Podostemaceae
A small natural order of aquatic, annual or perennial herbs, mostly very small, natives of rocky river-beds in the tropics. Flowers hermaphrodite, or, in one genus, dioecious, variously disposed, but usually inclosed in a spathaceous, marcescent involucre, which is at first closed, then bursts; perianth membranous, trifid or five-parted, or wanting; stamens definite or indefinite, free or monadelphous, erect. The plants have a distinct or branched stem and leaves, or these are confluent into broad or narrow Alga-like fronds. The 120 species comprised in the order have little or no economic or garden value; they are classified in twenty-one genera. Examples are: Apinagea, Hydrostachys, and Podostemon.