Viola (plant)

One characteristic 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 desensitizes the receptors of the nose, thus preventing any further scent being detected from the flower until the nerves recover.[5]

First formally described by Carl Linnaeus in 1753[6] with 19 species, the genus Viola bears his botanical authority, L.[7] When Jussieu established the hierarchical system of families (1789), he placed Viola in the Cisti (rock roses),[8] though by 1811 he suggested Viola be separated from these.[9] However, in 1802 Batsch had already established a separate family, which he called Violariae based on Viola as the type genus, with seven other genera.[10][11] Although Violariae continued to be used by some authors, such as Bentham and Hooker in 1862 (as Violarieae),[12] most authors adopted the alternative name Violaceae, first proposed by de Lamarck and de Candolle in 1805,[13] and Gingins (1823)[14] and Saint-Hilaire (1824).[15]However de Candolle also used Violarieae in his 1824 Prodromus.[16]

Viola is one of about 25 genera and about 600 species in the large family eudicot family Violaceae, divided into subfamilies and tribes. While most genera are monotypic, Viola is a very large genus, variously circumscribed as having between 500 and 600 species. Historically it was placed in subfamily Violoideae, tribe Violeae. But these divisions have been shown to be artificial and not monophyletic. Molecular phylogenetic studies show that Viola occurs in Clade I of the family, as Viola, Schweiggeria, Noisettia and Allexis, in which Schweiggeria and Noisettia are monotypic and form a sister group to Viola.[17][18][19]

Viola is a large genus, that has traditionally been treated in sections.[18] One of these was that of Gingins (1823),[14] based on stigma morphology, with five sections (Nomimium, Dischidium, Chamaemelanium, Melanium, Leptidium).[20] The extensive taxonomic studies of Wilhelm Becker, culminating in his 1925 conspectus, resulted in 14 sections and many infrasectional groups. The largest and most diverse, being section Viola, with 17 subsections. In addition to subsections, series were also described.[21] Alternatively, some authors have preferred to subdivide the genus into subgenera. Subsequent treatments were by Gershoy (1934)[22] and Clausen (1964),[23] using subsections and series. These were all based on morphological characteristics. Subsequent studies using molecular phylogenetic methods, such as that of Ballard et al. (1998) have shown that many of these traditional divisions are not monophyletic, the problem being related to a high degree of hybridization. In particular section Nomimium was dismembered into several new sections and transferring part of it to section Viola. Section Viola s. lat. is represented by four sections, Viola sensu stricto, Plagiostigma s. str., Nosphinium sensu lato. and the V. spathulata group. In that analysis, the S American sections appear to be the basal groups, starting with Rubellium, then Leptidium. However, the exact phylogenetic relationships remain unresolved, as a consequence many different taxonomic nomenclatures are in use, including groupings referred to as Grex.[19] Marcussen et al. place the five S American sections, Andinium, Leptidium, Tridens, Rubellium and Chilenium at the base of the phylogenetic tree, in that order. These are followed by the single Australian section, Erpetion, as sister group to Chilenium, the northern hemisphere sections and finally the single African section, V. abyssinica. These sections are morphologically, chromosomally, and geographically distinct.[24][25][26]

Seventeen sections are recognized, listed alphabetically (approximate no. species);[27][24][28]

