Manual of the New Zealand Flora/Elatineæ
Order VIII. ELATINEÆ.
Small herbs or undershrubs, usually growing in wet places. Leaves opposite, stipulate. Flowers minute, regular, hermaphrodite. Sepals and petals each 2–5, free, imbricate. Stamens equal in number to the petals or twice as many, hypogynous, free; anthers versatile. Ovary free, 2–5-celled; styles as many as the cells, free from the base; stigmas capitate; ovules many, attached to the inner angles of the cells, anatropous. Capsule septicidal, the valves falling away from the persistent axis and septa. Seeds straight or curved; albumen wanting, or nearly so; embryo terete, radicle next the hilum.
A small and unimportant order, spread over the whole world. Genera 2; species about 25.
1. ELATINE Linn.
Small prostrate glabrous annuals, growing in water or wet places. Leaves opposite or whorled. Flowers small, axillary, usually solitary. Sepals 2–4, membranous, obtuse. Petals the same number. Ovary globose. Capsule membranous, the septa remaining attached to the axis or evanescent. Seeds cylindric, straight, or curved, longitudinally ridged and transversely wrinkled.
Species about 6, found in most temperate and subtropical regions.
1. E. americana, Arn. in Edinb. Journ. Nat. Sc. i. 431, var. australiensis, Benth. Fl. Austral. i. 178.—A small prostrate smooth and glabrous green or reddish annual, forming matted patches 1–4 in. diam.; stems branched, rooting at the nodes, succulent. Leaves small, shortly petioled, 1–1 in. long, ovate or obovate or oblong, obtuse; margin usually furnished with a few distant glands; stipules minute, fugacious. Flowers minute, solitary, sessile. Sepals 3, obtuse. Petals often absent, when present 3, longer than the sepals. Styles 3. Stamens usually 3. Capsule globose-depressed, septa complete or evanescent at maturity. Seeds very minute.—Kirk, Students' Fl. 66. E. americana, Hook. f. Fl. Nov. Zel. i. 27; Handb. N.Z. Fl. 28. E. gratioloides, A. Cunn. Precur. n. 610.
North and South Islands, Stewart Island: Muddy places and margins of still waters, not uncommon.
The New Zealand plant, which is also found in Australia, differs from the typical form of the species, which is North American, in the flowers being, always trimerous, while in America they are usually dimerous.