Taxonomy Marcussen T. et al. 2022

Viola L., Sp. Pl. 2: 933 (1753).

Type (Brainerd 1913 (1) , page: 546): Viola odorata L.

Description.—Annual or perennial acaulescent or caulescent herbs, shrubs or very rarely treelets. Axes morphologically differentiated or not. Stipules free or adnate, small or foliaceous, margin entire, laciniate, dentate, or fimbriate. Lamina linear to reniform, more or less petiolate, margin entire, crenulate, serrate, pinnate, or pedate. Flowers axillary an solitary, rarely in cymes. Peduncle non-articulated, lacking an abscission zone at the level of the bracteoles. Corolla white to yellow, orange or violet or multicoloured with or without yellow throat, strongly zygomorphic. Calycine appendages present. Bottom petal slightly to much shorter than others and weakly differentiated, rarely larger than others. Spur scarcely exserted to very long, rarely absent. Filaments free, two lowest stamens calcarate, dorsal connective appendage large, oblong-ovate, entire. Style filiform, clavate, or capitate, variously crested or not, bearded or not, often rostellate at tip. Capsule thick-walled. Seeds few to many per carpel, obovoid to globose, often arillate. Cleistogamous flowers often produced. Base chromosome numbers x = 6, 7.

Diagnostic characters.—Flowers axillary and solitary AND peduncle non-articulated AND plant herbaceous AND temperate distribution AND bottom petal slightly to much shorter than others and weakly differentiated.

Ploidy and accepted chromosome counts.—2x, 4x, 6x, 8x, 10x, 12x, 14x, 16x, 18x, 20x, >20x. 2n = 4, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 34, 36, 40, 44, c. 44, 46, 48, 50, 52, 54, 58, 60, c. 64, 72, 76, 80, c. 80, 82, c. 96, 102, c. 120, 128.

Age.—Crown node age 30.9 (29.8–31.3) Ma [2].

Included species.—664.

Distribution.—Temperate regions and montane areas in the tropics worldwide; all continents except Antarctica

Discussion.—The two main lineages of Viola are here treated as subgenera, Neoandinium and Viola. The two subgenera differ rather consistently in aspects of growth form, leaf shape, degree of emargination of the bottom petal, shape of the anther appendages, style shape, and also in base chromosome number for the diploids investigated so far. Reiche [3, 4, 5] was the first to notice the fundamental distinction between these two sublineages of the genus. He recognised three sections, the first corresponding to subg. Viola (as sect. Sparsifoliae), the second to subg. Neoandinium (as sect. Rosulatae), and a third small section with four deviant taxa from both subgenera (sect. Confertae) [6]. Becker [7], however, treated subg. Neoandinium as one of 14 sections of the genus (as sect. Andinium).

Subdivision: 2 subgenus

Subgenus Neoandinium

Subgenus Viola 

1. Brainerd, E. Viola [Tourn.] L. In An Illustrated Flora of the Northern United States, Canada and the British Possessions: From Newfoundland to the Parallel of the Southern Boundary of Virginia, and from the Atlantic Ocean Westward to the 102d Meridian; Britton, N.L., Brown, A., Eds.; C. Scribner’s Sons: New York, NY, USA, 1913; Volume 2, pp. 545–563.

2. Marcussen, T.; Heier, L.; Brysting, A.K.; Oxelman, B.; Jakobsen, K.S. From gene trees to a dated allopolyploid network: Insights from the angiosperm genus Viola (Violaceae). Syst. Biol. 2015, 64, 84–101. [CrossRef]

3. Reiche, K.F.; Taubert, P. Violaceae. In Die Natürlichen Pflanzenfamilien, 3 (6); Engler, A., Prantl, K., Eds.; Verlag von Wilhelm Engelmann: Leipzig, Germany, 1895; pp. 322–336.

4. Reiche, K.F. Violae chilenses Ein Beitrag zur Systematik der Gattung Viola. Bot. Jahrb. 1893, 16, 405–452.

5. Reiche, K.F. Viola. In Flora de Chile; Imprenta Cervantes: Santiago, Chile, 1896; Volume 1, pp. 137–162.

6. Reiche, K.F.; Taubert, P. Violaceae. In Die Natürlichen Pflanzenfamilien, 3 (6); Engler, A., Prantl, K., Eds.; Verlag von Wilhelm Engelmann: Leipzig, Germany, 1895; pp. 322–336.

7. Becker, W. Viola L. In Die Natürlichen Pflanzenfamilien 21. Parietales und Opuntiales; Engler, A., Ed.; Wilhelm Engelmann: Leipzig, Germany, 1925; Volume 21, pp. 363–376.