sect. Trigynobrathys
Shrubs, subshrubs or perennial to annual herbs up to 2 m tall, the shrubs evergreen (or deciduous?), glabrous or very rarely with simple hairs, without dark glands, with taproot; branching pseudo-dichotomous or dichasial/monochasial or mixed, from up to 10 nodes. Stems 4-(rarely 6-) lined and compressed (ancipitous)when young and in distal nodes of herbaceous species, sooner or later becoming terete in shrubby species, densely glandular (when young in shrubby species); cortex exfoliating in strips or persistent; bark smooth. Leaves opposite or rarely 3-whorled, decussate, sessile, free to completely perfoliate, not forming interfoliar ridge or with base sheathing, deciduous at base or persistent (in herbaceous species); lamina entire, with venation parallel to pinnate or 1-nerved or secondarily with up to 7 basal veins, open? or closed, with tertiary venation laxly to densely reticulate or absent; laminar glands punctiform or rarely united in lines or striae; marginal gland dots dense, very small; ventral resin glands absent. Inflorescence 1-flowered with branching pseudo-dichotomous (usually from uppermost node) or 2-∞-flowered with branching dichasial/monochasial from uppermost node, often with subsidiary branches from lower nodes; bracts and bracteoles foliar or reduced. Flowers stellate, homostylous. Sepals 5(4), free, persistent, erect in fruit, with margin entire; veins 1-11; laminar glands wholly linear to mostly punctiform; marginal, submarginal, and inframarginal glands absent. Petals 5(4), persistent, with apiculus terminal or subterminal to obsolete, acute to acuminate or obtuse; margin entire; marginal glands absent; laminar glands wholly linear or distally interrupted to punctiform or absent. Stamen fascicles basically 5(4?), with 1-c. 80 stamens per fascicle, fascicles free or usually all united to form continuous or interrupted narrow ring of stamens or more rarely united 2 + 2 + 1 or stamens irregularly grouped, persistent; filaments very shortly united or apparently free; anthers yellow, gland amber; pollen type VIII. Ovary with (2)3-5(6-8) parietal placentae, ∞-ovulate; styles (2)3-5(6-8), free from bases contiguous; stigmas clavate to broadly capitate. Capsule (2)3-5-valved, coriaceous to chartaceous, with valves obscurely narrowly longitudinally vittate, sometimes with 1-3 flattish vesicles. Seeds narrowly cylindric, not carinate, without apical expansion; testa linear- scalariform to ribbed-scalariform or more rarely linear-reticulate to irregularly reticulate.
BASIC CHROMOSOME NUMBERS (x). 12, 8(9); ploidy 1, 2, 4.
Open, damp (stream, river, and lake margins, marshes, bogs, damp grasslands, meadows, ditches, rice fields, dripping rocks, wet Pinus woods, Taxodium swamps, paramo) or dry (heaths, forest clearings, pastures, cultivated fields, roadside, dry or short grasslands, dry rocky places), on sand or clay; 0-2021 m (south of the Amazon), 0-4200 m (Andes (Chile) to Costa Rica), 0-3535 m (Nicaragua to Mexico), 0-2825 m (NW. America), 0-500 m (NE. America, Cuba), 0-3400 m (E. Asia, Australasia), 10-3500 m (Africa and Madagascar).
Brazil (south and east), Uruguay, Argentina (north), Chile (central), Paraguay, Bolivia, Peru, Ecuador, Galapagos Is., Colombia, Venezuela, Panama, Costa Rica, Nicaragua, Honduras, El Salvador, Guatemala, Belize, Mexico, Cuba, U.S.A. (western to northern and eastern), Canada (south-western to south-eastern); Japan, Ryukyu Is., Taiwan, Philippines Is., Korea (south), China (south-eastern and south), Bhutan, Sikkim, Nepal, India (Himachal Pradesh, Uttar Pradesh, West Bengal, Meghalaya, Assam, Nagaland, Manipur, Orissa, Madras), Sri Lanka, Burma, Thailand, Laos, Vietnam, Kampuchea, Malaya, Sumatera, Java, Flores, Borneo, Sulawesi, Irian Jaya, Papua New Guinea; Australia (including Tasmania), New Zealand (North, South and Stewart Islands); New Caledonia, the Hawaiian Islands; Nigeria (Bauchi Plateau), Sudan Republic, Ethiopia, Kenya, Uganda, Tanzania, Zaire (eastern and south-eastern), Burundi, Rwanda, Malawi, Zambia, Angola, Namibia (Caprivi, Waterberg Plateau), Botswana (south- eastern), Zimbabwe, Mozambique (central and south), Swaziland, South Africa (Transvaal, Natal, Cape Province south to Cape of Good Hope), Lesotho, Madagascar (centre and east). Introduced into the Azores, Ireland, Holland, France (Landes), Germany (Bavaria), Italy (Tuscany), Poland (Silesia), the U.S.S.R. (Georgia), and some species into the Dominican Republic, Japan, New Zealand, and the Hawaiian Islands.