Viola
Sp. Pl. 2: 933. 1753.
Gen. Pl. ed. 5, 402. 1754.
Herbs, annual or perennial, caulescent or acaulescent, homophyllous (heterophyllous in V. palmata, V. sagittata, and V. septemloba), hairs concentrated or scattered throughout. Stems usually deciduous and withering at end of season, 0–5(–10+), erect to ascending, decumbent, or prostrate, simple, [woody], leafy; from horizontal or vertical, thick, fleshy or subligneous, shallow or deep-seated rhizome (caudex); or from narrow or thick rhizomes; or spreading, thin stolons; or slender taproots in annual species and seedlings; in caulescent species, short, axillary branches are sometimes present on main stems. Leaves alternate on caulescent species, simple (compound in V. beckwithii, V. douglasii, V. hallii, V. sheltonii, and V. trinervata), petiolate; caulescent plants with 0–11(–22) basal leaves per caudex, acaulescent plants with 1–12(–18) leaves per rhizome, prostrate to erect; stipules adnate to petiole or not, not leaflike (sometimes leaflike in V. lobata), unlobed, shorter than leaves (except V. arvensis, V. bicolor, and V. tricolor); blade not overlapping basally (except occasionally in V. blanda and V. rotundifolia), ovate, reniform, deltate, orbiculate, lanceolate, spatulate, or linear, adaxial surface not mottled (except in V. hastata and V. hirsutula). Inflorescences axillary (rarely umbellate in V. sagittata forma umbelliflora) from distal and proximal stem nodes in caulescent species or scapose from rhizomes or stolons in acaulescent species, 1(–3)[–5]-flowered; peduncles not jointed; bracteoles present. Flowers: sepals entire, equal or subequal, margins ciliate or eciliate, auriculate, auricles prominent or not; upper 2 and lateral 2 petals showy, 5+ mm, lowest petal showy, not narrowed at middle of limb; lateral petals and sometimes others bearded proximally with variously shaped hairs; style bearded or beardless; spur gibbous or elongated; stamens connivent, but distinct, forming cone around ovary, not adherent to style, dehiscing introrsely, lower 2 filaments spurred with nectary that protrudes into petal spur; cleistogamous flowers absent or produced in summer, apetalous or petals 0 or 2(–3) and scarcely developed, stamens 2, usually adherent to style. Capsules ovoid, ellipsoid, oblong, spherical, or subglobose, glabrous, puberulent, or tomentose, sometimes muriculate. Seeds 6–75, spherical or ovoid, glabrous, often arillate with elaiosome. x = 6, 7.
Distribution
Nearly worldwide, temperate regions, also South America, Pacific Islands (Hawaii, Philippines, Taiwan).
Discussion
The taxonomy of Viola is often considered difficult partly because of hybridization; more than 100 named hybrids occur in the flora area. Hybrids among the blue-flowered, acaulescent species in eastern North America and among other species are well known (E. Brainerd 1924; N. H. Russell and M. Cooperrider 1955; G. L. Stebbins et al. 1963; T. S. Cooperrider 1986; L. E. McKinney 1992; H. E. Ballard 1993, 1994; A. Haines 2011).
Other factors contribute to phenotypic variation. The dimensions of leaves and stems often increase substantially between early spring and late summer (D. Klaber 1976). Stem, leaf, and flower size vary with environmental factors such as aspect, light, available soil moisture, and other edaphic conditions (Klaber; L. E. McKinney 1992).
The number of recognized taxa and the ranks attributed to taxa vary among authors (E. Brainerd 1921; N. H. Russell 1965; L. E. McKinney 1992; H. E. Ballard 1994; N. L. Gil-Ad 1997; D. B. Ward 2006).
An effort to deal with the difficulties encountered, specifically with subsect. Boreali-Americanae (W. Becker) Gil-Ad, was made by N. L. Gil-Ad (1997, 1998). Much of his species; we do not share his conclusions about some species, such as Viola hirsutula and V. subsinuata.
