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Diplopterygium Nakai

Terrestrial ferns of moderate to large size with scandent, thicket-forming fronds. Rhizome underground, long-creeping, dichotomously branched, a single frond at the base of each fork, protostelic, apex bearing peltate scales. Fronds of indeterminate growth, with a periodically dormant apex producing a series of pairs of primary lateral branches along the rachis, often subtended by a pair of reduced, stipule-like leaflets, the lateral branches determinate and bipinnatifid, the leaflets lobed almost to the costa, the ultimate segments oblong, margin entire or slightly toothed, the veins free, once forked, pinnately arranged each side of an obvious costule. Sori several to each lobe, attached to a small receptacle on the acroscopic branch of a vein, exindusiate, paraphyses small stellate hairs or long-fringed scales; sporangia 2-5, large sessile, annulus complete and oblique. Spores monolete or trilete, smooth and translucent.

Species in Papuasia

1a. Scales on dormant apex of rachis 1 mm wide or more, the edges fringed with spreading hairs to 0.5 mm long, or with a translucent edge bearing fine short hairs. 2
Scales on dormant apex of rachis narrower, their edges bearing short, stiff, oblique setae 5
2a. Rachis branches persistently quite covered with scales and a dense felt of stellate hairs D. bullatum
Rachis branches no quite persistently covered, nor with a felt of stellate hairs on the lower surface 3
3a. Very few persistent scales on lower surface of rachis any costae; pinnules to 22 x 3.5 cm D. longissimum
Many persistent dark scales on rachises and costae; pinnules to 12 x 2 cm D. clemensiae

4

4a. Scales on rachis apex dark brown, the edges bearing spreading hairs to 0.5 mm long; scales on rachis and costae dark brown D. clemensiae var. clemensiae
Scales on rachis apex pale, the edges very thin and very shortly fringed; scales on rachis and costae more abundant, dark at base only D. clememsiae var. membranaceum
5a. Many segments (20 or more pairs) constricted at the base and joined together by a narrow wing of even width along the costa, at the base of each pinnule 6
Few (at most 7-8) such segments on each pinnule D. sordidum
6a. Lamina rigid; segments of lamina 2.5 mm wide; scales on dormant apex uniformly dark brown D. angustilobum
Lamina thin; segments 3.5 mm wide; scales on dormant apex with dark edges D. deflexum