Small floating moss-like plants, with branching axis, covered with minute 2-lobed imbricated leaves. Sporocarps in pairs beneath the stem, very soft and thin-walled, the smaller ones acorn-shaped, containing a single macrospore, the larger ones globose, containing several microspores.
A. Carolinia'na, Willd. Somewhat deltoid in outline, much branched, of reddish aspect. Floating on quiet waters of Lake Ontario, not common.