Herbs, or rarely dwarf shrubs. Leaves usually 3-foliolate, sometimes plurifoliate or pinnate, stipulate or exstipulate, alternate. Flowers regular, on axillary or radical 1- or more flowered peduncles. Sepals 5, imbricate. Petals 5, contorted. Stamens 10, free or connate at the base. Disk none. Capsule 5-celled, dehiscing loculicidally, valves adhering to the axis; seeds one or more in each cell, albuminous. About 220 species are known, of which three or four are widely distributed, and the rest from South Africa and South America. The name is from sharp, acid, in reference to the quality of many species. Dimorphic and trimorphic flowers are frequent in this genus, the apetalous ones being very fertile. The pretty Wood Sorrel, 0. Acetosella, belongs to this genus, and many of the exotic species are strikingly beautiful.

1. 0. corniculata. - This is one of the most widely dispersed plants, occurring in all save very cold countries. A small branching pubescent annual or biennial plant. Leaves all cauline, stipulate, 3-foliolate. Flowers small, yellow, two or three together. There is a handsome variety of this named rubra, with bronzed-purple foliage.

2. 0. Deppei. - A tuberous-rooted species with quadri-foliolate leaves; leaflets obcordate. Flowers large, lurid red, in umbels, produced all the Summer. Mexico.

3. 0. Valdiviensis. - A glabrous annual from 6 to 9 inches high with trifoliolate leaves and rich yellow flowers tinged with red, and borne in long-stalked umbels.

4. 0. rosea, syn. 0. floribunda. - A Brazilian perennial species with trifoliolate leaves, growing about 6 inches or more high. Leaflets ovate, emarginate. Flowers numerous, umbellate, rose or white.

5. 0. violacea. - A hardy North American plant. Leaflets 3, obcordate. Flowers few, umbellate, purplish violet, appearing in May and June.

6. 0. Bowiei. - This is one of the handsomest of the genus. A perennial about 6 inches high, slightly pubescent, with large trifoliolate leaves and rich purplish red flowers. It is a native of South Africa, and nearly hardy or quite hardy in favourable localities in this country.