2. Viola L. (violet)
Plants annual or
perennial herbs, with taproots or rhizomes, respectively. Aerial stems absent
or, if present, then mostly less than 35 cm tall at flowering, erect,
ascending, or spreading with ascending tips, unbranched or more or less
dichotomously few-branched, with up to 6 nodes, glabrous or hairy. Leaves all
basal or (in species with aerial stems) also alternate, the basal leaves
long-petiolate, the stem leaves short- to more commonly long-petiolate.
Stipules various, often relatively conspicuous, entire, toothed, or dissected
into several, deep, jagged lobes. Inflorescences of solitary flowers, these
axillary in species with aerial stems, appearing basal in taxa not producing
aerial stems, the flowers mostly long-stalked, with a pair of small, herbaceous
bracts positioned variously on the jointless stalk. Calyces of 5 free sepals,
each of these with a sometimes inconspicuous saclike auricle at the base.
Corollas of 5 free petals, 4–30 mm long, white or pale cream-colored to yellow,
orange, bluish purple, or multicolored, the throat yellow or greenish white,
the lowermost petal short- to long-spurred. Stamens 5, the filaments adjacent
but free, the lowermost pair bearing nectaries inserted into the petal spur,
the anther appendages relatively large, oblong-ovate, entire, membranous,
orange. Style linear or strongly thickened toward the tip (club-shaped), often
appearing slightly curved above the midpoint, the stigma variously shaped,
often lobed or positioned obliquely. Fruits 4–15 mm long, oblong-ovoid to
oblong-ellipsoid, usually green at maturity, sometimes darker in cleistogamous
flowers, in some species dehiscing explosively. Seeds 9 to many per carpel,
narrowly ovoid to obovoid or globose, the surface usually appearing dull,
finely pebbled or minutely roughened, variously colored, usually with an aril.
About 525 species, nearly worldwide.
Viola is the largest genus in the family and
has been classified historically as comprising several sections and
subsections, some of which have a well-deserved reputation as taxonomically
difficult (especially in the so-called stemless groups that do not produce
aerial stems). Much of the controversy involves differing opinions as to
whether perceived morphological differences are representative of relatively
cryptic species or whether these differences are the result of minor
differentiation between populations that is maintained through the production
of cleistogamous flowers. Cleistogamous flowers are produced later in the
growing season by many species and are obligately self-pollinated. Their stalks
often are a different length or positioned differently, and at maturity such
flowers resemble young buds (the corollas are poorly developed and the calyces
remain closed over the stamens and ovary at maturity).
For many years,
most botanists followed the taxonomic summary of North American violets by
Russell (1965), although this relatively preliminary treatment contained
insufficient comparative taxonomic data to address difficulties encountered in
determining specimens of Viola. More recently, three researchers have
focused on the taxonomy of the stemless blue violets of eastern temperate North
America, with the result that botanists have a choice between three somewhat
discordant treatments published over a five-year period (McKinney, 1992;
Ballard, 1994; Gil-Ad, 1997; and other papers by these authors). Ultimately,
resolution of taxonomic controversies in some groups must await further, more
intensive studies involving a broad sampling of populations and analysis of
molecular markers. Further notes are included below in the discussions of
selected taxa. The present treatment is adapted and updated from the author’s earlier
study of the Michigan violets (Ballard, 1994).
The attractive
flowers of the stemless blue-flowered species are used in a delicious and
beautiful jelly, candied for unique confections, and eaten in salads. The
leaves also harbor significant amounts of vitamin C and are edible as a
nutritious potherb in spring. Steyermark (1963) noted that the young foliage of
most of the stemless blue violets is mucilaginous and can be eaten raw or
cooked, with a texture similar to that of okra.