[2.2] Viola sect. Chamaemelanium

Viola sect. Chamaemelanium Ging. in Mém. Soc. Phys. Genève 2(1): 28. 1823 (1)

Type specie: Viola canadensis L.

≡Lophion Spach, Hist. Nat. Vég. [Spach] 5: 516. 1836 ≡ Lophion subg. Eulophion Nieuwl. & Kaczm. in Amer. Midl. Naturalist 3: 215. 1914, nom. inval. (Shenzhen Code Art. 22.2)—Type: Viola canadensis L.

=Viola sect. Dischidium Ging. in Mém. Soc. Phys. Genève 2(1): 28. 1823 ≡ Dischidium (Ging.) Opiz in Bercht. & Opiz, Oekon.-Techn. Fl. Böhm. [Berchtold & al.] 2(2): 7. 1839 ≡ Viola subg. Dischidium (Ging.) Peterm., Deutschl. Fl.: 65. 1846; (Ging.) Kupffer in Kusnezow et al., Fl. Caucas. Crit. 3(9): 172. 1909 (isonym); (Ging.) Juz. in Schisk. & Bobrov, Flora URSS 15: 441. 1949 (isonym) ≡ Viola [unranked] (”Gruppe”) Dischidium W. Becker in Beih. Bot. Centralbl., Abt. 2, 36: 38. 1918—Type: Viola biflora L.

≡Chrysion Spach, Hist. Nat. Vég. [Spach] 5: 509. 1836.—Type: Viola biflora L.

≡Viola [unranked] §.5. Dischidieae Boiss., Fl. Orient. 1: 452. 1867 ≡ Viola subsect. Dischidieae (Boiss.) Rouy & Foucaud, Fl. France [Rouy & Foucaud] 3: 36. 1896—Type: Viola biflora L.

=Crocion Nieuwl. & Kaczm. in Amer. Midl. Naturalist 3: 215. 1914—Type: V. pubescens Aiton

=Viola (sect. Nomimium) [unranked] (“Gruppa”) Memorabiles W. Becker in B. Fedtsch., Fl. Aziat. Ross. 8: 19. 1915 ≡ Viola sect. Memorabiles (W. Becker) Juz. in Schischk. & Bobrov, Flora URSS 15: 407. 1949—Type: Viola kusnezowiana W. Becker

=Viola “class” Orbiculares Pollard in Bot. Gaz. 26: 330. 1898, nom. inval. (Shenzhen Code Art. 33.9) ≡ Viola [unranked] Orbiculares W. Becker in Nat. Pflanzenfam., ed. 2 [Engler & Prantl], 21: 369. 1925 ≡ Viola subsect. Orbiculares (“Pollard“) Brizicky in J. Arnold Arb. 42: 326. 1961, nom inval. (Shenzhen Code Art. 41.5)—Type: Viola orbiculata Geyer ex Holz.

=Viola [unranked] D. Erectae W. Becker in Nat. Pflanzenfam., ed. 2 [Engler & Prantl], 21: 370. 1925 ≡ Viola sect. Erectae (W. Becker) Ching J.Wang, Fl. Reipubl. Popularis Sin. 51: 123. 1991.—Lectotype (designated here): Viola acutifolia (Kar. & Kir.) W. Becker

=Viola [unranked] (Untergruppe) Longicalcaratae W. Becker in Beih. Bot. Centralbl. 36(2): 38. 1918 ≡ Viola [sect. Dischidium; unranked] A. Longicalcaratae W. Becker in Nat. Pflanzenfam., ed. 2 [Engler & Prantl], 21: 370. 1925 ≡ Viola subsect. Longicalcaratae (W. Becker) W. Becker in Acta Horti Gothob. 2: 288. 1926 ≡ Viola subsect. Longicalcaratae (W. Becker) Ching J. Wang, Fl. Reipubl. Popularis Sin. 51: 119. 1991.—Lectotype (designated here): Viola wallichiana Ging.

Description.

—Perennial herbs. Axes usually morphologically differentiated into a perennial rhizome and annual aerial stems. Rhizome usually deep-buried with a fewleaved apical rosette. Lateral stems aerial, rarely stolons, sometimes reduced or absent. Stipules partially to completely herbaceous or rarely membranous, margins entire or irregularly dentate with a few teeth. Lamina cordate to lanceolate, margin crenate, lobed, or pedately divided, usually long-petiolate. Corolla yellow, white, or violet, always with a yellow throat. Spur very short, rarely longer in a few Asian species. Style clavate or capitate, variable, usually bearded at apex. Cleistogamous flowers usually produced; cleistogamy seasonal. Diploid. Base chromosome number x = 6. ITS sequence of CHAM type

Diagnostic characters.—Corolla with a yellow throat AND base chromosome number x = 6..

Ploidy and accepted chromosome counts.—2x, 4x, 6x, 8x, 12x; 2n = 12, 24, 36, 48, 72.

Age.—Crown node age 19.0 (18.0–19.3) Ma [2].

Included species.—69. 

