Platyhypnidium Fleischer, 1923.

Platyhypnidium riparioides is an aquatic pleurocarpous moss with nearly orbicular leaves that are denticulate to dentate over the entire margin. It could be confused only with Scleropodium, but the relevant members of that genus have the leaves much more concave and have them arranged in a julaceous manner. Note, too, that Platyhypnidium has the very Eurhynchium-like leaf cell areolation with markedly smaller distal cells relative to median cells. Scleropodium lacks this feature, and its line of somewhat inflated cells across the leaf base is hardly a feature of Platyhypnidium.
see key to Eurhynchium Etc.

Species included:
Platyhypnidium pringlei (Cardot) Broth., recognized from CA since 2004
Platyhypnidium riparioides (Hedwig) Dixon