Pseudo-corm 1-2 cm in diameter, 2-lobed; bud scales vestigial or lacking. Leaves 10-40, linear, 130-400 mm × 1 mm (apically)- 13 mm (at base),apex tapering to a point, yellow to midgreen, semi-circular in cross-section, abruptly ovate-oblong at the base, with broadly hyaline wing, stomata present in upper parts of the leaves. Ligule 1-3 × c. 1.5 mm, hyaline, triangular, pointed. Velum very narrow, reduced to a thin marginal ring. Sporangia 4-16 × 3-6 mm, oblong to ellipsoid, drying black and shiny. Megaspores of 2 sizes, 0.52 and 0.3 mm in diameter, dark grey, drying white, usually 3-radiate, with large warts below, granulated above. Microspores winged, reticulate.

I. alstonii is distinguished from other species in our region by its 2-lobed pseudo-corm and a sporangium that is blackish when wet.

alstonii: named after A.H.G. Alston (1902-1958), Britisch botanist specialised in African pteridophytes.

Damp pockets of soil along streams, at the edges of pools, in seasonally dry streambeds and pools, perennial in permanent mist spray of the Victoria Falls, small temporary waterholes in wooded grassland.

Africa, Madagascar.

Ethiopia, Mozambique, Namibia, Tanzania , Zambia, Zimbabwe.

Terrestrial.