Hydrostachyaceae Engl.

Leaves emergent or sometimes floating, often fern-like, borne in a rosette on the rhizome, developing when the water is low, dilated and ligulate at the base, at first small and entire, becoming large, entire, lobed or 2–3-pinnate, the petiole, rhachis and subdivisions covered with emergences of very diverse shape. Flowers unisexual in dense spikes (synflorescence polytele), sometimes appearing precociously, usually when water low, each flower borne in the axil of a bract consisting of a distal and proximal part, the latter usually termed the spur (éperon). Sepals and petals absent. The ? flower is reduced to a single stamen; anther with 2 divergent thecae dehiscing longitudinally; pollen in tetrads. The ? flower reduced to a unilocular but 2-carpellate ovary; placentas 2, parietal with numerous anatropous tenuinucleate unitegmic ovules; styles 2, glabrous, erect or divergent. Fruit a small capsule enclosed by the bract, opening by 2 equal valves along the median suture, many-seeded, bearing the persistent styles. Seeds ovoid, very light; endosperm cellular, divided into 3 parts but transitory, soon used by the developing embryo and ± nil in ripe seeds. Partly submerged aquatic dioecious (but in one species monoecious, and another monoecious or dioecious) herbs with tuber-like rhizomes, sometimes stoloniferous, the roots attached to rocks in waterfalls and rapidly running water