Description from Flora of China
Herbs perennial or biennial, rarely subshrubs, rhizomatous. Stem developed or absent, sometimes with creeping branches. Leaves simple, alternate or basal, margin entire, dentate, or dissected; stipules small or large, leaflike, free or ± adnate to petioles. Flowers bisexual, zygomorphic, solitary, often dimorphic (cleistogamous flowers later than chasmogamous ones); pedicels axillary, 2-bracteolate. Sepals slightly equal, usually basally auriculate. Petals unequal, anterior petal largest and basally spurred. Filaments free, very short; anthers free or mostly connivent into a sheath around ovary, 2 anterior ones with spurlike or wartlike and nectariferous appendages at base, these extending into anterior spur, connectives produced apically into conspicuous, membranous appendages. Ovary 3-carpelled, with many ovuled parietal placentae; styles nearly erect or usually ± curved downward, ± thickened or sometimes gradually tapering toward apex, entire or variously appendaged; style apex and stigma variously shaped. Capsule loculicidally and elastically 3-valved, valves carinate and abaxially thickened. Seeds globose-ovoid, arillate or not, usually smooth; endosperm abundant; embryo straight; cotyledons rather thick, plano-convex.
The identity of Viola curvicalcarata W. Becker & H. Boissieu (Bull. Herb. Boissier, sér. 2, 8: 740. 1908), described from Shaanxi, cannot be ascertained in this treatment because we have not seen any specimens of it.
About 550 species: cosmopolitan, chiefly in temperate regions of the N hemisphere; 96 species (35 endemic, three introduced) in China.