Viola (plant)

Viola, commonly called Violets, is a genus of flowering plants in the family Violaceae, with around 400-500 species distributed around the world. Most species are found in the temperate Northern Hemisphere, however viola species are also found in widely divergent areas such as Hawaii, Australasia, and the Andes in South America.

Most viola species are small perennial plants, some are annual plants, and a few are small shrubs. A number of species are grown for their ornamental flowers in borders and rock gardens; the garden pansy in particular is an extensively used spring and autumn/winter bedding and pot plant.

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Description

Viola species typically have heart-shaped leaves, though a number have palmate shaped leaves, plus other shapes. The vast majority of viola species are herbaceous, however a substantial number are acaulescent in habit without any noticeable stems, while the others have short stems with flowers produced in the axils of the leaves. The simple leaves of plants with either habit are arranged alternately; the acaulescent species produce basal rosettes. Plants always have leaves with stipules that are often leaf-like.

  The flowers of the vast majority of the species are zygomorphic with bilateral symmetry. The flowers are formed from five petals, four are upswept or fan-shaped petals with two per side, and there is one broad, lobed lower petal pointing downward. The shape of the petals and placement defines many species, for example, some viola have a "spur" on the end of each petal while most have a spur on the lower petal.

Solitary flowers are produced on long stalks with a pair of bracteoles, and have 5 sepals that remain persistent after blooming, although the sepals sometimes enlarge after blooming. The flowers have five free stamens with short filaments that are oppressed against the ovary, with only the lower two stamens having nectary spurs that are inserted on the lowest petal into the spur or pouch. The flower styles are thickened near the top and the stigmas are head-like, narrowed or often beaked. The flowers have a superior ovary that is one celled with three placentae, and contain many ovules.

After flowering, fruit capsules are produced that split open by way of three valves.^[1] Viola flowers are most often spring blooming with chasmogamous flowers with well developed petals pollinated by insects. Many species also produce self-pollinated cleistogamous flowers in summer and autumn that do not open and lack petals.^[2] The nutlike seeds have straight embryos, flat cotyledons, and soft fleshy endosperm that is oily.^[3] The seeds are often spread by ants.

Flower colours vary in the genus, ranging from violet, as their common name suggests, through various shades of blue, yellow, white, and cream, whilst some types are bicolored, often blue and yellow. Many cultivars and hybrid species have been bred in a greater spectrum of colours. Flowering is often profuse, and may last for much of the spring and summer.

One quirk of some viola is the elusive scent of their flowers; along with terpenes, a major component of the scent is a ketone compound called ionone, which temporarily desensitises the receptors in the nose; this prevents any further scent from being detected from the flower.

Uses

Culinary

When newly opened, viola flowers may be used to decorate salads or in stuffings for poultry or fish. Soufflés, cream and similar desserts can be flavoured with essence of viola flowers. The young leaves are edible raw or cooked as a somewhat bland leaf vegetable. Flowers, leaves and roots are also used for medical purposes, being rich in vitamins A and C. They also contain a type of antioxidant called an anthocyanin.

A candied violet or crystallized violet is a viola flower preserved by a coating of sugar syrup. Hot syrup is poured over the fresh flower (or the flower is immersed in the syrup), and stirred until the sugar recrystallizes, and is dried. This method is still used for rose petals, was applied for orange flowers in the past (when almonds or orange peel are treated this way they are called as pralines). Candied violets are still made commercially at Toulouse, France, where they are known as violettes de Toulouse. They are used as decorating or included in aromatic desserts.

Viola flavour the liqueurs Creme Yvette, Creme de Violette, and Parfait d'Amour. Also used in Parma Violets.

Medicinal

Viola flowers are also used to make an herbal tea that is used in Chinese herbal medicine.

Perfume

Viola odorata is used as a source for scents in the perfume industry.

By other species

Viola are used as food plants by the larvae of some Lepidoptera species, including the Giant Leopard Moth, Large Yellow Underwing, Lesser Broad-bordered Yellow Underwing and Setaceous Hebrew Character.

Selected species

  See List of Viola species for a more complete list.

• Viola arvensis - Field Pansy
• Viola banksii - (Australian) Native Violet
• Viola biflora - Yellow Wood Violet or Twoflower Violet
• Viola canina - Heath Dog Violet
• Viola hederacea - Native Violet
• Viola hirta - Hairy Violet
• Viola odorata - Sweet Violet
• Viola sororia - Common Blue Violet or Hooded Violet
• Viola pedunculata - Yellow Pansy
• Viola pubescens - Downy yellow violet
• Viola riviniana - Common Dog Violet
• Viola stagnina - Fen Violet
• Viola tricolor - Wild Pansy or Heartsease

Note: Neither Saintpaulia ("African violets") nor Erythronium dens-canis ("Dogtooth violets") are related to the true viola.

The genus includes the Dog Violets, a group of scentless species which are the most common viola in many areas, the Sweet Violet Viola odorata (named from its sweet scent), and many other species whose common name includes the word "violet". Several species are known as pansies, including the Yellow Pansy of the Pacific coasts.

The Common Blue Violet Viola sororia is the state flower of Rhode Island, Illinois, and New Jersey.

Australia is home to a number of viola, including Viola hederacea, Viola betonicifolia and Viola banksii, first collected by Joseph Banks and Daniel Solander on the Cook voyage to Botany Bay.

The modern Garden Pansy (V. × wittrockiana) is a plant of complex hybrid origin involving at least three species, V. tricolor (Wild Pansy or Heartsease), V. altaica and V. lutea (Mountain Pansy).

References

• ITIS (Accessed December 2 2002)
• The Oxford Companion to Food, by Alan Davidson, Oxford University Press. ISBN 0-19-211579-0
• Larousse Gastronomique, by Prosper Montagne (Ed.), Clarkson Potter, 2001. ISBN 0-609-60971-8