Lygodium Sw.

Rhizome creeping, below ground surface, protostelic, short with fronds very close together or longer with spaced fronds, young parts densely covered with rather thick rigid multiseptate hairs, branching dichotomous; fronds borne in two rows on upper surface of rhizome, roots mainly from lower surface. Fronds of young plants erect, once or twice dichotomously branched and bearing usually palmately lobed leaflets; fronds of older plants with slender elongate twining rachises formed by a succession of very unequal dichotomies, at least the upper part of the rachis (except in L. polystaehyum) bearing two narrow wings towards the adaxial side, the surface between the wings flat or slightly raised and papillose; all branch rachises and stalks of leaflets similarly winged (Fig. 13d), the wings always interrupted to join with those of a lateral branch; primary rachis-branches always short, usually hardly developed, ending in dormant apices which are covered with hairs (such apices proliferous if the main rachis beyond them is injured), each primary branch bearing a pair of secondary branches which bear the leaflets; sterile leaflets (or their lobes) with costa and oblique lateral veins which are 1-3 times forked (anastomosing in a few species), edges entire or serrate (pinnatifid only in L. polystaehyum); fertile leaflets often with contracted lamina, bearing narrow sorophores spreading from the edges of the lamina at the ends of most of the veins; edges of sorophores serrate, the main vein in each sorophore bearing alternate short lateral veins each of which bears a single sporangium protected by a separate indusium attached along the vein and opening forwards; sporangia oblong-ovoid with a short lateral stalk, the annulus at the narrower end which is directed away from the margin of the sorophore, Splitting longitudinally when ripe; spores trilete, pale, variously sculptured on the surface, lacking perispore. Gametophyte thalloid, sometimes asymmetric; antheridia larger and more complex in structure than in most leptosporangiate ferns.