Submerged, amphibious or uliginous plants with a cluster of elongated awl-shaped leaves rising from a more or less 2-3-lobed fleshy short stem, the leaves with or without peripheral bast-bundles, with or without stomata, bearing a small membranous organ (ligule) above the base. Sporanges sessile in the excavated bases of the leaves, orbicular or ovoid, the sides more or less covered with a fold of the inner side of the leaf-base (velum). The sporanges of the outer leaves usually contain spherical, mostly sculptured macrospores, those of the inner ones contain minute powdery usually oblong microspores. [Name Greek, taken from Pliny, apparently referring to the persistent green leaves.]

The family consists of the following genus only.

About 60 species, widely distributed. Besides the following 2 are known from the southern United States, 7 from the Pacific Coast and 2 from Mexico. Owing to their aquatic habitat and apparently local distribution, these plants are popularly little known. The spores mature in summer and autumn. Type species: Isoetes lacustris L.

Leaves without peripheral bast bundles.

Leaves without stomata; plants submerged.

Leaves stiff and erect.


I. inacrospora.

Leaves slender and mostly recurved.

Leaves about 1/2" in diameter.


I. Tuckermanii.

Leaves at least 1 1/2" in diameter.


I. hieroelypliica.

Leaves with stomata; plants partially submerged, or emersed.

Leaves green.

Macrospores armed with spines.


I. Brounii.

Macrospores without spines, merely crested or warted.

Leaves 2'-3' long; macrospores less than 55ou in diameter.


I. saccharata.

Leaves 4'-8' long; macrospores about 600 u in diameter.


I. riparia.

Leaves reddish, or rarely olive green.


I. foveolata.

Leaves with stomata and bast bundles.

Aquatic, but usually inhabiting the water's edge, sometimes completely emersed.

Leaves from 12'-30' long; macrospores with convolute labyrinthine ridges.


I. Eatoni.

Leaves shorter; macrospores otherwise marked.

Bast bundles only 4, except in some forms of /. Engelmanni,


Macrospores coarsely crested.


I. Dodgei.

Macrospores merely reticulated.


I. Engelmanni.

Polygamous; microspores rare.


I. Gravesii

Bast bundles 4, with extra ones near periphery.


I. melanopoda.

Terrestrial, or rarely growing near water's edge.


I. Butlcri.

1 Isoetes L Sp Pi 1100 1753 118