[2.13.4] Viola sect. Plagiostigma subsect. Diffusae

Viola subsect. Diffusae (W. Becker) Chang in Bull. Fan Mem. Inst. Biol., ser. n., 1(3): 249, 1949 [non vidimus]

≡ Viola [unranked] (“Gruppe”) Diffusae W. Becker in Beih. Bot. Centralbl., Abt. 2, 40: 113. 1924

≡ Viola (sect. Nomimium) ser. Diffusae (W. Becker) Steenis in Bull. Jard. Bot. Buitenzorg, ser. 3, 13 (1933–1936): 260. 1934

≡ Viola sect. Diffusae (W. Becker) Ching J.Wang, Fl. Reipubl. Popularis Sin. 51: 100. 1991.

—Type (Shenzhen Code Art. 10.8): Viola diffusa Ging.

Description.—Rhizome perennial or rarely plant annual; bulbils absent. Lateral stems present: aboveground stolons, most leaves in apical rosette; rarely also aerial stems with scattered leaves. Stipules usually adnate in the lower ⅓, pale, greenish, or brown, subulate to lanceolate, acuminate, remotely long-fimbriate. Lamina ovate, ovate-oblong or elliptic, base cuneate to shallow-cordate, often decurrent, apex usually obtuse, margin crenate. Corolla usually pale pink or pale violet, with a greenish throat. Sepals linear to ovate-lanceolate; appendages short (0.3–0.8 mm), rounded or slightly denticulate. Lateral petals bearded or not; bottom petal shorter than the other petals (5–12 mm), apex acute; spur short (1–2.5 mm) and saccate. Style at apex margined and bilobate.

Diagnostic characters.—Stolons long with 1–2 leaves and a leaf rosette at apex AND stipules 1/3 adnate to petiole AND corolla mostly pale pink to pale violet, with a greenish throat AND style margined and bilobate at apex.

Ploidy and accepted chromosome counts.—4x, 8x, 12x; 2n = 24, 26, 48, 74.

Age.—Crown node age 8.5 Ma (Figure 6), stem node age 16.6 (15.4–17.0) Ma [28].

Included species.—23

Viola(Diffusae) sp. 1, ined.,

V. (Diffusae) sp. 2, ined.,

V. (Diffusae) sp. 3, ined.,

Viola amamiana Hatus.,

Viola apoensis Elmer,

Viola austroyunnanensis Y.S. Chen, sp. nov.

Viola changii J. S. Zhou & F. W. Xing,

Viola chaozhouensis Yan S. Huang, JH Ding e Q. Fan sp. nov.

V. diffusa Ging.,

V. guangzhouensis A. Q. Dong, J. S. Zhou & F. W. Xing,

Viola heyuanensis Yan S. Huang, QL Ye e Q. Fan sp. nov.

V. huizhouensis Y. S. Huang & Q. Fan,

V. jinggangshanensis Z. L. Ning & J. P. Liao,

Viola longissima Yan S. Huang & Q. Fan sp. nov.

Viola lucens W. Becker,

Viola nagasawae Makino & Hayata,

Viola nanlingensis J. S. Zhou & F. W. Xing,

Viola pendulipedunculata Yan S. Huang & Q. Fan sp. nov.

Viola pendulipes Yan S. Huang & Q. Fan sp. nov. ?

Viola pricei W. Becker,

Viola qingruii Yan S. Huang & Q. Fan sp. nov.

V. tenuis Benth.,

V. wilsonii W. Becker,

V. yunnanensis W. Becker & H. Boissieu

Distribution.—Southeastern Asia.

Discussion.—Section Plagiostigma subsect. Diffusae comprises a handful of southeast Asian species, characterisable by stolons with few internodes and a terminal leaf rosette, stipules adnate to the petiole in the lower third, and more or less lanceolate laminas with a narrow and shallow sinus. Some species have aerial stems. Most species are distinctly stiffly hairy and have pale violet or pink petals, often yellowish green at the base, with a short and narrow, pointed bottom petal and a very short spur. This subsection, although easily recognisable in most cases, is poorly understood owing to taxonomic confusion with the other stolonose subsections Australasiaticae and Stolonosae.

More than half of the species placed in subsect. Diffusae are narrow endemics native to southern China that have been discovered and described within the last 15 years [127,128,282,283,284]. These species grow on rock surfaces, often in inaccessible places, and numerous species are still undescribed in addition to the 17 cited here (Y.-S. Huang, pers. comm. [285]).