Rhizome filiform; stipites rather distant to close-set. Stipes filiform, 5-30 mm. long, not winged. Rhachis filiform, narrowly winged in upper part. Lamina 2-8 cm. long, pale green, pellucid, narrow-ovate to lanceolate-oblong, pinnate; pinnae rather distant to approximate, pinnatifid; final segs oblong, teeth falcate to almost straight. Sori on short lateral segs near axils in upper part of lamina, free to very slightly immersed. Indusium 1·5-2 mm. long, suborbicular, much wider than seg., 2-valved nearly to base; valves obovate to suborbicular, spinulosely toothed on margins. Receptacle included to barely exserted.

n = 22

This is the most easily distinguished of the New Zealand species, lacking a wing on the lower portion of the rachis. (In some very small specimens the rachis may be winged to its junction with the second to lowest pair of pinnae.) It is, however, most variable in appearance. Holloway (1923) commented that it is "extremely variable in its frond form but from the fact that different forms are not found intermixed and that they are characteristic of slightly different stations it would seem that they are the expression of small differences in the environment". A number of these forms are illustrated. A common form is shown in Fig. 3 c, d with typically bilateral branching of the pinnae, deeply toothed indusial valves, and a rachis winged less than halfway down. Fig. 3 e illustrates a form that is usually sterile and found in deep shade. The branching of the pinnae is unilateral and the rachis is winged nearly ¾ of the way to its base. The form shown in Fig. 3 f, g seems common in damp forests, particularly in the South Island. All these forms, with toothed indusia, wings confined to the upper part of the rachis, and solitary sori, are easily distinguished from H. peltatum. The lack of a wing on the stipe and all of the rachis is the best character distinguishing H. revolutum from H. cupressiforme (Fig. 2 a-e). The indusial margin, nearly entire to crenulate or denticulate in the latter and denticulate in the former, is often a useful additional character. The difference in the teeth of the lamina margin (often falcate in H. revolutum; mostly straight in H. cupressiforme (Tindale, 1963)) is not evident in New Zealand specimens.