• Sect. Andinium W.Becker (113) S America[28]
• Sect. Chamaemelanium Ging. s.lat. (61) N America, northeast Asia (includes Dischidium, Orbiculares)
  • Subsect. Chamaemelanium
  • Subsect. Nudicaules
  • Subsect. Nuttalianae
• Sect. Chilenium W.Becker (8) southern S America[29]
• Sect. Danxiaviola W. B. Liao et Q. Fan (1) China[25]
• Sect. Delphiniopsis W.Becker (3) western Eurasia: southern Spain; Balkans[30]
• Sect. Erpetion (Banks) W.Becker (11–18) eastern Australia; Tasmania
• Sect. Leptidium Ging. (19) S America[31]
• Sect. Melanium Ging. (125) western Eurasia (pansies)[18][32]
• Sect. Nosphinium W.Becker s.lat. (31–50) N, C and northern S America; Beringia; Hawaii[27]
• Sect. nov. A (V. abyssinica group) (1–3) Africa: equatorial high mountains
• Sect. nov. B (V. spathulata group) (7–9) western and central Asia: northern Iraq to Mongolia[25]
• Sect. Plagiostigma Godr. (120) northern hemisphere (includes Diffusae)[33][34][35]
  • Grex Primulifolia
• Sect. Rubellium W.Becker (3–6) S America: Chile[19]
• Sect. Sclerosium W.Becker (1–4) northeastern Africa to southwestern Asia[36]
• Sect. Tridens W.Becker (2) southern S America
• Sect. Viola  s.str. (Rostellatae nom. illeg.) (75) northern hemisphere (violets) (includes Repentes)[26]
  • Subsect. Rostratae Kupffer (W.Becker) [37]
  • Subsect. Viola
• Sect. Xylinosium W.Becker (3–4) Mediterranean region

The genus includes dog violets, a group of scentless species which are the most common Viola in many areas, sweet violet (Viola odorata) (named from its sweet scent), and many other species whose common name includes the word "violet". But not other "violets": Neither Streptocarpus sect. Saintpaulia ("African violets", Gesneriaceae) nor Erythronium dens-canis ("dogtooth violets", Liliaceae) are related to Viola.

Viola canina Section Andinium With about 113 species, the South American section Andinium is the largest of the Viola sections. It is one of the four sections distributed primarily or exclusively in South America, and the basal group of Viola. New species continue to be identified.[38] Species include;[39] Viola canina[40] Viola lilliputana[39]

Viola biflora Section Chamaemelanium Chamaemelanium was one of a number of sections originally classified on the basis of the shape of the stigma, in this case one that was facial shaped, had an absent beak and had lateral beards. But this section has subsequently been shown to be paraphyletic, requiring revision. It occurs at high altitudes (above 600 m) in both N America and northeast Asia, including Siberia and Korea, and the species are perennial, caulous and herbaceous.[41] With about 61 species including; Viola biflora – yellow wood violet, twoflower violet Viola glabella – stream violet Viola pedunculata – yellow pansy Viola praemorsa – canary violet Viola pubescens – downy yellow violet

Viola reichei Section Chilenium A small S American section with about 8 species, as sister group to Erpetion, including; Viola reichei

Section Danxiaviola

• Viola hybanthoides

Section Delphiniopsis

Viola Cazorlensis

• Viola cazorlensis
• Viola delphinantha
• Viola kosaninii

Section Erpetion[42]

Viola banksii

• Viola banksii – Australian native violet, ivy-leaved violet
• Viola hederacea – Australian native violet, ivy-leaved violet

Section Leptidium

Viola stipularis

• Viola stipularis

Section Melanium (pansies)[18][43]

Viola tricolor

• Viola arvensis – field pansy
• Viola bicolor
• Viola pedunculata – yellow pansy, Pacific coast.
• Viola bertolonii
• Viola calcarata
• Viola cheiranthifolia – Teide violet
• Viola cornuta
• Viola lutea
• Viola tricolor – wild pansy, heartsease

Section Nosphinium

Viola pedata

• Viola pedata

Section A (V. abyssinica group)

Viola abyssinica

• Viola abyssinica

Section B (V. spathulata group)

• Viola spathulata

Section Plagiostigma

Viola epipsila

• Viola epipsila

Section Rubellium

• Viola capillaris[44]
• Viola portalesia[45]
• Viola rubella

Section Sclerosium

• Viola cinerea

Section Tridens

Viola tridentata

• Viola tridentata – mountain violet

Section Viola (violets)

Viola sororia

• Viola canina – heath dog violet
• Viola hirta – hairy violet
• Viola labradorica – alpine violet
• Viola odorata – sweet violet
• Viola persicifolia – fen violet
• Viola riviniana – common dog violet
• Viola rostrata – long-spurred violet
• Viola sororia – common blue violet, hooded violet

Section Xylinosium

Viola decumbens

• Viola decumbens

One fossil seed of †Viola rimosa has been extracted from borehole samples of the Middle Miocene fresh water deposits in Nowy Sacz Basin, West Carpathians, Poland.[46] The genus is thought to have arisen in S America, most likely the Andes.[18][19]

