Halophila

Marine perennials, monoecious or dioecious, with a much-branched creeping rhizome; rhizomes bearing at nodes an abbreviated shoot and a pair of leaves, each surrounded by a basal scale; roots simple, 1 or rarely 2 from a node, densely covered with long root hairs. Leaves in pairs, petiolate, linear, lanceolate, oblong or ovate, entire or serrulate, glabrous or pubescent; midrib distinct, with a prominent lateral marginal nerve connected to midrib by many oblique secondary nerves. Flowers unisexual, usually solitary in axil of a secondary shoot, rarely 1 or 2 male and a female flower together in a spathe; spathe of 2 free, membranous bracts. Male flowers shortly pedicelled, with 3 perianth segments; stamens 3, anthers sessile, 2-4-celled, extrorse; pollen adhering to form threads; pollination hydrophilous. Female flower sessile; ovary ovoid, beaked, bearing 3 reduced perianth segments near apex; styles 2-6, linear. Fruit ovoid, rostrate, thin-walled. Seeds few to many, small, globose. x = 9.