[2.19] Viola sect. Xanthidium

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

—Type: Viola flavicans Wedd.

Description.—Perennial herbs. Axes not morphologically differentiated. All stem rhizomatous, with leaves in loose apical rosettes. Stipules partially or largely adnate to the petiole, narrow, shallowly glandular-lacerate. Lamina lanceolate, remotely crenate, petiolate. Bracteoles narrow, shallowly glandular-lacerate. Corolla yellow with brown striation. Spur short. Style clavate, geniculate at the base, when fresh ellipsoid with broadly rounded apex (in dried condition with flattened apex), the stigmatic orifice on a small rostellum on ventral surface, bearded (Viola flavicans; Figure 9fb) or beardless (V. pallascaensis; Figure 9fc). Cleistogamous flowers apparently produced; type of cleistogamy unknown.

Diagnostic characters.—Rosulate herbs AND bracteoles glandular-lacerate AND corolla yellow AND style ellipsoid with broadly rounded apex when fresh, flattened when dry.

Distribution.—Disjunct in central-western South America (northwestern Argentina and Bolivia, central-eastern Peru) 

Included species.—2. Viola flavicans Wedd., V. pallascaensis W. Becker

Etymology.—The name Xanthidium is based on the Greek translation of the species epithet of the type species, Viola flavicans, which refers to its yellow corolla.

Discussion.—Section Xanthidium has not yet been subject to phylogenetic analysis nor has it been characterised at the chromosomal level. Becker placed neither of these species (nor their current synonyms) in any section. He identified the taxa as related, but did not include them in his genus treatment [1]. Later, Sparre ([63], page: 348) viewed this group (as the “V. flavescens-group”) as “intermediary between the sections Chilenium and Andinium”. Nicola [80] placed V. flavicans in sect. Nomimium Ging., an artificial aggregate of numerous northern hemisphere lineages and sections