About 500 species of annuals, perennials and subshrubs of cosmopolitan distribution. The majority of familiar species form clumps or tufted clumps with kidney to heart-shaped leaves. In the clump-formers, leaves and flowers arise directly from a cluster of rhizomes. In the tufted clump-formers leaves and flowers arise from slender stems in small tufts which in some species are numerous. Runners may also be produced. Less familiar species have ovate, lanceolate, strap-shaped or narrowly dissected leaves. Subshrubby species may be more or less bushy or produce long scandent stems that scramble through bushes. Many of the high Andean species are known as rosulate violas and mimic Sempervivum (houseleeks) or Aizoon saxifrages to an astonishing degree. Throughout the genus, however, the typical violet and pansy-shaped flowers prevail. Basically they are borne horizontally and are composed of five petals, the upper two often erect, the lateral two spreading horizontally, and the lower one broader and pointing down, with a rear nectary spur. In the true pansies the petals are broad, at least partially overlapping and arranged in a more or less vertical plane. Viola provides a primary example of cleistogamy. When the usual flowering season is over, many of the true violets produce tiny bud-like blooms, usually hidden at the base of the plant, which never open and are self-pollinating, setting seed with great regularity.
Wide habitat requirements are found in this genus from cool temperate moist woodland to hot, dry stony slopes on tropical mountains. The easy, small hardy species grow well on the rock garden, others need the sharper drainage of a scree or a moisture-retentive humus-rich rooting medium. Yet others require alpine house protection from excessive cold or winter wet. Ordinary moist but well drained soil suits most species plus partial shade, and in the species' descriptions below this is considered adequate unless otherwise stated. The Andean rosulates have a reputation for intractability in cultivation, but it is now known that at least some species can be grown to flowering size by skilled growers. During the past 25 years seed of many species has been collected (some regularly over this period) and continuous experimenting has resulted in some notable successes. A main problem is etiolation (elongation of the normally compact rosettes) in the poor light values of the lowland northern temperate zone. Cool conditions, a sparse but adequate diet and as much light as possible are essential. It is known that in any batch of seedlings some individuals will quickly etiolate, others may not. So there is some scope in selecting plants more likely to grow satisfactorily in cultivation. Propagation by seed when ripe or in spring, or by division from autumn to late winter, or after flowering. Sub-shrubby sorts can also be increased by cuttings in summer or earlier if non-blooming shoots are available. Dried seed often fails to germinate and in general should not be kept in the packet for more than six months. Seeds of species from montane to alpine habitats often need a cold (near freezing) period to trigger germination. (Spring flowering unless stated otherwise.
V = Violet, P = Pansy, R = Rosulate Viola)