The most common representatives of this Order with us are
P. cordata, L. A stout plant growing in shallow water, sending up a scape bearing a single large arrow-heart-shaped blunt leaf, and a spike of violet-blue flowers with a spathe-like bract. Perianth 2-lipped, the 3 upper divisions united, the 3 lower spreading, the whole revolute-coiled after flowering, the fleshy base enclosing the fruit. Stamens 6, 3 of them exserted on long filaments, the rest short..
Var. angustifolia, Torr., has narrow scarcely cordate leaves.
A. Schol'lera, Schreber. Water Star-grass.
S. gramin'ea, Willd. (Heteranthera graminea, Vahl.,in Macoun's Catalogue.) A grass-like herb, wholly under water, only the small yellowish flowers reaching the surface, the latter single, from spathes. Perianth salver-shaped, regular. Stamens 3, anthers sagittate.