The corms are very rarely found near the surface of the soil with the bases of the outer sporophylls exposed and green in colour; as a rule they are deeply buried in the earth-sometimes to a depth of 6 cm. This species is readily recognised by the 3-toothed bud-scales, narrow, opaque leaves with three conspicuous groups of strengthening fibres, poorly developed air-canals and greenish, reticulate spores. The layers of old cortex persist for several seasons, and the series of horny, 3-toothed bud-scales mark the limits of the growth of successive years.
Corms 3-lobed, harsh to the touch, up to 1-5 cm diam.; sclerised bases of sporophylls and bud-scales persisting, the latter horny and three-toothed; leaves 5-33, 1.5 to 12 cm long, firm in texture, sheathing base 1 cm or less wide, often narrowing somewhat abruptly above the level of the sporangium; lamina 0-5-1 mm wide, rounded on the back, flat or slightly furrowed above, furnished with stomata; three well-developed groups of strengthening fibres present, one at each angle of adaxial face and one at abaxial end of middle partition; air-canals poorly developed, the adaxial disappearing near the leaf apex ; ligule small, delicate in texture, elongate-triangular, sometimes cordate at base, in old leaves often imperfect through decay; velum absent; sporangia varying much in size and shape, the older megasporangia often circular in outline, the younger oval or elliptical; microsporangia conspicuously punctate, innermost often angled by pressure ; both mega- and microsporangia rounded on the back and with adaxial face flat or slightly concave, and usually bordered by a narrow rim; some of the cells of the sporangial wall conspicuously thickened, often yellowish-brown in colour; megaspores globose, from 450-590 µ in diam., basal face conspicuously reticulate, reticulations often less regular along the equatorial ridge and on the apical faces; colour of adult megaspores greenish-grey, darkening appreciably on moistening; microspores 32-36 µ long, 16-24 µ broad, brown in colour, spinulose.
Tufted geophyte with tricuspidate scales. Sporophylls 5-33, to 12 cm long, ligule small, elongate-deltate. Sporangium lacking velum.
Rhizomorph trilobed, up to 15 mm in diameter; rhizomorph-scales 4-5 mm wide, dull black usually tricuspidate. Sporohylls 5-33 in number, 15-120 mm long, abruptly dilated into a spoon-shaped or orbicular base 4-7 (-10) mm wide, often horny and persistent, with a broad scarious margin 1 mm wide which extends 10-15 mm up the leaf; apex blunt; ligule small, delicate, elongate-deltate, sometimes cordate basally. Sporangium lacking velum, variable in shape and size, the older megasporang-ium often circular, the younger oval or elliptical; microsporangium conspicuously punctate. Megaspores globose, greenish grey at maturity, darkening on moistening, distal face conspicuously reticulate, reticulations often less regular along equatorial ridge and proximal faces, c. 500 µm. Microspores brown, spinulose, 32-36 x 16-24 µm.
It occurs in ground which is marshy during the rainy season, often extends to drier areas and is then truly terrestrial. In favourable situations it grows so compactly that it may easily be mistaken for a narrow-leaved grass.
Seasonally waterlogged soils and seeps on granite outcrops, to 300 m.
This is the most abundant species of Isoetes met with on the Stellenbosch Flats.