The water-plantains (Alismataceae) are a family of flowering plants, comprising 19 genera (17 extant & 02 fossils) and between 85 and 95 species. The family has a cosmopolitan distribution, with the greatest number of species in temperate regions of the Northern Hemisphere. Most of the species are herbaceous aquatic plants growing in marshes and ponds. Most Alismataceae are robust perennials, but some may be annual or perennial, depending on water conditions — they are normally perennial in permanent waters, annual in more seasonal conditions but there are exceptions. The stems are corm-like or stoloniferous. Juvenile and submerse leaves are often linear, whilst more mature and emerse leaves can be linear to ovate or even sagittate. Most have a distinct petiole, with a sheathed base.