Viola acutifolia (Kar. & Kir.) W. Becker, V. alliariifolia Nakai, V. allochroa Botsch., V. angkae Craib, V. aurea Kell., V. bakeri Greene, V. barroetana W. Schaffn. ex Hemsl., V. beckwithii Torr. & A. Gray, V. biflora L., V. brevistipulata (Franch. & Sav.) W. Becker, V. californica M. S. Baker, V. cameleo H. Boissieu, V. canadensis L., V. caucasica (Rupr.) Kolen. ex Juz., V. charlestonensis M. S. Baker & J. C. Clausen, V. coahuilensis H. E. Ballard, ined. [P. Fryxell 2692], V. confertifolia C. C. Chang, V. crassa (Makino) Makino, V. cuneata S. Watson, V. delavayi Franch., V. dimorphophylla Y. S. Chen & Q. E. Yang, V. douglasii Steud., V. eriocarpa Schwein., V. fischeri W. Becker, V. flagelliformis Hemsl., V. flettii Piper, V. franksmithii N. H. Holmgren, V. galeanaensis M. S. Baker, V. glabella Nutt., V. glaberrima (Ging. ex Chapm.) House, V. guadalupensis A. M. Powell & Wauer, V. hallii A. Gray, V. hastata Michx., V. hediniana W. Becker, V. kitamiana Nakai, V. kusnezowiana W. Becker, V. lithion N. H. Holmgren & P. K. Holmgren, V. lobata Benth., V. majchurensis Pissjauk., V. muehldorfii Kiss, V. muliensis Y. S. Chen & Q. E. Yang, V. nuttallii Pursh, V. ocellata Torr. & A. Gray, V. orbiculata Geyer ex Holz., V. orientalis (Maxim.) W. Becker, V. painteri Rose & House, V. pedunculata Torr. & A. Gray, V. pinetorum Greene, V. praemorsa Douglas, V. pubescens Aiton, V. purpurea Kellogg, V. quercetorum M. S. Baker & J. C. Clausen, V. rockiana W. Becker, V. rotundifolia Michx., V. rugulosa Greene, V. scopulorum (A. Gray) Greene, V. sempervirens Greene, V. sheltonii Torr., V. szetschwanensis W. Becker & H. Boissieu, V. tenuipes Pollard, V. tenuissima C. C. Chang, V. tomentosa M. S. Baker & J. C. Clausen, V. trinervata (Howell) Howell ex A. Gray, V. tripartita Elliott, V. uniflora L., V. urophylla Franch., V. utahensis M. S. Baker & J. C. Clausen, V. vallicola A. Nelson, V. wallichiana Ging. 

Discussion.

—Sect. Chamaemelanium is the only diploid representative of the CHAM genome; intrasectional allopolyploids are frequent but there was no hybridisation with the MELVIO lineage. The lineage is characterised karyologically by the base chromosome number x = 6 and morphologically by a plesiomorphic yellow corolla (variously coloured but always with a yellow throat in the Canadenses and Chrysanthae greges), shoots differentiated in a perennial (often deep-buried) rhizome with an apical (often few-leafed) leaf rosette and annual lateral floriferous stems, and the presence of seasonal cleistogamy. The lateral stems are usually more or less erect and aerial, in some reclining or prostrate and leafy or leafless (V. kusnezowiana in northeastern Asia, V. orbiculata, V. rotundifolia and V. sempervirens in North America), or entirely missing (V. barroetana in Mexico). Stipules in some species are semi-membranous or membranous, and are commonly entire or with one to few irregular teeth on one or both margins. Leaf lamina is usually crenate or crenulate but deeply divided in some taxa (greges Chrysanthae and Nudicaules in North America, the V. biflora group in northeastern Asia). Style shape is variable [29] but most species groups have a capitate, bearded style. Members of the V. biflora group (the former sect. Dischidium) have a bilobate style, while a few other species have style shapes resembling those found in other sections, such as sect. Viola (V. kitamiana and V. kusnezowiana in northeastern Asia) or sect. Plagiostigma (V. rotundifolia in eastern North America). Elaiosomes are highly reduced to obsolete in at least some species of the Canadenses grex. Cleistogamous flowers are missing in some taxa adapted to arid habitats (notably grex Chrysanthae and V. guadalupensis).

We recognise a broadly defined sect. Chamaemelanium that includes sect. Dischidium Ging. (i.e., the V. biflora group), grex Orbiculares Pollard (i.e., V. orbiculata, V. sempervirens and V. rotundifolia) and grex Memorabiles W. Becker (i.e., V. kusnezowiana) previously placed in sect. Nomimium by Becker [1], and V. kitamiana. The inclusion of Dischidium and Orbiculares in sect. Chamaemelanium, first suggested nearly a century ago by Clausen [29,59], is supported by morphology, chromosome counts, and by phylogeny (Figure 13) [28,60]. Viola kusnezowiana is included in sect. Chamaemelanium on basis of flower and stipule characters [61]; the somewhat emarginate lamina apex is particularly reminiscent of the V. biflora group. Viola kitamiana is included in sect. Chamaemelanium based on its corolla with a yellow throat (otherwise white) and the diploid chromosome number 2n = 12 [61].

We do not recognise infrasectional groups within sect. Chamaemelanium because its extant sublineages, at least the North American ones (Figure 13), are interconnected by allopolyploidy and therefore non-monophyletic [59,60,241,242]. Furthermore, the 7–8 diploid deep lineages do not correspond to any recognised morphological greges [1] and their interrelationships are deep and largely unresolved. For instance, both the capitate-bearded style shape and the rhizomatous habit with lateral, aerial floriferous stems, the two characters that define Becker’s grex Erectae, appear to be ancestral and plesiomorphic within sect. Chamaemelanium (Figure 13).

The initial radiation of sect. Chamaemelanium appears to have coincided with that of the CHAM + MELVIO allopolyploids in the northern hemisphere c. 19 Ma ago [28]. It has not been established whether the CHAM genomes involved in these allopolyploidisations were derived from within the extant sect. Chamaemelanium or from a lineage sister to it. It is, however, clear that the version of the CHAM genome present in the southern hemisphere sect. Chilenium and sect. Erpetion is sister to all other CHAM genomes.

The report of 2n = 20 in V. kusnezowiana [243] is at odds with the other counts in the section, all of which are based on x = 6, and in need of confirmation.

1. Marcussen, T. et al. A Revised Phylogenetic Classification for Viola (Violaceae). Plants 11, 2224 (2022)p. 42-43 

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

Photogallery