Australian ferns & fern allies Australian National Botanic Gardens Australian National Herbarium

Isoetes L.

Terrestrial or submerged aquatic herb with several to numerous leaves, arising in an imbricate rosette from the apex of a 2 - 5-lobed, flattened, corm-like rootstock that may accumulate lobes of large quantities of dead overlapping tissue, the roots dichotomous, arising from between the lobes. Leaves sessile, simple, linear to linear-triangular, generally apically terete, flattened or angled basally, at the very base broadly winged and expanded and broadly attached to the rootstock, the mesophyll divided into 4 longitudinal, septate cavities, a single unbranched vein in the tissue between the cavities. All leaves potentially sporophylls, the sporangia very large, solitary, broadly adnate in an adaxial basal cavity, thin-walled and irregularly septate, annulus lacking, dehiscing by decay of the sporangial walls; a membranous vellum extending down from the apex and attached to the sides of the sporangial cavity, partially or entirely covering the sporangium or lacking; a small triangular ligule arising from a cavity immediately above the sporangial cavity. Sporangia of 2 types: megasporangia containing large, granular, trilete, variously sculptured or smooth megaspores; microsporangia containing minute, powdery, monolete, smooth to spinulose microspores.

Species in Papuasia