Perennial (rarely annual) herbs, or undershrubs, terrestrial or aquatic, sometimes stoloniferous ( Gunnera). Leaves opposite, spiral, or verticillate, in the terrestrial species nearly always simple, in the aquatic ones always partly pinnately divided, pinnately nerved or (in Gunnera) palmately nerved. Stipules 0, but the leaves often flanked by small, subulate and caducous enations. Flowers mostly in spike-like inflorescences, sometimes in a compound panicle, mostly solitary or (sometimes) in clusters of up to a dozen flowers in the axil of a bract or reduced leaf, ♀ monoecious, dioecious or polygamous, perigynous, actinomorphous, mostly 4-merous, or 2-, or (not in Mal.) 3-merous. Sepals 4 or 2, rarely (not in Mal.) 3, in ♀ flowers sometimes much reduced to 0, free or little connate, mostly persistent. Petals alternisepalous, 4, 2 or 0, rarely 3 (not in Mal.), free, in ♀ flowers absent or strongly reduced, often soon caducous, mostly more or less unguiculate and cochleariform, longer than the sepals. Stamens as many as sepals and then epi- or alternisepalous, or twice as many, 8, 4 or 2, rarely (not in Mal.) 3 fertile and 3 sterile, or 1, in ♀ flowers completely reduced; filaments mostly filiform, long and very thin, rarely (not in Mal.) short and thick; anthers 2-celled, basifixed, latrorse, mostly oblong to linear, rarely ± elliptic. Disk 0. Ovary 1- or 4-, rarely 2- or (not in Mal.) 3-celled, in the ♂ flowers 0 or reduced; style alternisepalous, free, mostly short, grading into the globose or subulate stigmas which spread in fruit, the stigmatic, more-celled papillae hair-like elongating towards the end of the anthesis (except in Gunnera). Ovules as many as styles, or (in Gunnera) single, apical, pendulous, anatropous and apotropous. Fruit nut-like or (in Gunnera) a drupe, variously sculptured, indehiscent 1-seeded or breaking up into 4(-2) 1- seeded mericarps. Seed with a thin testa; embryo cylindrical, surrounded by a thick, white, oily albumen, or (in Gunnera) obcordate and in top of a very copious and oily albumen. Distribution. Genera 7, with c. 150 spp., nearly all over the world, but rather rare in the tropics.