Adiantum spp.
Family: Pteridaceae
Project: Southwest Biodiversity Consortium
Plants terrestrial or on rock. Stems short- to long-creeping or suberect, branched; scales deep tawny yellow to dark reddish brown [black], concolored or bicolored, linear-lanceolate to lanceolate, margins entire, erose-ciliate, or minutely dentate. Leaves monomorphic to somewhat dimorphic, densely clustered to closely spaced [distant], 15--110 cm. Petiole chestnut brown to dark purple or blackish, with single groove adaxially, glabrous, hispid, or strigose, with 1 or 2 vascular bundles. Blade lanceolate, ovate, trowel-shaped, or fan-shaped, 1--4(--9)-pinnate proximally, membranaceous to papery, both surfaces commonly glabrous (2 species with scattered hairs), adaxially dull or shiny, not striate; rachis straight or flexuous. Ultimate segments subsessile to short-stalked (stalks terminating in cupulelike swelling at base of pinna in A . tenerum ), round, fan-shaped, rhombic, or oblong, 3--29 mm wide; base truncate to cuneate, free from costa; stalk dark, often lustrous; fertile segments with marginal lobes recurved to form false indusia. Veins of ultimate segments conspicuous, free, ± dichotomously forking near base and well above segment base [anastomosing in a few tropical species], parallel distally. False indusia light gray-green or brown to dark brown, narrow, 0.6--1 mm wide, marginal, concealing sporangia until sporangia dehisce. Sporangia submarginal, borne along or sometimes also between veins on abaxial surface of false indusium, paraphyses and glands absent. Spores yellow or yellowish brown, tetrahedral-globose, trilete, rugulate to rugose or tuberculate, equatorial ridge absent. x = 29, 30. Most diverse in Andean South America, Adiantum is primarily a tropical genus; of the nine species occurring in the flora, A . melanoleucum , A . tenerum , and A . tricholepis are strictly subtropical. Adiantum hispidulum occurs only as an escape from cultivation. The genus is absent from dry areas in the interior of the continent.
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