[2.13.1] Viola sect. Plagiostigma subsect. Australasiaticae

Viola subsect. Australasiaticae (M. Okamoto) Marcussen, comb. et stat. nov.

— Basionym: Viola ser. Australasiaticae M. Okamoto in Taxon 42(4): 784. 1993.

—Type: Viola sumatrana Miq.

Description.—Rhizome perennial; bulbils absent. Lateral stems usually present: aboveground stolons, most leaves scattered. Stipules free or adnate at base only, brown, linear-lanceolate to broadly lanceolate, long-fimbriate. Lamina triangular-ovate to reniform, base cuneate to deeply cordate, apex obtuse to acuminate, margin crenate or mucronulate. Corolla white or pale violet. Sepals linear-lanceolate to lanceolate; appendages short or absent (0–1.4 mm), rounded or slightly denticulate. Lateral petals not bearded; bottom petal shorter than the other petals (5–12 mm), acute to obtuse; spur short (1–2.5 mm) and saccate. Style at apex margined and bilobate.

Diagnostic characters.—Plants usually stoloniferous AND stolons with most leaves scattered AND sepals linear-lanceolate to lanceolate AND lateral petals glabrous AND bottom petal shorter than the others AND style margined and bilobate at apex.

Ploidy and accepted chromosome counts.—4x? 8x; 2n = 46.

Age.—Crown node age c. 12.0 Ma; stem node c. 16.3 Ma (Figure 6).

Included species.—10.

Viola annamensis Baker f., vedi link 1 and link 2

Viola austrosinensis Y. S. Chen & Q. E. Yang, iNat

Viola balansae Gagnep.,

Viola duclouxii W. Becker,

Viola hossei W. Becker, see

Viola kwangtungensis Melch.,

Viola mucronulifera Hand.-Mazz.,

Viola shiweii Xiao Chen Li & Z. W. Wang, > see Phytokey 2022

Viola sikkimensis W. Becker,

Viola sumatrana Miq.

Distribution.—Southeastern Asia and Malesia.

Discussion.—Becker [1] erected (sect. Nomimium) grex Serpentes as a catch-all taxon for stoloniferous species from subtropical Asia. This group was highly heterogeneous and the constituent species have later been redistributed among sect. Viola subsects. Rostratae and Viola, and sect. Plagiostigma subsects. Australasiaticae, Diffusae, Patellares, and Stolonosae [86,126,229,231]. Wang [76] expanded Becker’s greges, as sect. Serpentes, to include numerous Stolonosae species. Okamoto et al. [229] showed that the type species of grex Serpentes (V. serpens Blume, a synonym of V. pilosa) belongs in subsect. Viola and they therefore designated ser. Australasiaticae (type: V. sumatrana) as a replacement name for the remaining species not belonging in subsect. Viola. However, also Okamoto’s [229] Australasiaticae proved heterogeneous and including taxa from different sections and subsections. The type, V. sumatrana, was however not analysed phylogenetically before the recent study by C. Li et al. [231] which clearly identified the Australasiaticae in the strict sense as a separate lineage within sect. Plagiostigma (Figure 6). We here define subsect. Australasiaticae narrowly as comprising all known Plagiostigma species having stolons with scattered leaves, linear-lanceolate or lanceolate sepals, unbearded lateral petals, and a bilobate style.

The only chromosome counts for subsect. Australasiaticae are of 2n = 46 in V. sumatrana and V. annamensis (as V. rheophila Okamoto) and were reported without metadata by H. Okada in Okamoto et al. [229] and are therefore in need of confirmation. If proved correct, they presumably reflect the 8x level and present a unique number in the genus and a possible apomorphy for subsect. Australasiaticae. It is not known whether this chromosome number and ploidy are shared by all the members of the subsection.

Spinulose or mucronulate leaf margins (as an adaptation to guttation?) occur only in this subsection within Viola but have apparently originated twice. In Viola balansae and V. kwangtungensis the mucronules are extensions of the apex of each leaf tooth and are in the plane of the leaf. In V. mucronulifera the mucronules are adaxial extensions of the invagination between leaf teeth and are perpendicular to the plane of the leaf [231].