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Annual or perennial herbs (or dwarf shrubs, extra-Mal.), some stemless with rhizomes or bulbs. Leaves digitately or pinnately 3(-4)-foliolate; Stipules when present adnate with the base of the petiole. Inflorescences cymose to umbellate, 1-many-flowered. Sepals shortly connate at base, with or without apical calli. Petals coherent above the claw, contort, glabrous. Capsules loculicid by longitudinal slits, sometimes with episeptal rimae. Ovules 1 to c. 10, in 1-2 rows per cell. Seeds 1-c. 10 per cell, usually few;


Asia-Tropical: Cosmopolitan: present S. America: present the Cape: present
Cosmopolitan, at least 700 spp., mainly from S. America and the Cape, in Malesia 3 native spp.; others introduced and escaping, sometimes becoming weedy. (§ Acetosellae).


The longer filaments are frequently thickened in the basal part, as in Biophytum. The apex of the thickening may emerge as a small tooth, e.g. in O. latifolia, O. tetraphylla, and O. barrelieri. This tooth does not carry a vascular trace ().
For heterostyly see under the family.
An important study of the morphological diversity and taxonomy of the S. African species is provided by SALTER ().


Pending a revision of the S. American species, Miss LOURTEIG (Paris) advised me to accept the names of the introduced species in the current sense.
Sizes of petiole and pedicels are given only for the portion above their articulation, as the part below it is too variable. The length of a 2-lobed leaflet is measured from the base to the apex of the lobe. The length of the filaments includes that of the basal, fused, annular part.


Knuth - in Pfl. R. 1930
LINNÉ, Sp. Pl. 1753: 433