Viola is agenus offlowering plants in the violetfamilyViolaceae. It is the largest genus in the family, containing over 680 species. Most species are found in thetemperate Northern Hemisphere; however, some are also found in widely divergent areas such asHawaii,Australasia, and theAndes.
SomeViola species areperennial plants, some areannual plants, and a few are smallshrubs. Many species, varieties andcultivars are grown in gardens for their ornamental flowers. Inhorticulture, the termpansy is normally used for those multi-colored large-flowered cultivars which are raised annually or biennially from seed and used extensively inbedding. The termsviola andviolet are normally reserved for small-flowered annuals or perennials, including the wild species.
Opened seed capsule ofViola arvensis (field pansy,Melanium), showing the seeds
Annual orperennialcaulescent oracaulescent (with or without a visibleplant stem above the ground)herbs,shrubs or very rarely treelets. In acaulescenttaxa the foliage and flowers appear to rise from the ground. The remainder have short stems with foliage and flowers produced in the axils of the leaves (axillary).[2]
Viola typically have heart-shaped or reniform (kidney-shaped), scallopedleaves, though a number have linear or palmate leaves.[2] The simple leaves of plants with either habit are arranged alternately; the acaulescent species produce basal rosettes. Plants always have leaves withstipules that are often leaf-like.
Theflowers of the vast majority of the species are stronglyzygomorphic withbilateral symmetry and solitary, but occasionally formcymes. The flowers are formed from fivepetals; four are upswept or fan-shaped with two per side, and there is one, broad, lobed lower petal pointing downward. This petal may be slightly or much shorter than the others and is weakly differentiated. The shape of the petals and placement defines many species, for example, some species have a "spur" on the end of each petal while most have a spur on the lower petal. The spur may vary from scarcelyexserted (projecting) to very long, such as inViola rostrata.[2]
Solitary flowers end long stalks with a pair ofbracteoles. The flowers have fivesepals that persist after blooming, and in some species the sepals enlarge after blooming. Thecorolla ranges from white to yellow, orange or various shades of blue andviolet or multicolored, often blue and yellow, with or without a yellow throat.[2]
The flowers have five freestamens with short free filaments that are oppressed against theovary, with a dorsal connective appendage that is large, entire and oblong to ovate. Only the lower two stamens arecalcarate (possessingnectary spurs that are inserted on the lowest petal into the spur or a pouch). Thestyles arefiliform (threadlike) orclavate (clubshaped), thickened at their tip, beingglobose torostellate (beaked). Thestigmas are head-like, narrowed or often beaked. The flowers have a superior ovary with one cell, which has threeplacentae, containing many ovules.[2]
After flowering,fruitcapsules are produced that are thick walled, with few to manyseeds percarpel, anddehisce (split open) by way of three valves.[3] On drying, the capsules may eject seeds with considerable force to distances of several meters.[4] The nutlike seeds, which are obovoid to globose, are typicallyarillate (with a specialized outgrowth) and have straightembryos, flatcotyledons, and soft fleshyendosperm that is oily.[5][2]
One characteristic of someViola is the elusive scent of their flowers; along withterpenes, a major component of the scent is aketone compound calledionone, which temporarily desensitizes thereceptors of the nose, thus preventing any further scent being detected from the flower until the nerves recover.[6]
First formally described byCarl Linnaeus in 1753[7] with 19 species, the genusViola bears hisbotanical authority, L.[8] WhenJussieu established the hierarchical system of families (1789), he placed Viola in theCisti (rock roses),[9] though by 1811 he suggested Viola be separated from these.[10] However, in 1802Batsch had already established a separate family, which he called Violariae based on Viola as thetype genus, with seven other genera.[11][12] Although Violariae continued to be used by some authors, such asBentham and Hooker in 1862 (as Violarieae),[13] most authors adopted the alternative name Violaceae, first proposed byde Lamarck andde Candolle in 1805,[14] andGingins (1823)[15] andSaint-Hilaire (1824).[16] However de Candolle also used Violarieae in his 1824Prodromus.[17]
Viola is one of about 25 genera and about 600 species in the largeeudicot familyViolaceae, divided into subfamilies and tribes. While most genera aremonotypic,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 notmonophyletic.Molecular phylogenetic studies show thatViola occurs in Clade I of the family, asViola,Schweiggeria,Noisettia andAllexis, in whichSchweiggeria andNoisettia are monotypic and form a sister group toViola.[18][19][20]
