MARSILEACEAE (Pepperwort Family)

Plants perennial, heterosporous. Stems thin rhizomes, widely creeping. Leaves varying in size due to different water levels. Sporangia enclosed in highly modified leaves (sporocarps), these globose or orbicular to oval in outline and flattened, turning brown and hard at maturity, single or grouped, stalked. Megasporangia several per sporocarp, each containing 1 megaspore. Microsporangia several per sporocarp, each containing 20–64 microspores. Spores trilete, the surface variously ornamented to smooth, the megaspores 0.3–0.7 mm in diameter, with a small, dome-shaped papilla, the microspores 50–80 mm. Gametophytes endosporic within the megaspore walls.

Three genera, about 50 species, nearly worldwide.

The sporocarps of this family are complex structures that are highly modified leaf blades containing several sori. They are not homologous to the sporocarps of the Azollaceae, which are derived from modified individual sori.

Leaf morphology is highly variable in the family as a result of fluctuating ecological conditions. All of the species can function as submerged or emergent aquatics. Petiole length can vary with the relative water depth at the time of leaf development, as the leaf elongates to the water's surface. In some species, sporocarps are only produced when the plants are emergent at or near the water's edge.

Species of Marsileaceae are mostly colonizers of open, aquatic habitats. As such, populations may appear and disappear sporadically as succession occurs in the ponds and lakes whose shores they inhabit.