Elatinaceae Dum.
Including Isomeraceae Dulac
Habit and leaf form. (Sub-) shrubs, or herbs. Plants non-succulent. Annual, or perennial. Hydrophytic and helophytic (mostly tolerant of changing water levels); rooted. Leaves submerged and emergent. Leaves opposite (and decussate), or whorled (rarely); petiolate to sessile; simple; epulvinate. Lamina entire; linear to ovate, or obovate; pinnately veined; attenuate at the base. Leaves stipulate. Stipules interpetiolar. Lamina margins entire, or crenate, or serrate. Leaves without a persistent basal meristem.
Leaf anatomy. Mucilaginous epidermis present, or absent.
Lamina with secretory cavities, or without secretory cavities. Minor leaf veins without phloem transfer cells (Elatine).
Stem anatomy. Secondary thickening absent (?), or developing from a conventional cambial ring. Xylem with tracheids; with vessels. Vessel end-walls simple.
Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in inflorescences; when solitary, axillary; when aggregated, in cymes. The terminal inflorescence unit cymose. Inflorescences axillary. Flowers small; regular; 25(6) merous; cyclic; tetracyclic, or pentacyclic. Free hypanthium absent.
Perianth with distinct calyx and corolla; 410(12); 2 whorled; isomerous. Calyx 25(6); 1 whorled; polysepalous, or gamosepalous; regular; imbricate. Corolla 25(6) (the same number as K); 1 whorled; polypetalous; imbricate; regular; persistent.
Androecium 25(6), or 410(12) (i.e. the same number as or twice C). Androecial members free of the perianth; all equal; free of one another; 2 whorled, or 1 whorled (the inner whorl sometimes aborted). Androecium exclusively of fertile stamens. Stamens 25(6), or 410(12); isomerous with the perianth, or diplostemonous; when 1-whorled oppositisepalous. Anthers dorsifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral. Anther wall initially with more than one middle layer (2); of the basic type. Tapetum glandular. Pollen grains aperturate; 3 aperturate; colporate; 2-celled, or 3-celled.
Gynoecium 25(6) carpelled. Carpels isomerous with the perianth. The pistil 25(6) celled. Gynoecium syncarpous; synovarious; superior. Ovary plurilocular; 25(6) locular (but the septa sometimes not reaching the ovary apex). The odd carpel (when G3) anterior. Gynoecium stylate. Styles 25(6) (same number as locules); free; apical. Stigmas capitate. Placentation axile. Ovules 1550 per locule (i.e. many); horizontal to ascending; with lateral or superior raphe; non-arillate; anatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids pear-shaped (?), or hooked (Bergia). Endosperm formation nuclear. Embryogeny solanad.
Fruit non-fleshy; dehiscent; a capsule. Capsules valvular (septifragal). Seeds non-endospermic. Cotyledons 2 (relatively short). Embryo straight to curved, or bent. Micropyle zigzag (sometimes), or not zigzag.
Seedling. Germination phanerocotylar.
Physiology, biochemistry. Alkaloids absent (one species). Iridoids not detected. Proanthocyanidins present. Ellagic acid at least sometimes present. Saponins/sapogenins absent. Aluminium accumulation not found.
Geography, cytology. Temperate to tropical. Widespread. X = 6, 9.
Taxonomy. Subclass Dicotyledonae; Crassinucelli (probably, despite nuclear endosperm). Dahlgrens Superorder Theiflorae (?); Theales (?). Cronquists Subclass Dilleniidae; Theales. APG (1998) family of uncertain position at the highest group level. Species 40. Genera 2; Bergia, Elatine.
Illustrations. Technical details (Bergia, Elatine). Technical details (Bergia).
Cite this publication as: ‘L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000. http://biodiversity.uno.edu/delta/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991) should also be cited (see References).