http://chestofbooks.com/flora-plants/flowers/Illustrated-Flo...

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Note added at 12 mins (2009-10-22 17:46:59 GMT)
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1. Isoetes L. Sp. Pi. 1100. 1753

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.