We do not present an infrageneric classification for Viola here. Some species complexes have been identified (for example, V. adunca, canadensis, nuttallii, palustris, and purpurea). W. Becker (1925) provided the first infrageneric classification, which was largely followed by G. K. Brizicky (1961b), a scheme largely based on style morphology. For the most part, this classification continues to be followed (T. Marcussen and T. Karlsson 2010); some of the names used to refer to species complexes (for example, Nuttallianae) were published without rank and have been incorrectly assumed to be subsections [for example, J. Clausen (1964); Marcussen and Karlsson]. Chen Y. S. et al. (2007) replaced sections with subgenera.
Branching of stems in perennial caulescent North American Viola species is uncommon and has been documented in ten species: V. adunca, V. canadensis, V. canina, V. douglasii, V. glabella, V. pedunculata, V. pinetorum, V. purpurea, V. quercetorum, and V. walteri. Branching in these species involves the development of one or more relatively short, leafy, axillary shoots on one or more stems.
The three annual species in the flora area, V. arvensis, V. bicolor, and V. tricolor, commonly branch from the base of the main stem near or at the crown and from nodes higher on the stem.
The leaves of acaulescent species develop from the rhizome. In homophyllous plants, all leaf blades are lobed from early season through late season; the depth of sinuses depends somewhat on the age of the plant. In heterophyllous plants, the earliest leaf blades are not lobed; later-season blades are lobed. E. Brainerd (1910, 1921) placed great emphasis on these morphological distinctions to differentiate Viola taxa. Like Brainerd, L. E. McKinney (1992) found these differences to be reliable taxonomic characters.
Here, the distal portion of the style is called the style head. The shape, size, position of the stigmatic surface, and degree of bearding vary among species. Differences among style heads have been used in Viola classification (W. Becker 1925; J. Clausen 1929) and in keys. Here, we report whether the style head is bearded or beardless based on reports in the literature and our observations. Of the 30 acaulescent species in the flora area, one has a bearded style; of the 43 caulescent species, 35 are always bearded, three are bearded or beardless, and five are always beardless.
Of the 73 species of Viola in the flora area, 60 are known to produce cleistogamous flowers, nine do not, and the condition in four is unknown. In some species of acaulescent A. Mayers and E. Lord (1983, 1983b) reported that pollen grains in cleistogamous flowers of V. odorata germinate in the undehisced anther sacs; the pollen tubes then penetrate the sac and grow towards the stigma. In other groups, observations suggest that pollen is released in proximity to the recurved style (T. Marcussen and T. Karlsson 2010).
Substantial research has been conducted on Viola pollination including cleistogamous flowers (A. J. Beattie 1969, 1969b, 1971, 1972, 1974, 1976, 1978; Beattie and D. C. Culver 1979; A. C. Cortés-Palomec and H. E. Ballard 2006; T. M. Culley 2000, 2002; G. Davidse 1976; L. Freitas and M. Sazima 2003; C. M. Herrera 1990; A. Mayers and E. Lord 1983, 1983b). Pollinator rewards available in most Viola flowers include nectar and pollen.
Pollinators of violets include bumblebees, honeybees, solitary bees, syrphid flies, butterflies, skippers, hawkmoths, moths, and beeflies. Thrips have been reported in Viola flowers (M. S. Baker 1935) and while these insects are often observed with pollen attached to their bodies, there is currently no evidence they play a role in pollination of Viola. Due to the high frequency that thrips, aphids, and other minute insects with pollen on their bodies have been observed in Viola flowers, it seems probable that these insects sometimes effect pollination.
The three valves of Viola capsules usually are thick in perennial species and thin in annual species. The capsules of at least some species open relatively slowly, exposing the seeds. As the valves dry, they contract and squeeze the seeds causing them to be ejected (R. J. Little and G. Leiper 2012). Capsules that disperse seeds ballistically are usually on erect peduncles; capsules that passively release their seeds usually point downward (A. J. Beattie and N. Lyons 1975).
