Order XCIV. MarsileaceÆ.

Perennial plants, usually of small size, growing in marshes or in damp soil. Rhizome slender, creeping, rooting at the nodes. Leaves solitary or in tufts at the nodes of the rhizome, either filiform or of 4 leaflets borne at the top of a slender petiole. Sporo-carps or conceptacles globose or oblong, on short peduncles which rise from the petioles or near their bases, each sporocarp containing numerous (Marsilea) or few (Pilularia) cavities or cells, and each cell containing a group or sorus composed of macrosporangia and microsporangia. Macrosporangia containing a single macrospore; microsporangia containing numerous microspores.

A small order of 2 genera and 50 or 60 species, found in most temperate and. tropical countries. In germination a small female prothallium is developed within the macrospore, which eventually bursts, the prothallium protruding from the opening. A single archegonium is then formed on the prothallium, which is fertilised by spermatozoids set free by the bursting of the microspores,. within which a rudimentary male prothallium bearing a single antheridium has been developed.