6. Viola missouriensis Greene (Missouri violet)

V. sororia Willd. var. missouriensis (Greene) L.E. McKinney

Pl. 577 e, f; Map 2697

Plants perennial, to 40 cm tall, with a prostrate to ascending rhizome 4–6 mm thick. Aerial stems not produced. Leaves in a basal rosette, long-petiolate, the petiole glabrous. Stipules conspicuous, membranous to somewhat herbaceous, free from the petiole, narrowly lanceolate, the margins entire, glandular-hairy. Leaf blades 2–8 cm long, distinctly longer than wide, narrowly triangular to ovate-triangular, all unlobed, angled or tapered to a usually sharply pointed tip, truncate to shallowly cordate at the base, the margins finely to coarsely toothed, mostly in the basal 2/3 (subentire in the apical 1/3), the surfaces glabrous. Cleistogamous flowers produced. Flower stalks not or only slightly overtopping the leaves (those of the cleistogamous flowers arched or spreading). Sepals 6–8 mm long, oblong-lanceolate to broadly lanceolate, angled to a rounded or bluntly pointed tip, the margins glabrous, the basal auricles inconspicuous (0.5–1.0 mm long at flowering, not becoming noticeably enlarged at fruiting). Corollas (8–)10–18 mm long (except in cleistogamous flowers), the petals oriented more or less forward in life but curved or arched outward or backward toward their tips, longer than the sepals, bluish purple to light purple (with a greenish white throat sometimes with a dark border) often with somewhat darker veins, the lateral petals bearded on the upper surface with uniformly slender hairs (a few of these occasionally slightly thickened toward their tips)), the lower petal glabrous or nearly so, the spur conspicuous, usually well-exserted beyond the sepal auricles, stout and often somewhat hemispheric in shape. Stamens not exserted, typically not visible without dissection of the flower. Style slender, slightly expanded into a narrow, more or less scoop-shaped, hollow, truncate tip. Fruits 7–9 mm long, broadly ellipsoid to broadly ovoid, green to olive green, often mottled with dark purple, the surface glabrous. Seeds 1.5–2.2 mm long, brown. 2n=54. March–May.

Scattered to common nearly throughout the state (Ohio to South Carolina west to North Dakota and New Mexico). Bottomland forests, mesic upland forests, banks of streams and rivers, sloughs, margins of ponds, lakes, and sinkhole ponds, bottomland prairies, and marshes; also ditches, fallow fields, lawns, railroads, roadsides and disturbed areas.

The relationship of V. missouriensis with the widespread V. sororia remains controversial. Some authors have merged the two under the latter name (Gleason and Cronquist, 1991) or treated the former as a variety of V. sororia (McKiney, 1992). Although they occasionally grow together and some plants, particularly those collected at fruiting, can be difficult to determine, the two taxa tend to differ consistently in leaf morphology and habitat preference. Thus, they are retained as separate species in the present treatment. However, further intensive comparative studies are needed on the morphological and genetic variation within and between populations rangewide.

Steyermark (1963) reported the presence of rare, putative hybrids between V. missouriensis and V. sororia (including V. papilionacea), but these have been redetermined as V. sororia. In addition, rare putative hybrids between V. missouriensis and both V. pedatifida and V. viarum have been collected in the state.

Viola missouriensis reportedly hybridizes with most other stemless blue violets. Hybrids represented in Missouri consist of a few collections of apparent crosses with V. pedatifida and (possibly) V. viarum.