Most Viola seeds possess an outgrowth (elaiosome), or food body, of variable size that is often attractive to ants. S. Lengyel et al. (2010) estimated that over 70% of Violaceae species are myrmecochorous. Studies have been conducted on various aspects of myrmecochory in Viola (A. J. Beattie and N. Lyons 1975; R. Y. Berg 1975; D. C. Culver and Beattie 1978, 1980; Beattie and Culver 1981; G. Matlack 1994).
Violets of horticultural importance include Viola arvensis (field or wild pansy), V. odorata (English or sweet violet), V. tricolor (Johnny-jump-up), and V. ×wittrockiana Gams ex Nauenburg & Buttler (garden pansy). Over 120 species of Viola are grown as ornamentals (L. Watson and M. J. Dallwitz, http://delta-intkey.com).
E. Brainerd (1908) reported that Viola chinensis G. Don (= V. patrinii de Candolle ex Gingins) was established at the New York Botanical Garden, at a residence in the District of Columbia, and in his garden in Massachusetts. It appears not to have persisted; it was not mentioned by N. Taylor (1915). A. Haines (2011) noted that reports of V. chinensis in New England were based on misidentifications of V. japonica.
Native Americans in the United States and Canada used Viola species for drugs, dyes, and food (D. E. Moerman 1998). Medicinal uses included pain relief and treatment of ailments including colds and coughs and for dermatological, gastrointestinal, eye, heart, and respiratory problems. Leaves and stems of some species were used as vegetables, usually cooked. Some tribes are reported to have soaked the seeds of corn in an infusion of violet roots before planting to repel insects.
Mature plants are often needed for identification of violets. In preparing specimens of violets, care should be taken to record data on petal and spur colors, and presence and distribution of beards on lateral and other petals, or note if lacking.
Measurements of the lowest petal in the descriptions here include the spur.
When this treatment was being finalized, Viola calcicola R. A. McCauley and H. E. Ballard was described as new. Time constraints prevented it from being incorporated. Viola calcicola is acaulescent, heterophyllous, has short, vertical rhizomes, nearly white to purple corollas, and occurs only on limestone substrates. It is endemic to the Guadalupe Mountains of Texas and New Mexico.
Species 400–600 (73 in the flora).
Selected References
Lower Taxa
Key
| 1 | Plants acaulescent | > 2 |
| 1 | Plants caulescent | > 34 |
| 2 | Style head bearded; Arizona. | Viola umbraticola |
| 2 | Style head beardless; not confined to Arizona | > 3 |
| 3 | Petals deep lemon-yellow. | Viola rotundifolia |
| 3 | Petals not lemon yellow | > 4 |
| 4 | Leaf blades lobed | > 5 |
| 4 | Leaf blades unlobed (mid-season incised or lobed at base only in V. sagittata) | > 13 |
| 5 | Leaf blades lobes similar in width and shape | > 6 |
| 5 | Middle and lateral blade lobes differ in width and/or shape | > 7 |
| 6 | All petals beardless; cleistogamous flowers absent. | Viola pedata |
| 6 | Lateral petals bearded, lowest sometimes bearded; cleistogamous flowers present. | Viola pedatifida |
| 7 | Mid-season leaf blades incised or lobed at base only. | Viola sagittata |
| 7 | Mid-season leaf blades incised or lobed throughout | > 8 |
| 8 | Earliest leaf blades lobed (plants homophyllous), similar to mid-season blades | > 9 |
| 8 | Earliest leaf blades unlobed, or sometimes 3-lobed (plants heterophyllous), mid-season blades lobed | > 10 |
