Herbs [subshrubs], annual [short-lived perennial], synoecious [polygamous]. Leaves opposite [whorled], simple; stipules present; petiole present or absent; blade margins entire or serrulate; venation pinnate. Inflorescences axillary, usually cymes or flowers solitary, sometimes 2[–3]-flowered clusters. Flowers bisexual [pistillate]; perianth and androecium hypogynous; hypanthium absent; sepals 2–5, distinct or connate basally; petals (0 or) 2–5, distinct; nectary absent; stamens [0–]1–10, distinct, free; anthers dehiscing by longitudinal slits; pistil 1, 2–5-carpellate, ovary superior, 2–5-locular, placentation axile; ovules 2–33[–44] per locule, anatropous; styles 2–5, distinct; stigmas 2–5, capitate. Fruits capsules, dehiscence septicidal or irregular. Seeds 2–33[–44] per locule.
Nearly worldwide in temperate and tropical regions.
Genera 2, species ca. 50 (2 genera, 11 species in the flora).
The affinities of Elatinaceae have long been uncertain; relationships with Caryophyllaceae and Clusiaceae have been proposed (G. C. Tucker 1986). Recent molecular work, combined with a review of morphology, indicates a sister relationship with Malpighiaceae (C. C. Davis and M. W. Chase 2004; K. Wurdack and Davis 2009).
|1||Sepals 5, carinate; petals 5; inflorescences usually cymes, rarely solitary flowers, pedicels present; plants glandular-pubescent; stems solid or pithy.||Bergia|
|1||Sepals 2–4, not carinate; petals (0 or) 2–4; inflorescences solitary flowers, pedicels present or absent, or if flowers 2 per node (E. chilensis) then pedicels absent; plants glabrous; stems with longitudinal air spaces.||Elatine|