15. Viola striata Aiton (pale violet, cream violet)
Pl. 576 a–c; Map
2706
Plants
perennial, with a slender to stout, prostrate to ascending rhizome 2–4 mm
thick. Stems 10–40 cm long, erect or ascending, sometimes from a spreading
base. Leaves alternate (some nodes sometimes appearing subopposite) and also
basal at flowering, mostly long-petiolate, the petiole glabrous. Stipules
relatively large and conspicuous, herbaceous, free from the petiole, the
margins with a fringe of relatively slender, deep teeth or lobes. Leaf blades
1.0–5.5 cm long, unlobed, ovate to heart-shaped, narrowly angled or tapered at
the tip, truncate to cordate at the base, the margins evenly scalloped or
bluntly toothed, the surfaces glabrous or sparsely hairy on the upper surface.
Cleistogamous flowers produced. Flower stalks not or only slightly overtopping
the leaves (those of the cleistogamous flowers erect or ascending). Sepals 7–12
mm long, lanceolate, narrowly angled to a sharply pointed tip, the margins
sometimes minutely hairy (especially on cleistogamous flowers), the basal
auricles well-developed. Corollas 8–13 mm long (except in cleistogamous
flowers), the petals oriented forward with arched or outward-curved apical
portions, longer than the sepals, white to pale cream-colored, the lower petal
usually with dark purple to brownish purple veins, the lateral petals bearded
on the upper surface with slender hairs, the lowermost petal glabrous on the
upper surface, the spur well-exserted beyond the sepal auricles, relatively
stout. Stamens not exserted, typically not visible without dissection of the
flower. Style slender, bent at the tip. Fruits 3–9 mm long, broadly ellipsoid
to ellipsoid, green, drying to tan to olive-colored, the surface glabrous.
Seeds 1.8–2.0 mm long, tan. 2n=20. April–June.
Scattered to
common in the Ozark, Ozark Border, and Mississippi Lowlands Divisions, uncommon
or absent elsewhere in the state (eastern U.S. west to Iowa and Oklahoma;
Canada). Bottomland forests, mesic upland forests, banks of streams and rivers,
fens, bases and ledges of bluffs, and margins of upland prairies, glades, and
savannas; also fencerows and roadsides.
This species is
analogous to V. bicolor, which frequents similar sites, in being
particularly abundant in somewhat disturbed sites, such as along woodland paths
and frequently flooded riparian areas. It is a decided calciphile, often
abundant in moist to wet silty loam soils. It is distinctive among stemmed
Missouri violets in its white corolla, and, even when vegetative, can be
distinguished by its lacerate stipules. Steyermark (1963) noted that it grows
well in woodland gardens.
Recent genetic
studies have shown that although V. striata has a mixed mating system
(outcrossing open flowers followed by obligately selfing cleistogamous
flowers), most of the mature fruits produced (in an Ohio population) during a
given year originated from self-pollination (Cortés-Palomec et al., 2006). This
type of reproductive system has been speculated to result in the maintenance of
high genetic variation between populations and the retention of morphological
variants within the populations in which they have developed.
Steyermark
(1963) noted the existence of a 1936 specimen in the herbarium of William
Jewell College that represents a potential Missouri record of V. canadensis
L. (tall white violet). This taxon would key imperfectly above to either V.
pubescens or V. striata. It differs from both in its petals, which
are white on the upper surface, but are strongly purplish-tinged on the undersurface.
Its stipules are similar to those of V. pubescens, and its flowers tend
to have relatively long, slender stalks and relatively small corollas.
Steyermark doubted that the specimen was correctly labeled as having been
collected in Clinton County and noted that repeated searches for the species in
the vicinity of the locality indicated on the Missouri label had not resulted
in the rediscovery of the species in the state. The specimen in question, which
appears to represent a student collection, is correctly determined, but
probably mislabeled, and the species thus continues to be excluded from the
Missouri flora. However, V. canadensis has been documented from portions
of several states surrounding Missouri and may eventually be located growing in
the state.