Habitat fragmentation has been shown to have minimal effect on the genetic diversity and gene flow of the North American woodland violet Viola pubescens.[47] This may be partially attributed to the ability of Viola pubescens to continue to persist within a largely agricultural matrix.[48] This trend of unexpectedly high genetic diversity is also observed in Viola palmensis, a Canary Island endemic known only from a 15 square kilometer range on La palma island.[49] High levels of genetic diversity within these species indicate that these plants are outcrossing, even though many violet species can produce many clonal offspring throughout the year via cleistogamous flowers. Plants that produce copious amounts of clonal seeds from cleistogmaous flowers often experience increased levels of inbreeding.[50] These reportedly high rates of outcrossing and genetic diversity indicate that these violets are strong competitors for pollinators during the early spring when they are in bloom and that those pollinators can travel considerable distances between often fragmented populations.

Viola cultivar showing the large round flowers and the novel coloration that has been achieved through breeding.

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.[62][63]

Cultivars of Viola cornuta, Viola cucullata, and Viola odorata, are commonly grown from seed. Other species often grown include Viola labradorica, Viola pedata, and Viola rotundifolia.[66]

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).[67] The hybrid horned pansy (V. × williamsii) originates from hybridization involving garden pansy and Viola cornuta.[68]

In 2005 in the United States, Viola cultivars (including pansies) were one of the top three bedding plant crops and 111 million dollars worth of flats of Viola were produced for the bedding flower market. Pansies and violas used for bedding are generally raised from seed, and F1 hybrid seed strains have been developed which produce compact plants of reasonably consistent flower coloring and appearance. Bedding plants are usually discarded after one growing season.[69]

Selection of cultivated violas at the BBC Gardeners' World show, in June 2011.

There are hundreds of perennial viola and violetta cultivars; many of these do not breed true from seed and therefore have to be propagated from cuttings. Violettas can be distinguished from violas by the lack of ray markings on their petals.[62] The following cultivars, of mixed or uncertain parentage, have gained the Royal Horticultural Society's Award of Garden Merit;[70]

• 'Aspasia'[71]
• 'Clementina'[72]
• 'Huntercombe Purple'[73]
• 'Little David' (Vtta)[64]
• 'Moonlight'[74]
• 'Nellie Britton'[75]

Other popular examples include:[76]

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. 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,[77] while the petals are used for fragrant flavoring in milk puddings and ice cream or in salads and as garnishes.[78][79]

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.[78][79]

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.

Many Viola species contain antioxidants called anthocyanins. Fourteen anthocyanins from V. yedoensis and V. prionantha have been identified. Some anthocyanins show strong antioxidant activities.[80] Most violas tested and many other plants of the family Violaceae contain cyclotides,[81][82][83] which have a diverse range of in vitro biological activities when isolated from the plant, including uterotonic, anti-HIV, antimicrobial, and insecticidal activities.[84] Viola canescens, a species from India, exhibited in vitro activity against Trypanosoma cruzi.[85]

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.[86][87] In another study intranasal administration of Viola odorata extract oil showed to be effective in patients with insomnia.[87] Topical use of an herbal formulation containing Viola tricolor extract also showed promising effects in patients with mild-to-moderate atopic dermatitis.[88]

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.[89]

Violet is the traditional birth flower for February in English tradition.[90]

In the United States, the common blue violet Viola sororia is the state flower of Illinois,[91] Rhode Island,[92] New Jersey[93] and Wisconsin,[94][95] In Canada, the Viola cucullata is the provincial flower of New Brunswick adopted in 1936[96] In the United Kingdom, Viola riviniana is the county flower of Lincolnshire.[97]

Violets became symbolically associated with love between women.[98][99] 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."[100] In another poem, Sappho describes her lost love as wearing "violet tiaras, braided rosebuds, dill and crocus twined around" her neck.[101] 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.[102][103]

Violets, and badges depicting them,[104][105] were sold in fund-raising efforts in Australia and New Zealand on and around Violet Day[106] in commemoration of the lost soldiers of World War I.[107]