[2.12.3] Viola sect. Nosphinium subsect. Langsdorffianae

Viola subsect. Langsdorffianae (W. Becker) W. Becker in Acta Horti Gothob. 2: 286. 1926 

≡ Viola [sect. Nomimium; unranked] Langsdorffianae W. Becker in Nat. Pflanzenfam., ed. 2 [Engler & Prantl], 21: 368. 1925 (excl. V. moupinensis) 

≡ Viola sect. Langsdorffianae (W. Becker) Espeut in Botanica Pacifica 9(1): 35. 2020

—Type (Shenzhen Code Art. 10.8): Viola langsdorffii Fisch. ex Ging.

=Viola sect. Arction Juz. in Schischk. & Bobrov, Fl. URSS 15: 437, 1949, nom. inval. (Shenzhen Code Art. 39.1, descr. rossica); 

Viola sect. Arction Juz. ex Zuev in Peschkova, Fl. Sibiri 10: 96. 1996, nom. inval. (Shenzhen Code Art. 40.1, without type)

Description.—Perennial, herbs. Axes morphologically differentiated into a perennial rhizome with or without a terminating apical rosette and lateral, annual floriferous stems. Stipules ovate, free, sheathing the stem, shortly glandular-fimbriate. Laminas undivided. Calycine appendages short and truncate to rounded. Petals violet, lateral bearded. Style cylindrical or slightly clavate with a weak dorsolateral swelling and ventrally oriented rostellum. Cleistogamous flowers produced, seasonal. Allo-14-ploid or allo-18-ploid (10x with additional 4x genomes from sect. Plagiostigma). Secondary base chromosome number x’ = 40.

Diagnostic characters.—Herbaceous AND aerial stems AND stipules ovate, obtuse, shortly glandular-fimbriate and sheathing the stem AND cleistogamy present.

Ploidy and accepted chromosome counts.—14x, 18x, ~22x; 2n = c. 80 (V. howellii), c. 96, 102 (V. langsdorffii), c. 120 (V. “langsdorffii” sensu Taylor & Mulligan [269]).

Age.—Crown node not known, stem node age 1.3–8.8 Ma [45].

Included species.—3. 

Viola(Langsdorffianae) sp., ined. [J. A. Calder & Roy L. Taylor 36425; or: J. A. Calder, Roy L. Taylor & L. C. Sherk 34963], 

Viola howellii A. Gray, 

Viola langsdorffii Fisch. ex Ging.

Distribution.—Western North America and northeastern Asia.

Discussion.—Subsect. Langsdorffianae is a young high-polyploid lineage that has diversified in response to climate cooling in the Pleistocene [45]. The patterns of variation within subsect. Langsdorffianae are poorly understood, but available information from phylogenetics and chromosome counts indicate that the subsection comprises three ploidy levels, each of which we tentatively refer to as species. Viola howellii (14x) occurs in the North American Pacific Northwest, V. langsdorffii (18x) occurs on both sides of Beringia from California to Japan, and a yet undescribed taxon (20x) occurs at least in the Queen Charlotte Islands of British Columbia [269].

The only phylogenetically investigated species, V. langsdorffii (18x), arose from successive allopolyploidisations involving the allodecaploid ancestor common to all Nosphinium and V. suecica (4x) of the Stolonosae and an unknown member of the Bilobatae (4x) [45]. The expected chromosome number for V. langsdorffii is [2n = 104], and the closest actual count is of 2n = 102 chromosomes in plants from Hokkaido [270]. As pointed out by Marcussen et al. [45], the numerous counts of 2n = (ca.) 96 chromosomes [44,271,272,273,274] “presumably reflect partly the great difficulty in counting many small chromosomes, and partly the wish to align counts with multiples of x = 12, the base number attributed to Langsdorffianae by early authors” [44,59]. Reports of lower chromosome counts for V. langsdorffii (2n = c. 60, c. 64, c. 72) must be rejected on the basis of being incompatible with the phylogenetic history of this species and section [45].

The lower chromosome number of Viola howellii (2n = 14x = 80) suggests that it lacks either the Stolonosae or the Bilobatae genome present in V. langsdorffii. Clausen [59] reported “tetraploid” (n = 20) and “octoploid” (n = 40) counts from Oregon, but whether these refer to the same taxon has not been confirmed; we think the counts of n = 20 may rather refer to the sympatric V. (subsect. Rostratae) aduncoides.

The counts of n = 60 and 2n = c. 120 chromosomes in plants of “V. langsdorffii” from the Queen Charlotte Islands, British Columbia [269], most likely represent the 22x level and a yet undescribed species. Presumably this taxon has acquired yet another 4x genome from sect. Plagiostigma.

Several taxa have been distinguished from Viola langsdorffii in foliage and style traits, including V. superba [275] and the acaulescent V. simulata [276] in western North America and V. kamtschadalorum in eastern Asia [61,277], but no studies have confirmed the distinctness of these taxa.