Viola viarum Pollard. Section: Nosphinium. Subsection: Borealiamericanae. Limestone Riverbank Violet, Plains Violet. Phen: Apr-May. Hab: Moist to wet limestone gravel and bedrock riverbanks and streamsides, bluffs, bottomland prairies, and along roadsides and other disturbed areas formerly in natural habitat. Dist: Missouri River and Ozarks in central and lower Midwest, w. IL to se. SD, s. to MO, nw. LA and e. OK (specimens collected outside this region are not typical, do not inhabit the specific habitats of this species, and are suspected of being hybrids).

ID notes:Among heterophyllous taxa, this species is most similar to others with glabrous foliage in our region, namely V. edulis in the Edulis species group and V. egglestonii in the Viarum species group. It differs from V. edulis in its moderately to deeply pedately divided leaf blades with more slender lateral lobes, the lateral less than 1/2 as long as the terminal primary division, linear-lanceolate to lanceolate sepals acuminate from the base, sparsely bearded spurred petal, and finely spotted cleistogamous capsule. It is easily separated from V. egglestonii by its pedately divided leaf blades with the terminal primary division distinctly broader than other lobes, none of the lobes abruptly narrowed at base, acuminate sepals, rather prominent quadrate auricles elongating in fruit, sparsely bearded spurred petal, finely spotted cleistogamous capsule on a taller ascending to erect peduncle, and spotted seeds.

Origin/Endemic status: Native

Taxonomy Comments: Recent specialists (McKinney 1992; Gil-ad 1997) have dismissed this species but studies have confirmed its morphological and ecological distinctness. Plants with the largest leaf blades shallowly lobed are frequently collected as this but they appear to represent hybrids with V. missouriensis, which often grows in the vicinity.

Synonymy: = Il; = Viola ×viarum – K3, K4; ? Viola esculenta Elliott ex Greene – Tx; < Viola palmata L. var. palmata – FNA6

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