Sect. Cyathea
Indusium at maturity an almost flat disc, almost or quite as big as base of sorus
Indusium at maturity a disc with fairly even edge
. . . . . . . . . . C. hymenodes
Indusium at first covering sorus, apical part very thin and caducous, an irregular disc remaining on old sorus
Pinna-rachis hairy on lower surface, at least distally
. . . . . . . . . . C. sumatrana
Pinna-rachis not hairy on lower surface
. . . . . . . . . . C. excavata
Indusium otherwise or lacking
Indusium visible as a scale backing the costule, not entirely hidden by sorus
Basal scales on costae bearing some marginal setae
. . . . . . . . . . C. alleniae
Basal scales on costae without setae
. . . . . . . . . . C. borneensis
Indusium very small, hidden by sporangia
Pinnules commonly more than 20 mm. wide
. . . . . . . . . . C. incisoserrata
Pinnules commonly not more than 20 mm. wide
Paraphyses conspicuous, longer than sporangia, 2-3 cells wide at base
. . . . . . . . . . C. latebrosa
Paraphyses shorter than sporangia, slender
. . . . . . . . . . C. borneensis
Sect. Gymnosphaera
Reduced pinnae present at base of stipe, separated from normal pinnae, having segments all with a very narrow lamina, forming a wing along each side of the veins
. . . . . . . . . . C. recommutata
Reduced pinnae, separate from the rest, lacking; lower pinnae in some cases reduced gradually almost to base of stipe
Pinnules almost entire
. . . . . . . . . . C. glabra
Pinnules distinctly lobed
Scales on lower surface of costules bullate
. . . . . . . . . . C. lurida
Scales on lower surface of costules not bullate
Scales on costae bearing lateral setae; segments or lobes of pinnules rounded and subentire; sori usually not converging towards apices of segments; basal basiscopic vein from costule
. . . . . . . . . . C. glabra
Scales on costae lacking lateral setae; segments of lamina deltoid and distinctly toothed; sori converging towards apices of segments; basal basiscopic vein often from costa
. . . . . . . . . . C. gigantea
Subsect. Sphaeropteris
. . . . . . . . . . C. contaminans
Subsect. Schizocaena
Fronds simply pinnate, pinnae entire or at most serrate-crenate
. . . . . . . . . . C. moluccana
Fronds simply pinnate with deeply lobed pinnae, or bipinnate
Fronds simply pinnate with deeply lobed pinnae, the largest sometimes with free pinnules at their base
. . . . . . . . . . C. alternans
Fronds amply bipinnate
Pinnules entire or with crenate edges
. . . . . . . . . . C. alternans
Pinnules distinctly lobed
Long spreading hairs abundant on lower surface of pinna-rachis
. . . . . . . . . . C. trichodesma
Long spreading hairs lacking on lower surface of pinna-rachis
Largest pinnules with a free segment at the base; pinnules on stalks to 4 mm. or more long; texture firm
. . . . . . . . . . C. polypoda
Largest pinnules lacking a free segment at the base, almost sessile
Sori on 3-4 pairs of basal veins in each group only, not on distal veins, at maturity confluent
. . . . . . . . . . C. obscura
Sori on almost all veins, not confluent at maturity
. . . . . . . . . . C. squamulata
