Violets hide a scent trick and a backup plan for making seeds
Sniff a sweet violet and the perfume seems to vanish almost at once. A scent compound called ionone briefly numbs the nose's receptors, so nothing more registers until they recover. The genus has other surprises, including seed capsules that fling their contents several metres and hidden flowers that never open.
Viola is the largest genus in its family, with over 680 species of annuals, perennials and a few small shrubs. Most grow across the temperate Northern Hemisphere, but others turn up in Hawaii, Australasia and the Andes, where the genus probably first arose. Hotspots of diversity lie in the mountains of eastern Asia, Melanesia and southern Europe, and one of the densest concentrations is in the former Soviet Union. A single fossil seed from Miocene lake deposits in the Polish Carpathians shows the group's age in Europe.
The flowers are lopsided, with four petals swept upward in pairs and one broad lower petal, often carrying a nectar spur that can be very long. Colours run from white and yellow through orange to blues and violets, frequently mixed. After the spring blooms, many species switch to small, closed flowers that pollinate themselves, producing clonal seed right through the growing season. Despite that self-reliance, studies of a North American woodland violet and a Canary Island species confined to 15 square kilometres found unexpectedly high genetic diversity, a sign that outcrossing still happens often.
When the dry capsule splits along three valves it can shoot seeds metres away. Flies and bees do most of the pollinating, while caterpillars of many fritillary butterflies feed only on violets. Gardeners know the big multicoloured bedding types as pansies, raised from seed each year or two.
Linnaeus described the genus in 1753 with 19 species. Botanists argued for decades over its family, name and internal sections, and DNA work since 1998 has shown many traditional groupings to be artificial; about seventeen sections are now recognised. Some so-called violets are unrelated: African violets and dogtooth violets belong to entirely different families. Australian species such as the ivy-leaved violet were first gathered by Joseph Banks and Daniel Solander at Botany Bay.
Source: Viola (plant)
