1. Claytonia virginica L. (Virginia spring beauty, spring beauty

C. virginica f. robusta (Somes) E.J. Palmer & Steyerm.

C. ozarkensis John M. Mill. & K.L. Chambers

Pl. 506 a, b; Map 2310

Plants perennial herbs (annual elsewhere), with a globose to ovoid, brown, tuberous rootstock (with taproots or rhizomes elsewhere), this 8–20 mm wide, usually positioned well below the substrate surface. Aerial stems 1 to several, 5–20 cm long, usually well-developed, erect to loosely ascending, sometimes sprawling, not succulent or thickened, glabrous. Leaves basal and a single opposite pair along the stems, glabrous. Basal leaves 1 or few (rarely more), 6–20 cm long, the blade relatively thick, linear to narrowly oblanceolate or narrowly elliptic (rarely broader), angled or tapered to a sharply pointed tip, long-tapered to an indistinct, short to long petiole, green to dark green, sometimes reddish-tinged. Stem leaves 4–15 cm long, sessile or with a short, indistinct petiole, the blade relatively thick, linear to narrowly oblanceolate or narrowly elliptic, occasionally more broadly elliptic, angled or tapered to a sharply pointed tip, long-tapered at the base a single pair, variously sessile to long-petiolate. Stipules absent. Inflorescences terminal, solitary racemes 4–18 cm long, short- to long-stalked (measured from above the pair of stem leaves), with 5–18 flowers, all tending to be oriented toward 1 side of the axis, only the basal 1(2) flower(s) subtended by a membranous to herbaceous bract, this 2–9 mm long, narrowly lanceolate to ovate, more or less sheathing the axis. Flowers mostly relatively long-stalked, the stalk continuing to elongate after flowering, hypogynous; cleistogamous flowers absent. Calyces 5–7 mm long, the sepals overlapping, persistent at fruiting, remaining ascending after flowering. Petals 5, 7–14 mm long, white or pinkish-tinged, usually with pink venation, withering after the flowering. Stamens 5, the anthers pink (white elsewhere). Ovary superior, the style 3-branched above the midpoint. Fruits 2.5–5.0 mm long, ellipsoid to ovoid, with longitudinal dehiscence, the valves remaining attached, the 1–6 seeds forcibly ejected. Seeds 1–3 mm long, more or less circular (often minutely notched at the base) in outline, somewhat flattened, the surface smooth, shiny, black (dull and/or pebbled elsewhere). 2n=12 to ca. 190. February–May.

Common throughout the state (eastern U.S. west to Wisconsin and Texas; Canada). Bottomland forests, mesic upland forests, banks of streams and rivers, upland prairies, sand prairies, bases and ledges of bluffs, and occasionally margins of sinkhole ponds; also pastures, cemeteries, lawns, railroads, and roadsides.

Claytonia virginica holds the distinction of having the longest recorded series of aneuploid chromosome counts (Doyle, 1981; W. H. Lewis and Semple, 1977). In the St. Louis area alone, W. H. Lewis et al. (1967) recorded plants with 2n=22–37 and suggested that broader leaves are correlated with higher chromosome numbers. Rare plants at the broadest-leaved extreme have been called f. robusta.

The rare Claytonia ozarkensis was first described in late 2006 (J. M. Miller and Chambers, 2006). It was documented from a dozen herbarium specimens in the Ozark portions of Arkansas and Missouri, as well as east-central Oklahoma. The Missouri distribution included the type specimen from Ozark County and single historical specimens from Jefferson and Stone Counties. These specimens were determined by Steyermark (1963) as C. virginica f. robusta. Recent study of the Missouri and Oklahoma specimens has determined that, in fact, Steyermark’s determinations were correct and the plants in question are all merely broad-leaved examples of C. virginica (Yatskievych et al., 2013). Additionally, detailed searches by several botanists at the type locality in Ozark County and the site in Stone county failed to disclose plants of C. ozarkensis or suitable acidic rock outcrops for it to grow on. However, at the type locality, broad-leaved individuals of C. virginica similar to the C. ozarkensis type specimen were found intermixed with narrower-leaved plants of that species. For these reasons, C. ozarkensis must be excluded from the Missouri flora for the present and treated as endemic to Arkansas. Because the type specimen of the species was misdetermined, the taxon was of necessity renamed, C. arkansana Yatsk., R. Evans & Witsell, and the name C. ozarkensis technically becomes a synonym of C. virginica.

Claytonia arkansana is superficially less similar to C. virginica than to C. caroliniana Michx., which is widespread in the eastern United States and adjacent Canada, and to C. ogilviensis McNeill, a rare endemic in northwestern Canada. It was distinguished morphologically from these taxa in the monograph of the genus (J. M. Miller and Chambers, 2006, as C. ozarkensis). Subsequently, Croft et al. (2011) provided genetic evidence to support the distinctness of the Arkansas populations. It is restricted to horizontal ledges and tops of sandstone bluffs where plants usually are rooted in relatively deeply incised rock seams. Seed dispersal in the plants is unusual in that the inflorescences become recurved back into the crevice as the fruits mature, depositing the seeds back into suitable habitat adjacent to the maternal parent (Matthew Albrecht, Missouri Botanical Garden, personal communication). When pressed and dried, specimens of C. arkansana are easily differentiated from broad-leaved plants of C. virginica because the leaves and stems become very flaccid, thin, and translucent (whereas, plants of the latter species generally remain firm and opaque). The key below, which is adapted from J. M. Miller and Chambers (2006), provides additional characters to distinguish the two. Because sandstone bluffs occur in several Missouri counties, it is possible that this unusual rare species eventually may be discovered growing in the state.