Though the best-known genus, Viola, is herbaceous, most species are shrubs, lianas or small trees. The simple leaves are alternate or opposite, often with leafy stipules or the stipules are reduced in size. Some species have palmate or deeply dissected leaves. Many species are acaulescent. The flower are solitary in panicles. Some species have cleistogamous flowers produced after or before the production of typical flowers with petals. Flowers are bisexual or unisexual, actinomorphic but typically zygomorphic with a calyx of five sepals that are persistent after flowering. Corollae have five mostly unequal petals, and the anterior petal is larger and often spurred. Plants have five stamens with the abaxial stamen often spurred at the base. The gynoecium is a compound pistil of three united carpels with one locule. Styles are simple, with the ovary superior and containing many ovules. The fruits are capsules split by way of three seams. Seeds have endosperm.
Taxonomy
That Viola, previously included by Jussieu under Cisti, should have its own family was first proposed by Ventenat in 1799, and in 1803 placed the Viola species in a new genus, Ionidium which he described as "Famille des violettes." However, in the meantime Batsch established the Violaceae, as a suprageneric rank under the name of Violariae, and as the first formal description, bears his name as the botanical authority. Batsch included eight genera in this family. Although Violariae continued to be used by some authors, such as Don and Bentham and Hooker , most authors, such as Engler, adopted the alternative name Violaceae, proposed by de Lamarck and de Candolle in 1805, and later by Gingins and Saint-Hilaire. With the establishment of higher suprafamiliar orders, which he called "Alliances", Lindley placed his Violaceae within the Violales.
Phylogeny
Historically, Violaceae has been placed within a number of orders since Lindley's treatment, principally Violales and the equivalent Parietales, although such placement was considered unsatisfactory, but also Polygalinae and Guttiferales. Of these, that of Melchior, within the Engler and Prantl system, has been considered one of the most influential. Molecular phylogenetics resulted in the Angiosperm Phylogeny Group places it as one of a large number of families within the eudicot order Malpighiales. Violaceae, as one of 42 families, is placed in a clade of 10 families within the order. Its place within the parietal clade reflects its earlier position in Parietales, those families with parietal placentation. There it forms a sister group to Goupiaceae.
Subdivision
History
The Violaceae are a medium sized family with about 22–28 genera, and about 1,000–1,100 species. Most of the genera are monotypic or oligotypic, but the three genera Viola, Rinorea, and Hybanthus include 98% of the species with about half the species in Viola, and more than three-quarters of the remainder in the other two genera. Many attempts have been made at an intrafamilial classification, but these have largely been artificial, based on floral characteristics. Subdivisions were recognized almost immediately. Early classifications identified two major divisions, that were followed by most taxonomists;
These also had biogeographical correlation, with the latter being almost exclusively S American and African, and the former being distributed in Europe in addition to the Americas. In contrast, Bentham and Hooker divided Alsodeieae, giving three tribes;
Violeae. Strictly zygomorphic
Paypayroleae. Actinomorphic wth some zygomorphic features
Alsodeieae. Strictly actinomorphic
Melchior utilized a more complex classification with two subfamilies, tribes and subtribes to recognize the place of Leonia within the Violaceae;.
Subfamily Violoideae
* Tribe Rinoreeae
** Subtribe Rinoreinae
** Subtribe Hymenantherina
** Subtribe Isodendriinae
** Subtribe Paypayrolinae
* Tribe Violeae
** Subtribe Hybanthinae
** Subtribe Violinae
Subfamily Leonioideae
The historical subdivisions shown here are those of the system of Hekking, based largely on floral symmetry, petal aestivation and petal morphology. In this system, most genera occur in the Rinoreae and Violeae tribes. Three subfamilies have been recognized: the Violoideae, Leonioideae, and Fusispermoideae.
About 600 species, in the following genera, but mainly in Viola and Hybanthus and including all four of the lianescent genera in the family
Hybanthopsis Paula-Souza
Hybanthus Jacq.
Mayanaea Lundell
Noisettia Kunth
Orthion Standl. & Steyerm.
Schweiggeria Spreng.
Viola L.
Molecular systems
studies have revealed that many of these divisions were not monophyletic, partly due to homoplasy. These studies demonstrate four major clades within the family. The molecularly defined subdivisions are;
Clade 1: Viola, Schweiggeria, Noisettia, Allexis
Clade 2: Paypayrola, Hekkingia
Clade 3: Leonia, Gloeospermum, Amphirrhox, Orthion, Mayanaea, Hybanthus concolor, the Hybanthus havanensis Group, and the Hybanthus caledonicus Group
Clade 4: largely uresolved
In Clade 1, Schweiggeria and Noisettia are monotypic and form a sister group to Viola. In addition to the major clades, there were a number of unplaced segregates.
Etymology
The family derives its name from the nominative genus, Viola.
Distribution and habitat
The Violaceae have an overall cosmopolitan distribution, but are essentially tropical and subtropical, with the exception of the numerous Northern Hemispheretemperate species of Viola, the largest genus, which is also occurs at higher altitudes in its tropical and subtropical regions, where the shrub, tree and lianescent species are concentrated. In those regions, most representative genera are the mainly woody Rinorea and Hybanthus. While Viola, Hybanthus, and Rinorea are widely distributed in both hemispheres, the remaining genera are relatively restricted in their distribution. Some are restricted to a single continent while others have a limited area involving just a single archipelago. About 70 species are found in Brazil.
