Centrostachys

Aquatic or subaquatic perennial herbs, prostrate to straggling or erect, usually much-branched, rooting particularly at lower nodes. Leaves opposite, entire, petiolate. Inflorescence a shortly pedunculate, elongate, bracteate spike, terminal on stem and branches; bracts persistent, hyaline. Flowers bisexual, solitary in axils of bracts; bracteoles 2, +/- circular, hyaline, falling with flower. Tepals 5, +/- spreading at anthesis, later closing together and considerably indurate at base; upper tepal narrowest and longest, 1-3-nerved. Stamens 5, shorter than perianth, shortly monadelphous at base, alternating with spathulate pseudostaminodes furnished with fimbriate dorsal scales; anthers 2-thecous. Ovary oblong in outline; ovule solitary, pendulous on curved funicle, radicle ascending; style filiform; stigma capitate. Capsule thin-walled, tightly enclosing seed, falling together with persistent perianth and bracteoles. Seed smooth, chestnut-brown; perisperm/endosperm copious.