Plants small to medium-sized, terrestrial, or more often epiphytic, delicate ferns of wet forests. Rhizomes mostly long-creeping, filamentous or thick, occasionally with upright caudices ( Callistopteris ), hairs present or not, never scaly. Fronds spreading, upright or pendent, mostly less than 20 cm long (Vandenboschia longer). Stipes often shorter than the blades. Blades I- to 4-pinnate, lanceolate or deltate, lamina between veins one cell thick, glabrous or with simple or branched hairs (never scales), margins dentate or crenate or entire. Veins free. Sori marginal to terminal on veins of ultimate segments. Indusia cone-shaped or 2-lipped (bivalved). Sporangia borne on club-shaped receptacles in bivalved sori, or on long bristles extending from cone-shaped sori.

This family of delicate rain forest ferns contains about 600 species. The number of genera recognized is variable, from two to thirty-four. Some authors place all the species with coneshaped indusia in the genus Trichomanes and all the species with bivalved (2-lipped) indusia in the genus Hymenophyllum. In this book Copeland's (1938) work has been followed.

Represented in Hawai 'i by five genera with ten species. One species, Gonocormus prolifer, is found in Hawai 'i only on the islands of Maui and Hawai 'i, and another, Vandenboschia tubiflora, is known only from Kaua'i.

KEY TO THE GENERA OF HYMENOPHYLLACEAE IN HAWAI'I

I. Indusia (involucre) 2-lipped (bivalved); sporangia-bearing structure not protruding from indusia (Hymenophyllum s.l.) (2).

I. Indusia (involucre) cone- or urn-shaped, cut off sharply or flared at tip opening; sporangia-bearing bristle protruding from indusia (Trichomanes s.1.) (3).

2(1). Blades glabrous ............................................. . Mecodium

2. Blades slightly to very hairy ............................... Sphaerocionium

3(1). Fronds clustered on tips of solitary plants; rhizomes forming upright to decumbent caudices; stipes copiously hairy .................. Callistopteris

3. Fronds solitary, separated; rhizomes long-creeping; stipes not or sparsely hairy (4).

4(3). Rhizomes filamentous, less than 0.2 mm diam.; fronds smaller than 1 cm and fan shaped, or smaller than 6 cm and unevenly 1-pinnate to very irregularly 1-pinnate-pinnatifid, occasionally proliferous on rachises .... Gonocormus

4. Rhizomes thicker, more than 1.5 mm diam. (except in Vandenboschia draytoniana); fronds up to 40 cm or, if shorter than 7 cm, with filamentous rhizomes less than 0.2 mm diam.; fronds symmetrically and evenly 1-pinnate-pinnatisect to 3-pinnate, never proliferous .......... Vandenboschia

Reference: Copeland (1938).