Viola is a large genus that has traditionally been treated insections.[19] One of these was that ofGingins (1823),[15] based on stigma morphology, with five sections (Nomimium,Dischidium,Chamaemelanium,Melanium,Leptidium).[21] The extensive taxonomic studies ofWilhelm Becker, culminating in his 1925 conspectus, resulted in 14 sections and many infrasectional groups. The largest and most diverse, being sectionViola, with 17 subsections. In addition to subsections,series were also described.[22] Alternatively, some authors have preferred to subdivide the genus into subgenera. Subsequent treatments were by Gershoy (1934)[23] and Clausen (1964),[24] using subsections and series. These were all based on morphological characteristics. Subsequent studies usingmolecular phylogenetic methods, such as that of Ballard et al. (1998) have shown that many of these traditional divisions are notmonophyletic, the problem being related to a high degree ofhybridization. In particular sectionNomimium was dismembered into several new sections and transferring part of it to sectionViola. Section Violas. lat. is represented by four sections,Violasensu stricto,Plagiostigmas. str.,Nosphiniumsensu lato. and theV. spathulata group. In that analysis, the S American sections appear to be thebasal groups, starting withRubellium, thenLeptidium. However, the exact phylogenetic relationships remain unresolved, as a consequence many different taxonomic nomenclatures are in use, including groupings referred to asGrex.[20] Marcussen et al. place the five S American sections,Andinium,Leptidium,Tridens,Rubellium andChilenium at the base of the phylogenetic tree, in that order. These are followed by the single Australian section,Erpetion, as sister group toChilenium, the northern hemisphere sections and finally the single African section,V. abyssinica. These sections are morphologically, chromosomally, and geographically distinct.[25][26][27]
The genus includesdog violets, a group of scentless species which are the most commonViola 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": NeitherStreptocarpus sect.Saintpaulia ("African violets",Gesneriaceae) norErythronium dens-canis ("dogtooth violets",Liliaceae) are related toViola.
With about 113 species, the South American sectionAndinium is the largest of theViola 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.[39] Species include;[40]
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.[42] With about 61 species including;
Habitat fragmentation has been shown to have minimal effect on the genetic diversity and gene flow of the North American woodland violetViola pubescens.[48] This may be partially attributed to the ability ofViola pubescens to continue to persist within a largely agricultural matrix.[49] This trend of unexpectedly high genetic diversity is also observed inViola palmensis, a Canary Island endemic known only from a 15 square kilometer range on La palma island.[50] 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 cleistogamous flowers often experience increased levels of inbreeding.[51] 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.
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 ofViola species, includingViola hederacea,Viola betonicifolia andViola banksii, first collected byJoseph Banks andDaniel Solander on theCook voyage toBotany Bay.[19]
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 calledmyrmecochory.[56] Violets whose seeds are dispersed this way have specialized structures on the exterior of the seeds calledelaiosomes. This interaction allows violet seed to germinate and establish in a protected, stable environment.[55]
Many violet seeds exhibit physiologicaldormancy and require some period of coldstratification to induce germination underex situ conditions.[57] Rates of germination are often quite poor, especially when seeds are stored for extended periods of time.[58] In North Americanhabitat 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 andV. guestphalica) are capable of living in soils severely contaminated with heavy metals.[60] Many violets form relationships witharbuscular 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 withchasmogamous flowers that have well-developed petals pollinated by insects. Many species also produce self-pollinatedcleistogamous 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]
The international registration authority for the genus is theAmerican Violet Society, where growers register new Violacultivars.[63] A coding system is used for cultivar description of ten horticultural divisions, such as Violet (Vt) and Violetta (Vtta).[64] Examples includeViola 'Little David' (Vtta)[65] andViola 'Königin Charlotte' (Vt).[66]
In this system violets (Vt) are defined as "stoloniferous perennials with small, highly fragrant, self-coloured purple, blue or white flowers in late winter and early spring".[64]
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 termpansy is normally used for those multi-colored, large-flowered cultivars which are raised annually or biennially from seed and used extensively inbedding. The termsviola andviolet are normally reserved for small-flowered annuals or perennials, including the wild species.[63][64]
The modern gardenpansy (V.× wittrockiana) is a plant of complex hybrid origin involving at least three species,V. tricolor (wild pansy or heartsease),V. altaica, andV. lutea (mountain pansy).[68] The hybrid horned pansy (V. ×williamsii) originates from hybridization involvinggarden pansy andViola cornuta.[69]
