caducous, with a well-developed protracted acumen, spreading, hyaline or light brown, acumen ciliate, without a distinct central lamina, forming a floccose cover. Scales on lamina usually persistent, forming a tomentum similar to that on rachis. Hairs on lamina absent, costa absent. Sori marginal, linear (sometimes interrupted), not impressed. Indusium linear, attached at broad base.

Distribution - Africa (Madagascar to Ivory Coast) to Indochina (Burma, Thailand), Australia and the Pacifc (Solomon Isl., Marshall Isl., Samoa, Guam, Caroline Isl.: Ponape).

Habitat & Ecology - At low elevations (sea level up to 200 m). Usually epiphytic, often in coastal vegetation (on mangroves), also on oil palms, coconut trees, and on cliff faces.

Notes - The runners in this species are strongly branched around the erect rhizomes, with branches at angles of 60 –90º forming a dense bush around the rhizome. Otherwise, the marginal, elongated sori and the tomentose indument make this an easy species to recognize.

A form is widespread in Polynesia in which the sori are ʻdissolvedʼ into a series of separate sori on some fronds. The separate sori are lunular, with a wide sinus, but all directed towards the nearby margin, not to the apex as in N. cordifolia . In all other characters this form is identical to typical N. acutifolia . This form has been described as Diellia brownii on basis of the superficial resemblance of these sori to those in Diellia (which is otherwise completely unrelated).