[2.18.1] Viola sect. Viola subsect. Rostratae 

Viola subsect. Rostratae (Kupffer) W. Becker in Acta Horti Gothob. 2: 285. 1926 

≡ Viola [unranked] (“Gruppe”) Rostratae Kupffer in Oesterr. Bot. Z. 53: 328. 1903 

≡ Viola sect. Rostratae (Kupffer) Kupffer in Kusnezow et al., Fl. Caucas. Crit. 3(9): 193. 1909 

≡ Viola [sect. Nomimium) [unranked] Rostratae (Kupffer) Becker in Nat. Pflanzenfam., ed. 2 [Engler & Prantl], 21: 365. 1925.

—Lectotype (designated here): Viola riviniana Rchb.

≡Viola sect. Trigonocarpea Godron, Fl. Lorraine, ed. 2, 1: 88. 1857 

≡ Viola subsect. Trigonocarpea (Godr.) P. Y. Fu, Fl. Pl. Herb. Chin. Bor.-Or. 6: 82. 1977; Vl. V. Nikitin in Novosti Sist. Vyssh. Rast. 33: 178. 2001 (isonym).—Lectotype (Nikitin 1996 [301], page 189): Viola riviniana Rchb.

=Viola [unranked] Rosulantes Borbás in Hallier & Wohlfarth, Syn. Deutsch. Schweiz. Fl., ed. 3, 1: 196. 1892 

≡ Viola subsect. Rosulantes (Borbás) J. C. Clausen in Madroño 17: 196. 1964, nom. inval. (Shenzhen Code Art. 41.5)

=Lophion subg. Eucentrion Nieuwl. & Kaczm. in Amer. Midl. Naturalist 3: 216. 1914.—Type: Viola rostrata Pursh

=Lophion subg. Rhabdotion Nieuwl. & Kaczm. in Amer. Midl. Naturalist 3: 216. 1914.—Type: Viola striata Aiton

=Viola [sect. Nomimium; unranked] Umbraticolae W. Becker in Repert. Spec. Nov. Regni Veg. 19: 396. 1923.—Type (Shenzhen Code Art. 10.8): Viola umbraticola Kunth

=Viola [unranked] Repentes Kupffer in Oesterr. Bot. Z. 53: 329. 1903 ≡ Viola subsect. Repentes (Kupffer) Juz. in Schisk. & Bobrov, Fl. URSS 15: 401.—Type: Viola uliginosa Besser

≡Viola sect. Icmasion Juz. ex Tzvelev in Cvelev, Opred. Sosud. Rast. Severo-Zapadn. Rossii: 679. 2000.—Type: Viola uliginosa Besser

=Viola subsect. Grypocerae Espeut in Botanica Pacifica 9(1): 16. 2020.—Type: Viola grypoceras A. Gray

=Viola [unranked] Mirabiles Nyman Syll. Fl. Eur.: 226. 1855, nom. inval. (Shenzhen Code Art. 38.1) ≡ Viola [unranked] b2 Mirabiles Nyman ex Borbás Syn. Deutsch. Schweiz. Fl., ed. 3, 1: 195. 1890 ≡ Viola subsect. Mirabiles (Nyman ex Borbás) Juz. in Schischk. & Bobrov, Flora URSS 15: 375. 1949 ≡ Viola sect. Mirabiles (Nyman ex Borbás) Vl. V. Nikitin in Bot. Zhurn. (Moscow & Leningrad) 83(3): 130. 1998.—Type (Shenzhen Code Art. 10.8): Viola mirabilis L.

=Viola [sect. Chilenium] subsect. Coeruleae Sparre in Lilloa 17: 414. 1949.—Type: Viola huidobrii Gay

Description.—Rhizome with an apical leaf rosette and lateral aerial stems or stolons, or all stems rhizomatous, or all stems aerial. Stipules often large and foliaceous. Style bearded or not. Capsule trigonous, forcibly ejecting seeds after dehiscence. Seeds with a small elaiosome.

Diagnostic characters.—Capsules trigonous, erect at maturity, explosive; seeds with small elaiosome covering less than 1/2 of the raphe.

Ploidy and accepted chromosome counts.—4x, 8x, 12x; 2n = 20, 40, 58, 60.

Age.—Crown node c. 11 Ma [92]; stem node 11.8 (10.1–12.4) Ma [28].

Included species.—53. Viola acuminata Ledeb., Viola adunca Sm., V. aduncoides Á. Löve & D. Löve, V. anagae Gilli, V. appalachiensis L. K. Henry, V. canina L., V. caspia (Rupr.) Freyn, V. dirphya Tiniakou, V. elatior Fr., V. faurieana W. Becker, Viola fuscopurpurea S.R.Yi & Yan S.Huang sp. nov.

