A Revised Phylogenetic Classification for Viola (Violaceae)

Abstract

The genus Viola (Violaceae) is among the 40–50 largest genera among angiosperms, yet its taxonomy has not been revised for nearly a century. In the most recent revision, by Wilhelm Becker in 1925, the then-known 400 species were distributed among 14 sections and numerous unranked groups. Here, we provide an updated, comprehensive classification of the genus, based on data from phylogeny, morphology, chromosome counts, and ploidy, and based on modern principles of monophyly. The revision is presented as an annotated global checklist of accepted species of Viola, an updated multigene phylogenetic network and an ITS phylogeny with denser taxon sampling, a brief summary of the taxonomic changes from Becker’s classification and their justification, a morphological binary key to the accepted subgenera, sections and subsections, and an account of each infrageneric subdivision with justifications for delimitation and rank including a description, a list of apomorphies, molecular phylogenies where possible or relevant, a distribution map, and a list of included species. We distribute the 664 species accepted by us into 2 subgenera, 31 sections, and 20 subsections. We erect one new subgenus of Viola (subg. Neoandinium, a replacement name for the illegitimate subg. Andinium), six new sections (sect. Abyssinium, sect. Himalayum, sect. Melvio, sect. Nematocaulon, sect. Spathulidium, sect. Xanthidium), and seven new subsections (subsect. Australasiaticae, subsect. Bulbosae, subsect. Clausenianae, subsect. Cleistogamae, subsect. Dispares, subsect. Formosanae, subsect. Pseudorupestres). Evolution within the genus is discussed in light of biogeography, the fossil record, morphology, and particular traits. Viola is among very few temperate and widespread genera that originated in South America. The biggest identified knowledge gaps for Viola concern the South American taxa, for which basic knowledge from phylogeny, chromosome counts, and fossil data is virtually absent. Viola has also never been subject to comprehensive anatomical study. Studies into seed anatomy and morphology are required to understand the fossil record of the genus.

Genetic Variation versus Morphological Variability in European Peatland Violets (Viola epipsila—V. palustris Group)

“…658 recognized species; it consists of two sub-genera, 31 sections, and 20 subsections. It is distributed mainly in the temperate zones of both hemispheres and it occupies a high diversity of habitats and elevations [ 1 ]. The taxonomy of the genus is complicated due to interspecific hybridization commonly occurring between closely related species of the same section, especially in disturbed or transitional habitats, and polyploidization, which plays a key role in its evolution.…”

“…The taxonomy of the genus is complicated due to interspecific hybridization commonly occurring between closely related species of the same section, especially in disturbed or transitional habitats, and polyploidization, which plays a key role in its evolution. Both processes have enhanced the population genetic variation, leading to intraspecific variability and speciation [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ].…”

“…Nyl. ), and putative introgressive forms ([ 1 ] and references therein, [ 8 , 9 , 10 , 17 , 22 ]). These taxa belong to the subsect.…”

“…Stolonosae Kupffer of the sect. Plagiostigma Godr., the oldest (crown node of 16.6 Ma) and the most species-rich (139) of all allopolyploid Viola sections [ 1 ]. The subsect.…”

Second Eastern United States Record of <i>Viola epipsila</i> Ledeb. subsp. <i>repens</i> W.Becker (Violaceae)

“…subsp. repens W.Becker belongs, is the sixth largest infrageneric group in Viola with 41 species (Marcussen et al 2022). Members of Subsection Stolonosae, often colloquially known as the "acaulescent white" violets, are distributed over the northern hemisphere and differ from other acaulescent violets in their slender rhizome, commonly stoloniferous habit, undivided leaf blades, membranous glandular-lacerate commonly non-adnate stipules, white or pale violet flowers with short thick saccate spur, style with margined and flattened apex, and base chromosome number of x = 24 (ancestrally allotetraploid, Marcussen et al 2012).…”