by Nathaniel Lord Britton & Addison Brown, An Illustrated Flora of the Northern United States… (1913)
“ Floating annual plants with slender stems bearing rather broad 2-ranked leaves, these finely papillose on the upper surface. Sporocarps globose, depressed, 9-14-sulcate, membranous, arranged in clusters, 1 or 2 of each cluster containing 10 or more sessile megasporanges, each containing a single megaspore, the others containing numerous smaller globose pedicelled microsporanges with very numerous microspores. ”
