Subshrubs [shrubs] or herbs, annual, biennial, or perennial, often succulent or fleshy. Leaves opposite, subopposite, or alternate and sometimes secund, sometimes rosulate or subrosulate, exstipulate (except Portulaca and Talinopsis, with nodal or axillary hairs regarded as stipular); blade margins mostly entire, occasionally dentate to crisped. Inflorescences axillary or terminal, cymose, racemose, paniculate, or umbellate, sometimes glomerate, spikelike, or with flowers solitary, open to congested. Flowers mostly radially symmetric, sometimes slightly irregular (in Montia); sepals 2-9; petals (1-)2-19 or sometimes absent, distinct or connate basally; stamens 1-many, opposite and sometimes basally adnate to petals; gynoecium 2-9-carpelled; ovary 1, superior (half-inferior to inferior in Portulaca), 1-locular throughout or initially plurilocular and becoming 1-locular distally (in Portulaca), placentation basal or free-central, ovules 1-many; style present, sometimes branched, or absent; stigmas 1-9. Fruits capsular. Seeds smooth or sculptured, with or without strophioles or elaiosomes. x = 4-9, 11, 13, 15, 23.
Genera 20-30, species ca. 500 (9 genera, 91 species in the flora): primarily Southern Hemisphere, poorly represented in Eurasia.
The eastern New World species of Portulacaceae seem to have a closer relationship with the African species, and the western New World species a closer one with the Australian species, than the two New World groups have with each other to each other.
The outer perianth segments, referred to herein as sepals, are held by some (e.g., T. Eckardt 1976) to be modified bracteoles, the petals then representing the true sepals. However, the traditional interpretation, adopted here and in most North American floras, still finds current support (R. C. Carolin 1987). A comparable situation prevails with respect to the cauline leaves in Claytonia and other genera, which are widely interpreted to be foliaceous bracts (R. C. Carolin 1987); here again, as is appropriate in a descriptive context, the traditional terminology is employed. In Talinopsis and Portulaca, the stipular nature of the nodal or axillary hairs also has been a matter of discussion. The question was revisited by R. Geesink (1969), who denied their stipular origin.
The relationships of the family are not a matter of dispute (A. Cronquist 1981; R. C. Carolin 1987); the same cannot be said for the relationships and delimitations of the genera, which have always been labile. They are, at present, the subject of active research, which has led to the current acceptance of Phemeranthus and Cistanthe. Changes in the generic classification are discussed in the treatments of the genera concerned.
Because of the uncertain relationships, the genera and species are listed alphabetically.
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