Isoetes L.
Sporangia heterosporous, 4-7 mm. long, round-oblong, deeply sunken in lf-base, chambered. Megaspores tetrahedral, white, with prominent triradiate ridges, variously marked. Microspores minute, bilateral, grey to brown, variously marked. Perennials with short, thickened, ± flattened axis; base of axis swollen, lobed, bearing ∞ forked roots; apex crowned by crowded, quill-like lvs, the tips subterete or angled, the bases broad, enclosing the sporangia. Outer lvs acting as megasporophylls, surrounding microsporophylls, innermost with abortive sporangia. About 100 spp., mainly tropical to temperate, in wet ground or aquatic. The N.Z. spp. are endemic.
