KEY TO THE SPECIES

1Most pinnae of sterile lamina (except the uppermost) auriculate, margin of pinnae of sterile lamina crenate
1'Most pinnae of sterile lamina (except the uppermost) adnate to rachis or not, but not auriculate, margin of pinnae of sterile lamina (or except the apex) serrulate (sometimes towards base becoming entire or nearly so)
2Most pinnae of sterile lamina (except the uppermost) adnate to rachis or only the acroscopic side adnate
2'Most pinnae of sterile lamina (except the uppermost) cuneate, rounded, truncate, or attenuate
3Aerophores present on stipe and rachis, cross section of stipe one U-shaped vascular bundle, fronds covered with an amorphous gelatinous mucilage layer when dry.
3'Aerophores only present on base of stipe, cross section of stipe one V-shaped vascular bundle, fronds not covered with an amorphous gelatinous mucilage layer when dry
4Most pinnae of sterile lamina (except the uppermost) with acroscopic side adnate into a wide wing along rachis, dorsal side of rachis semiterete or trigonous, fertile lamina pinnate except the apex, lower pinnae shortly stalked
4'Most pinnae of sterile lamina (except the uppermost) adnate to rachis but not into a wing, dorsal side of rachis flattened or carinate, fertile lamina pinnate throughout, pinnae nearly sessile, or deeply pinnatifid and rachis slightly winged throughout
5Some pairs of lowermost pinnae of fertile lamina become aerophore-like vestiges on stipe together with aerophores, upper part of stipe tetragonal, dorsal side of the rachis of fertile lamina flattened or grooved, apex of fertile lamina terminated by a pinna conform to the lateral ones and often beaded at the base, base of middle pinnae of fertile lamina shortly stalked
5'Lowermost pinnae of fertile lamina not or gradually shortened, upper part of stipe triangular, dorsal side of rachis of fertile lamina carinate, apex of fertile lamina pinnatifid, acuminate or caudate, base of middle pinnae of fertile lamina broadly adnate
6Aerophores cushion-like, rhizome short
6'Aerophores slender, hook-shaped with pointed apex, or elongate, horn-like with blunt apex, rhizome short to c. 15 cm long, or occasionally up to 50 cm long
7Aerophores elongate, horn-like, with blunt apex, fronds not covered with an amorphous gelatinous mucilage layer when dry, paraphyses few, mostly lost, spores yellow to brown, not obviously tuberculate
7'Aerophores slender, hook-shaped with pointed apex, fronds covered with an amorphous gelatinous mucilage layer when dry, paraphyses many, spores yellow or brown, with reddish tubercles
8Sterile lamina not glaucous, herbaceous, lowermost pinnae slightly shorter or gradually shortened
8'Sterile lamina glaucous beneath, firm herbaceous or subcoriaceous, not or abruptly shortened