There are great number of violet species, about 500, and very many cultivars. Not all are in cultivation, but a surprising number of them are amongst those who specialise in them.
In the general garden there are a handful of species in general use, including the sweet violet (Viola odorata) but the majority of plants are the slightly larger violas or the larger still pansies.
Violets are not restricted to violet blue colours, they are also available in white, pink, purple and even yellow. Violas and pansies have a similar colour range, but unlike violets which are generally a single colour, these are often multicoloured as well as the flowers being larger.
They usually have a much longer flowering season than violets, the latter mainly being confined to late winter and spring. Violas will flower from spring through to the autumn in some cases and pansies will flower non-stop all year round.
Violets need very little attention but violas and pansies in particular, with such a long flowering season, benefit from being clipped back to keep them neat. They will grow in any soil, but really need moist rather than dry conditions. They can be grown in light shade as well as sun.