fern - any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores

clover fern, pepperwort - any of several water ferns of the genus Marsilea having four leaflets

pillwort, Pilularia globulifera - European water fern found around margins of bodies of water or in wet acid soil having small globose sporocarps

regnellidium, Regnellidium diphyllum - small latex-containing aquatic fern of southern Brazil

floating-moss, Salvinia auriculata, Salvinia rotundifolia - free-floating aquatic ferns

Azolla caroliniana, Carolina pond fern, mosquito fern, floating fern - small free-floating aquatic fern from the eastern United States to tropical America; naturalized in western and southern Europe

Ceratopteris pteridioides, water sprite, floating fern - aquatic fern of tropical America often used in aquariums

Ceratopteris thalictroides, floating fern - pantropical aquatic fern