Elatinaceae

Abstract

Perennial or annual herbs of aquatic or moist terrestrial habitats, rarely (Bergia suffruticosa) suffrutescent; nodes unilacunar 1-trace (Elatine); indumentum of unicellular and multicellular multiseriate capitate trichomes, or plants glabrous; a resinous secretion widely distributed in the tissues and deposited in granular form on the surface of the stems. Leaves opposite and decussate, rarely (Elatine alsinastrum) verticillate, entire or coarsely serrate; stipules minute, scarious, distinct or interpetiolar. Inflorescences axillary, dichasial, or flowers solitary. Flowers hermaphroditic, small, actinomorphic, hypogynous, usually inconspicuous, occasionally cleistogamous; sepals 2-5(6), distinct or connate basally; petals 2-5, distinct, membranaceous, imbricate, persistent; stamens (2)3-6(-10), in 1 or 2 whorls, the outer whorl antesepalous; anthers broadly ovoid, dorsifixed, introrse, dehiscing by longitudinal slits; ovary superior, (depressed-)ovoid, (2)3-5-locular, the partitions not reaching the top of the ovary in some Bergia, stylodia 3-5; stigmas capitate, papillate; placentation axile or basal; ovules numerous, anatropous, bitegmic, weakly crassinucellar. Fruit a thin-walled septicidal capsule. Seeds ellipsoid to oblong, 0.5-1.5 mm long, with finely reticulate or smooth surfaces; endosperm reduced to 1-5 cell layers (Bergia) or 0 (Elatine); embryo straight or less often curved, filling nearly the entire seed; germination epigaeal. x = 6, 9.