Viola (plant)
Viola is a genus of flowering plants in the violet family Violaceae. It is the largest genus in the family, containing over 680 species. Most species are found in the temperate Northern Hemisphere; however, some are also found in widely divergent areas such as Hawaii, Australasia, and the Andes.
Some Viola species are perennial plants, some are annual plants, and a few are small shrubs. Many species, varieties and cultivars are grown in gardens for their ornamental flowers. In horticulture, the term pansy is normally used for those multi-colored, large-flowered cultivars which are raised annually or biennially from seed and used extensively in bedding. The terms viola and violet are normally reserved for small-flowered annuals or perennials, including the wild species.
Distribution and habitat[edit]
The worldwide northern temperate distribution of the genus distinguishes it from the remaining largely tropical Violaceae genera, restricted to either Old World or New World species, while in the tropics the distribution is primarily in high mountainous areas.[2] Centres of diversity occur mainly in the northern hemisphere, in mountainous regions of eastern Asia, Melanesia, and southern Europe, but also occur in the Andes and the southern Patagonian cone of South America.[40] One of the highest species concentrations is in the former USSR.[21] Australia is home to a number of Viola species, including Viola hederacea, Viola betonicifolia and Viola banksii, first collected by Joseph Banks and Daniel Solander on the Cook voyage to Botany Bay.[19]
Ecology[edit]
Viola species 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, high brown fritillary, small pearl-bordered fritillary, pearl-bordered fritillary, regal fritillary, cardinal, and Setaceous Hebrew character. The larvae of many fritilary butterfly species use violets as an obligate host plant, although these butterflies do not always ovaposit directly onto violets.[52] While the ecology of this genera is extremely diverse, violets are mainly pollinated by members within the orders Diptera and Hymenoptera.[53] Showy flowers are produced in early spring, and clonal cleistogamous flowers are produced from late spring until the end of the growing season under favorable conditions. Cleistogamy allows plants to produce offspring year round and have more chances for establishment.[54] This system is especially important in violets, as these plants are often weak competitors for pollination due to their small size.
Many violet species exhibit two modes of seed dispersal. Once seed capsules have matured, seeds are dispelled around the plant through explosive dehiscence.[55] Viola pedata seeds have been reported being dispersed distances of up to 5 meters away from the parent plant.[55] Often, seeds are then further dispersed by ants through a process called myrmecochory.[56] Violets whose seeds are dispersed this way have specialized structures on the exterior of the seeds called elaiosomes. This interaction allows violet seed to germinate and establish in a protected, stable environment.[55]
Many violet seeds exhibit physiological dormancy and require some period of cold stratification to induce germination under ex situ conditions.[57] Rates of germination are often quite poor, especially when seeds are stored for extended periods of time.[58] In North American habitat restoration, native violets are in high demand due to their relationship with the aforementioned fritillary butterflies.[59]
Violet species occupy a diverse array of habitats, from bogs (Viola lanceolata) to dry hill prairies (V. pedata) to woodland understories (V. labradorica). While many of these species are indicators of high quality habitat, some violets are capable of thriving in a human altered landscape. Two species of zinc violet (V. calaminaria and V. guestphalica) are capable of living in soils severely contaminated with heavy metals.[60] Many violets form relationships with arbuscular mycorrhizal fungi, and in the case of the zinc violets, this allows them to tolerate such highly contaminated soils.
Flowering is often profuse, and may last for much of the spring and summer. Viola are most often spring-blooming with chasmogamous flowers that have 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.[61] In some species the showy chasmogamous flowers are infertile (e.g.,Viola sororia).[a][62]
Other uses[edit]
Culinary[edit]
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 mild-tasting leaf vegetable. The flowers and leaves of the cultivar 'Rebecca', one of the Violetta violets, have a distinct vanilla flavor with hints of wintergreen. The pungent perfume of some varieties of V. odorata adds inimitable sweetness to desserts, fruit salads, and teas while the mild pea flavor of V. tricolor combines equally well with sweet or savory foods, like grilled meats and steamed vegetables. The heart-shaped leaves of V. odorata provide a free source of greens throughout a long growing season,[80] while the petals are used for fragrant flavoring in milk puddings and ice cream or in salads and as garnishes.[81][82]
A candied violet or crystallized violet is a flower, usually of Viola odorata, preserved by a coating of egg white and crystallised sugar. Alternatively, hot syrup is poured over the fresh flower (or the flower is immersed in the syrup) and stirred until the sugar recrystallizes and has dried. This method is still used for rose petals and was applied to orange flowers in the past (when almonds or orange peel are treated this way they are called pralines). Candied violets are still made commercially in Toulouse, France, where they are known as violettes de Toulouse. They are used as decorating cakes or trifles or included in aromatic desserts.[81][82]
The French are also known for their violet syrup, most commonly made from an extract of violets. In the United States, this French violet syrup is used to make violet scones and marshmallows. Viola essence flavours the liqueurs Creme Yvette, Creme de Violette, and Parfait d'Amour. It is also used in confectionery, such as Parma Violets and C. Howard's Violet candies.
Medicinal[edit]
Many Viola species contain antioxidants called anthocyanins. Fourteen anthocyanins from V. yedoensis and V. prionantha have been identified. Some anthocyanins show strong antioxidant activities.[83] Most violas tested and many other plants of the family Violaceae contain cyclotides,[84][85][86] which have a diverse range of in vitro biological activities when isolated from the plant, including uterotonic, anti-HIV, antimicrobial, and insecticidal activities.[87] Viola canescens, a species from India, exhibited in vitro activity against Trypanosoma cruzi.[88]
Viola has been evaluated in different clinical indications in human studies. A double blind clinical trial showed that the adjuvant use of Viola odorata syrup with short-acting β-agonists can improve the cough suppression in children with asthma.[89][90] In another study intranasal administration of Viola odorata extract oil showed to be effective in patients with insomnia.[90] Topical use of an herbal formulation containing Viola tricolor extract also showed promising effects in patients with mild-to-moderate atopic dermatitis.[91]
Perfume[edit]
Viola odorata is used as a source for scents in the perfume industry. Violet is known to have a 'flirty' scent as its fragrance comes and goes. Ionone is present in the flowers, which turns off the ability for humans to smell the fragrant compound for moments at a time.[92]
Cultural associations[edit]
Birth[edit]
Violet is the traditional birth flower for February in English tradition.[93]
Geographical territories[edit]
In the United States, the common blue violet Viola sororia is the state flower of Illinois,[94] Rhode Island,[95] New Jersey[96] and Wisconsin,[97][98] In Canada, the Viola cucullata is the provincial flower of New Brunswick adopted in 1936[99] In the United Kingdom, Viola riviniana is the county flower of Lincolnshire.[100]
Lesbian and bisexual culture[edit]
Violets became symbolically associated with romantic love between women.[101][102] This connection originates from fragments of a poem by Sappho about a lost love, in which she describes her as "Close by my side you put around yourself [many wreaths] of violets and roses."[103] In another poem, Sappho describes her lost love as wearing "violet tiaras, braided rosebuds, dill and crocus twined around" her neck.[104] In 1926, one of the first plays to involve a lesbian relationship, La Prisonnière by Édouard Bourdet, used a bouquet of violets to signify lesbian love.[105][106]
Tributes[edit]
Violets, and badges depicting them,[107][108] were sold in fund-raising efforts in Australia and New Zealand on and around Violet Day[109] in commemoration of the lost soldiers of World War I.[110]