There are about 500 species of Viola L, Violaceae, which are distributed all over the world, mainly in the north temperate zone. There are about 120 species in China, which are distributed in both north and south, and some of them are for ornamental purposes. Perennial herbs, sparse subshrubs, stemless or stemless; Leaves alternate or basal, dentate or parted; Stipules last; Flowers bisexual, solitary, axillary or on scape, pedicellated, bilaterally symmetrical. There are two kinds of flowers, those with petals in spring and those without petals in summer (closed flowers), but they can bear seeds. Sepals 5, extending at base; Petals 5, the largest in the lower part, with a spur at the base; Stamens 5, the lower part 2 has glandular appendages protruding from the spur, anthers surround the pistil, and connective top has membranous appendages; The ovary is superior, 1 room, and most ovules are born on three placentas; Capsule 3-valved; The petals are boat-shaped and the keel is thick and hard. When the thin part dries and shrinks, it bends outward to shoot the seeds.