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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

1a. Plants terrestrial; leaves thick and leathery, +/- triquetrous distally, c. 3-5 mm wide at the middle; megaspores psilate, 800 um or more in diameter; Mt Carstenz... I. hopei
Plants aquatic; leaves thin and +/- fleshy, terete distally, 1-3 mm wide at the middle; megaspores finely rugulose, or reticulate, or irregularly and deeply reticulate and/or warty, 500-700 um in diameter... 2
2a. Megaspore ornamentation finely and irregularly rugulose, appearing almost smooth at low magnification; leaves generally 2-3 mm wide at the middle; Mt Wilhemina (Mandala) and Star Mts... I. habbemensis
Megaspore ornamentation reticulate, of even or irregular relief; leaves generally 1-3 mm wide at the middle... 3
3a. Megaspore ornamentation shallowly or moderately pronounced reticulate of even relief lower than or equal to that of the trilete ridge; leaves 2-3 mm wide at the middle... 4
Megaspore ornamentation deeply reticulate generally of uneven relief as high as the trilete ridge, often appearing warty; leaves 1-2 mm wide at the middle; Owen Stanley Range... I. neoguineensis
4a. Megaspore ornamentation of shallow relief less than the trilete ridge; Mt Giluwe... I. stevensii
Megaspore ornamentation as pronounced as the trilete ridge; Mt Saruwaged... I. "frigida"