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Aquatic or semi-aquatic plants. Rhizome short, erect, bearing a rosette of leaves; vascular system a dictyostele, seen in section as a ring of many meristeles, with medullary strands. Scales on rhizome apex and young fronds, thin, translucent with dark lateral cell-walls, entire, broadly ovate, more or less cordate on either side of the narrow attachment at the base. Stipes green, fleshy, with many longitudinal air-channels, rounded and ribbed on the abaxial side, flattened and smooth on the adaxial side; vascular system of 4 to many small peripheral bundles, one to each rib and several on the adaxial side also, with several smaller medullary strands. Fronds dimorphous. Sterile fronds simple to tripinnate, the venation reticulate with no free included veins. Fertile fronds more deeply dissected, with narrow lobes, their edges reflexed to meet and completely cover the lower surface; veins longitudinal, arising by branching at the base of the lobes. Sporangia globose, solitary, scattered along the veins, large with very short stalks, the annulus broad, irregular, of many slightly indurated cells. Spores pale, translucent, tetrahedral, with raised superficial lines forming a fine network of irregular long meshes.
Plants 2--120 cm. Stems 1--10 mm diam., sparsely scaly. Leaves erect. Proximal leaves broad, simple and lobed to 4-pinnate, glabrous; distal leaves finely dissected with linear ultimate segments. Sporangia nearly sessile, usually densely packed, globose. Spores tetrahedral.
Water plants; Sporangia borne singly and protected by reflexed edges of the lamina.
