[2.11] Viola sect. Nematocaulon

Viola sect. Nematocaulon Marcussen, Nicola, J. M. Watson, A. R. Flores, H. E. Ballard, sect. nov.

Type: — Viola filicaulis Hook. f.

Description.—Perennial herbs. Axes not morphologically differentiated: all stems creeping, branched and remotely noded. Stipules ovate, free, remotely long-fimbriated. Lamina reniform to ovate, few-crenate, long-petiolate. Corolla small, white with violet striations, with a golden yellow throat. Spur short, yellow. Style filiform, terminated in a quadrangular stigmatic opening. Cleistogamous flowers produced; cleistogamy facultative. Chromosome number n = 36.

Diagnostic characters.—Corolla with a yellow throat AND style filiform.

Ploidy and accepted chromosome counts.—Ploidy unknown; 2n = 72.

Age.—Unknown.

Distribution.—New Zealand

Included species.—1. 

Viola filicaulis Hook. f. 

Etymology.—The name Nematocaulon is a Greek translation of the species epithet of the type species, Viola filicaulis, which refers to the creeping stems of that species.

Discussion.—Viola filicaulis is distinct from all other groups and species of violets, as noted already by Hooker [261] in the protologue. Becker [1] noted in the introduction to his treatment of Viola that V. filicaulis was sufficiently distinct to be placed in a section of its own, although he did not erect one. DNA samples of V. filicaulis have not been available for phylogenetic analysis. However, its morphological affinities are clearly with the other southern hemisphere sections of subg. Viola. In having a filiform style it is most similar to the species of sect. Tridens, sect. Erpetion, and sect. Leptidium. In the violet-striate pigmentation and shape of the corolla it approaches sect. Tridens (which, however, lacks the yellow throat) and in expressing facultative cleistogamy it is similar to sect. Chilenium and sect. Leptidium. The high chromosome number of V. filicaulis (2n = 72 [262]) also agrees with polyploidy in all of these sections. At the same time, style shape, stem not differentiated in a rhizome and lateral stems, and facultative cleistogamy effectively exclude an affinity of V. filicaulis to the morphologically superficially similar sections in the northern hemisphere (i.e., Chamaemelanium, Nosphinium, Plagiostigma, and Viola).

Viola filicaulis produces cleistogamous flowers in abundance, both seasonally (during summer) and facultatively under unfavourable conditions. These are, however, more morphologically variable and appear less specialised (petals reduced but not absent, number of fertile stamens variable) than in the sympatric V. cunninghamii which belongs in sect. Plagiostigma subsect. Bilobatae and which has a north-temperate origin [26,263].