[2.9.3] Viola sect. Melanium subsect. Dispares

Viola subsect. Dispares Marcussen & Danihelka, subsect. nov.

Type: Viola dyris Maire

Description.—Ephemeral annual or dwarf perennial. Lamina of basal leaves entire or crenate. Calycine appendages 0.3–1 mm. Corolla with bright yellow throat. Bottom petal (spur included) 5–13 mm. Spur 1–3.5 mm. Cleistogamous flowers not produced. Pollen apertures 3 or 4. Ploidy probably 4x, 8x.

Diagnostic characters.—See Table 3 and key.

Ploidy and accepted chromosome counts.—Probably 4x, 8x; 2n = 12 (Viola poetica), 20, 22 (V. dyris), 24 (V. demetria).

Age.—Crown node c. 2.5 Ma (Figure 6), stem node age probably 11.8–12.8 Ma [28].

Included species.—3. 

Viola demetria Prolongo ex Boiss., 

Viola dyris Maire, 

Viola poetica Boiss. & Spruner

Distribution.—Disjunctly distributed in the Mediterranean area of southern Europe and northern Africa: Viola dyris in Morocco (High Atlas), V. demetria in southernmost Spain (Andalusia), and V. poetica in central Greece (Parnassos).

Etymology.—The name Dispares refers to the strikingly different general habits and life histories, and few apomorphic characters for this subsection.

Discussion.—Section Melanium subsect. Dispares is the third and last lineage nested within the basal polytomy of sect. Melanium (Figure 6). We infer that the subsection comprises three species, V. demetria, V. dyris, and V. poetica. The last species has not been investigated phylogenetically, but monophyly is strongly supported for the other two species using both ITS and chloroplast sequence data [94]. The very short calycine appendages (<1 mm) are an apomorphy for the subsection. Furthermore, all three species have stipules with the main segment resembling the lamina (crenulate in V. demetria with 0–3 narrow basal segments [i.e., palmate], entire and undivided in the other two) and small corollas (c. 5 mm in V. dyris, up to 13 mm in the other two). In both V. demetria and V. poetica the spur is intensively violet, and thicker and almost saccate in V. demetria. In other respects the three species are morphologically disparate, which probably reflects their adaptations to different extreme environments, i.e., to high-Alpine habitats in the perennials V. dyris (scree) and V. poetica (rock crevices and screes) as opposed to summer-dry habitats with a short growing season in the ephemeral annual V. demetria. The three species are also highly disjunct. Viola poetica (2n = 12) has 3-colporate pollen and is probably 4x, while V. dyris (2n = 20, 22) and V. demetria (2n = 24) both have 4-colporate pollen [157] and are probably 8x. The chromosome numbers 2n = 12 (V. poetica) and 2n = 24 (V. demetria) form a polyploid series; the former is unique and the latter extremely rare among pansies [65,66]. The divergence of V. demetria and V. dyris may have been relatively recent, only c. 2.7 Ma (Figure 2).