V. ganpinensis W. Becker, ined. [E. Bodinier 2176], V. grayi Franch. & Sav., V. grypoceras A. Gray, V. henryi H. Boissieu, V. huidobrii Gay, V. jordanii Hanry, V. kosanensis Hayata, V. kusanoana Makino, V. labradorica Schrank, V. lactea Sm., V. laricicola Marcussen, V. mariae W. Becker, V. mauritii Tepl., Viola ministipulata J. M. Dai, Yan S. Huang & Q. Fan,sp. nov., V. mirabilis L., V. obtusa (Makino) Makino, V. oligyrtia Tiniakou, V. ovato-oblonga (Miq.) Makino, V. papuana W. Becker & Pulle, V. pendulicarpa W. Becker, V. percrenulata H. E. Ballard, ined. [H. S. Gentry 7247], V. pseudomirabilis H. J. Coste, V. pumila Chaix, V. reichenbachiana Jord. ex Boreau, V. riviniana Rchb., V. rostrata Pursh, V. rupestris F. W. Schmidt, V. sacchalinensis H. Boissieu, V. serrula W. Becker, V. shinchikuensis Yamam., V. sieheana W. Becker, V. stagnina Kit. ex Schult., V. stewardiana W. Becker, V. striata Aiton, V. tanaitica Grosset, V. thibaudieri Franch. & Sav., V. uliginosa Besser, V. umbraticola Kunth, V. utchinensis Koidz., V. walteri House, V. websteri Hemsl., V. willkommii R. Roem. ex Willk..

Distribution.—North-temperate, except for Viola huidobrii in southern South America and V. papuana in New Guinea. Viola riviniana is naturalised in western North America, Australia, and New Zealand.

Discussion.—Within sect. Viola, this lineage is characterised by the explosive capsules, borne on erect peduncles at maturity (in fact a plesiomorphic trait within Viola). Subsection Rostratae is widely distributed in the temperate zone of Eurasia and North America; one species occurs in southern South America, and one in New Guinea. Becker [1] included in grex Rostratae only species with aerial floriferous stems but subsequent studies have shown that the subsection should be more inclusive.

Subsect. Rostratae has often been further subdivided based on shoot system but none of the segregates delimit monophyletic units, due to extensive allopolyploidy and presumably also parallel evolution. The vast majority of the species in subsect. Rostratae have a basal leaf rosette and lateral floriferous stems; these have traditionally been referred to as grex Rosulantes Borbás. In a few species the chasmogamous flowers are produced from the leaf rosette and the aerial stems develop after chasmogamous anthesis; these have been referred to as grex Mirabiles Nym. (i.e., V. mirabilis, V. pseudomirabilis, and V. willkommii). Other species have lateral stems that are stolon-like (e.g., V. anagae, V. appalachiensis, V. papuana, V. walteri; grex Repentes Kupffer: V. uliginosa) or absent altogether (e.g., V. ganpinensis, V. pendulicarpa, and V. shinchikuensis; grex Umbraticolae W. Becker: V. percrenulata and V. umbraticola). Finally, a fourth group of species that lack the basal rosette and instead have a sympodial growth system from annual floriferous stems has been referred to as grex Arosulatae Borbás (i.e., V. canina, V. elatior, V. lactea, V. pumila, V. stagnina). The formal greges Arosulatae, Mirabiles, and Rosulantes are superfluous as they are de facto synonyms of the higher taxon subsect. Rostratae as a result of being interconnected by allopolyploids (Figure 33, [84,92,302]). Among these, only the group formerly referred to as “Arosulatae” may merit recognition on ecological grounds. These western Eurasian species are ecological specialists to floodplains [303,304] and each possesses at least one stagnina genome. We suggest that this group be referred to informally as the V. stagnina group. Becker included here V. acuminata and V. jordanii by mistake: neither has a sympodial growth system lacking a basal rosette nor possesses a stagnina genome (Figure 33, [84,302]).

Morphologically, the southern South American Viola huidobrii (including its synonym V. brachypetala) belongs in subsect. Rostratae, based on having a rhizome with a terminal leaf rosette and lateral floriferous stems, violet corolla, long spur, and the characteristic rostellate style (Figure 9el). Viola huidobrii was previously included in sect. Chilenium [1,62] or sect. Rubellium [63]. It is the only species of sect. Viola native to the southern hemisphere. The Taiwanese endemic V. shinchikuensis (2n = 20) is (erroneously?) reported to be similar to subsect. Viola in having globose capsules borne on prostrate peduncles when mature [75,305] but it is phylogenetically placed in subsect. Rostratae [86] (Figure 2) with which it also shares numerous typical traits, e.g., bearded style, acute sepals with dentate appendages, bracteoles in the uppermost part of the peduncle, and thick non-hyaline stipules. The New Guinean endemic V. papuana has an unusual filiform style (which puzzled Becker; Figure 9eo) and isolated distribution but is a good match for subsect. Rostratae in other morphological characters, including the 4–9 mm long, upcurved spur and a pale violet corolla, and lateral stems or stolons. The reported chromosome count of 2n = 48 [74] is dubious.

Subsect. Rostratae, and sect. Viola as a whole, appears to have originated in western Eurasia. Only one clade, grex Rosulantes s.str., has dispersed into eastern Asia, North America, and South America.

A read-leaved mutant of V. riviniana, f. purpurea auct., is sometimes grown as an ornamental, often under the erroneous name V. labradorica hort. non Schrank.

Photogallery