In 2005 in the United States,Viola cultivars (including pansies) were one of the top threebedding plant crops and 111 million dollars worth of flats ofViola were produced for the bedding flower market. Pansies and violas used for bedding are generally raised from seed, andF1 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.[70]
There are hundreds of perennial viola and violetta cultivars; many of these do not breed true from seed and therefore have to bepropagated from cuttings. Violettas can be distinguished from violas by the lack of ray markings on their petals.[63] The following cultivars, of mixed or uncertain parentage, have gained theRoyal Horticultural Society'sAward of Garden Merit:[71]
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 ofViola flowers. The young leaves are edible raw or cooked as a mild-tastingleaf 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 ofV. odorata adds inimitable sweetness to desserts, fruit salads, and teas while the mild pea flavor ofV. tricolor combines equally well with sweet or savory foods, like grilled meats and steamed vegetables. The heart-shaped leaves ofV. 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]
Acandied violet or crystallized violet is a flower, usually ofViola 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 forrose petals and was applied toorange flowers in the past (whenalmonds or orange peel are treated this way they are calledpralines). Candied violets are still made commercially inToulouse, France, where they are known asviolettes de Toulouse. They are used as decorating cakes or trifles or included in aromatic desserts.[81][82]
ManyViola species containantioxidants calledanthocyanins. Fourteen anthocyanins fromV. yedoensis andV. prionantha have been identified. Some anthocyanins show strong antioxidant activities.[83] Most violas tested and many other plants of the family Violaceae containcyclotides,[84][85][86] which have a diverse range ofin vitro biological activities when isolated from the plant, including uterotonic, anti-HIV, antimicrobial, and insecticidal activities.[87]Viola canescens, a species from India, exhibitedin vitro activity againstTrypanosoma cruzi.[88]
Viola has been evaluated in different clinical indications in human studies. A double blind clinical trial showed that the adjuvant use ofViola odorata syrup with short-acting β-agonists can improve thecough suppression in children withasthma.[89][90] In another study intranasal administration ofViola odorata extract oil showed to be effective in patients withinsomnia.[90] Topical use of an herbal formulation containingViola tricolor extract also showed promising effects in patients with mild-to-moderateatopic dermatitis.[91]
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]
Violets became symbolically associated with romantic love between women.[101][102] This connection originates from fragments of a poem bySappho 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 alesbian relationship,La Prisonnière byÉdouard Bourdet, used a bouquet of violets to signify lesbian love.[105][106]
Violets, and badges depicting them,[107][108]were sold in fund-raising efforts in Australia and New Zealand on and aroundViolet Day[109] in commemoration of the lost soldiers ofWorld War I.[110]
^Zhang, J.; et al. (2011). "Rapid separation and identification of anthocyanins from flowers ofViola yedoensis andV. prionantha by high-performance liquid chromatography-photodiode array detection-electrospray ionisation mass spectrometry".Phytochemical Analysis.23 (1):16–22.doi:10.1002/pca.1320.PMID21523841.
^Trabi, M.; et al. (2009). "Circular proteins fromMelicytus (Violaceae) refine the conserved protein and gene architecture of cyclotides".Organic and Biomolecular Chemistry.7 (11):2378–88.doi:10.1039/b823020j.PMID19462049.
^Dua, VK; Verma, G; Agarwal, DD; Kaiser, M; Brun, R (Apr 2011). "Antiprotozoal activities of traditional medicinal plants from the Garhwal region of North West Himalaya, India".Journal of Ethnopharmacology.136 (1):123–128.doi:10.1016/j.jep.2011.04.024.PMID21527328.
^Myers, JoAnne (2003).The A to Z of the Lesbian Liberation Movement: Still the Rage (The A to Z Guide Series, No. 73 ) (1st ed.). Lanham, Maryland:The Scarecrow Press. p. 242.ISBN978-0-8108-6811-3.
Gershoy, A (1934).Studies in North American violets. III. Chromosome numbers and species characters. Bulletin no. 367. Vermont Agricultural Experiment Station.
Elisafenko, T. V. (19 August 2015). "Features of seed germination in different ecological groups of the species of the section Violidum, subgenus Nomimium, genus Viola L. (Violaceae)".Contemporary Problems of Ecology.8 (4):523–533.doi:10.1134/S199542551504006X.S2CID16291866.
Kopper, Brian J.; Charlton, Ralph E.; Margolies, David C. (2000). "Oviposition Site Selection by the Regal Fritillary, Speyeria idalia, as Affected by Proximity of Violet Host Plants".Journal of Insect Behavior.13 (5):651–665.doi:10.1023/A:1007887809621.S2CID19315345.
Gonzáles, Paúl; Cano, Asunción (2 November 2016). "Two new species of Viola (Violaceae) named in honor of preceding Peruvian botanists".Phytotaxa.283 (1):83–90.doi:10.11646/phytotaxa.283.1.6.
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