Gilbert, M.R. & M. Thulin (1999) Lythraceae, Flora of Somalia 1: 194-198
Plants annual herbs, glabrous except for the calyces; stems 4-sided. Inflorescences usually axillary cymes, sometimes congested, rarely of solitary flowers; bracteoles minute. Flowers 4(-8)-merous, never heterostylous; hypanthia cylindrical or urn-shaped; sepals short, sinus horns minute or absent; petals absent or 4-8, small; stamens 1-2-times as many as the sepals, rarely fewer; ovaries usually incompletely 2-4(-5)-celled, rarely 1-celled. Capsules included within or exserted from the hypanthia, membranous, often more or less transparent-walled, dehiscing irregularly transversely; seeds very small, numerous.
Ammannia includes abour 20 species. They grow in wet areas throughout the tropics and subtropics.