Viola missouriensis Greene. Section: Nosphinium. Subsection: Borealiamericanae. Missouri Violet. Phen: Apr-Jun (Oct-Nov); May-Jul (chasm.), Jun-Sep (cleist.). Hab: Sandy soils of bottomland forests along streams, rivers and lakeshores. Dist: W. Midwest, Great Plains and Lower Midwest, c. IN to MN, s. to w. MS, e. TX.

ID notes:Generally, this will be most similar to other Borealiamericanae with strictly or essentially glabrous foliage and narrowly ovate-triangular leaf blades in spring that broaden substantially in summer but will differ most obviously in its glabrous leaf blades with the apical portion somewhat attenuate and subentire or with remote very low teeth, and narrowly rounded and usually ciliolate sepals. In chasmogamous flower, this species can be distinguished from V. affinis additionally by its glabrous spurred petal; from V. cucullata by its short rounded auricles, lack of a conspicuously contrasting dark purple eyespot around the throat, and lateral petal beards with long narrowly linear to weakly clavate hairs; from V. langloisii by its strongly ascending to erect leaves, and short rounded auricles; and from V. pratincola and V. retusa by its short rounded auricles. In cleistogamous fruit, it can be separated from V. communis, V. cucullata, V. pratincola, and V. retusa by its heavily spotted or blotched cleistogamous capsule on a prostrate peduncle, and orange-brown unspotted or weakly marked seeds; from V. langloisii by its prostrate capsule peduncle and rounded ciliolate sepals; and from V. sororia var. 1 and V. sororia var. 2 by its ciliolate sepals and orange-brown unspotted seeds.

Origin/Endemic status: Native

Taxonomy Comments: A distinctive species when leaf, flower and fruit characters are observed. Arguments by Gil-ad (1995, 1997) and others for conspecificity between this and V. langloisii Greene ignore the several distinctions between the two. Russell (1965) argued that the present species intergrades imperceptibly into V. affinis to the east and V. langloisii to the south, but field and herbarium studies contradict this, and all taxa maintain their morphological integrity in the narrow zones of geographic overlap.

Synonymy: = F, G, Il, K1, K3, NcTx, Tx, Ballard () (in prep), Ballard, Kartesz, & Nishino (2023), Gil-ad (1998); = Viola sororia Willd. var. missouriensis (Greene) L.E.McKinney – Ar, McKinney & Russell (2002); < Viola missouriensis Greene – FNA6, K4, Tn; < Viola sororia Willd. – C

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