| 9 | Middle lobes of leaf blades lanceolate or spatulate to narrowly obovate; plants usually glabrous; sepal auricles 2–3 mm. | Viola brittoniana |
| 9 | Middle lobes of leaf blades narrowly deltate to narrowly elliptic; plants usually pubescent; sepal auricles 1–2 mm. | Viola subsinuata |
| 10 | Mid-season leaf blades with 3–5 primary lobes, middle lobe elliptic, ovate, to widely ovate. | Viola palmata |
| 10 | Mid-season leaf blades with 5–9 primary lobes, middle lobe lanceolate, spatulate, to narrowly ovate | > 11 |
| 11 | Petioles, leaf surfaces, and peduncles rarely glabrous. | Viola palmata |
| 11 | Petioles, leaf surfaces, and peduncles rarely pubescent | > 12 |
| 12 | Earliest leaf blades ± deltate or 3-lobed; lowest petal 10–15 mm; plants of limestone glades and barrens. | Viola egglestonii |
| 12 | Earliest leaf blades ± ovate, sometimes 3-lobed; lowest petal 15–25 mm; plants of sandy, dry or seasonally wet pine or mixed pine-deciduous woods. | Viola septemloba |
| 13 | Lowest petal spur 3–10 mm | > 14 |
| 13 | Lowest petal spur 1–3 mm | > 17 |
| 14 | Capsules puberulent. | Viola odorata |
| 15 | Petioles not winged. | Viola selkirkii |
| 15 | Petioles narrowly winged distally | > 16 |
| 16 | Leaf base cordate. | Viola japonica |
| 16 | Leaf base usually truncate, sometimes ± cordate or broadly cuneate. | Viola prionantha |
| 17 | Leaf blades lanceolate, narrowly elliptic, linear, or ovate | > 18 |
| 17 | Leaf blades ovate to broadly ovate, reniform, orbiculate, elliptic, or deltate | > 19 |
| 18 | Leaf blades lanceolate or narrowly elliptic to nearly linear. | Viola lanceolata |
| 18 | Leaf blades elliptic to narrowly or broadly ovate. | Viola primulifolia |
| 19 | Plants stoloniferous | > 20 |
| 19 | Plants not stoloniferous | > 23 |
| 20 | Petals white | > 21 |
| 20 | Petals lilac, pale blue, violet, or deep purple, sometimes nearly white | > 22 |
| 21 | Lateral petals usually beardless; leaf blade margins serrate, ciliate or eciliate. | Viola blanda |
| 21 | Lateral petals usually bearded, rarely beardless; leaf blade margins ± entire or shallowly crenate, eciliate. | Viola macloskeyi |
| 22 | Bracteoles usually above middle of peduncle in chasmogamous flowers; leaf blade margins crenate, denticulate, or entire, ciliate or eciliate. | Viola epipsila |
| 22 | Bracteoles usually below middle of peduncle; leaf blade margins crenulate, eciliate. | Viola palustris |
| 23 | All petals beardless | > 24 |
| 23 | Lateral 2 and sometimes also lowest petals bearded | > 25 |
| 24 | Petals light violet on both surfaces; leaf blades ± deltate. | Viola clauseniana |
| 24 | Petals white on both surfaces; leaf blades reniform or ovate to broadly ovate or orbiculate. | Viola renifolia |
| 25 | Petals white. | Viola renifolia |
| 25 | Petals violet, light to dark blue-violet, lavender-violet, light to deep or dull reddish violet, dark purple-violet or reddish purple, or deep bluish violet, rarely white | > 26 |
| 26 | Sepal auricles 2–6 mm | > 27 |
| 26 | Sepal auricles 1–2 mm | > 28 |
| 27 | Leaf blade base reniform to cordate; plants of mesic to wet habitats. | Viola cucullata |
| 27 | Leaf blade base truncate, slightly sagittate or hastate, or ± cordate; plants of dry, sandy, open woods and thickets. | Viola sagittata |
| 28 | Adaxial leaf surface with silvery strigose patches. | Viola hirsutula |
| 28 | Adaxial leaf surface without silvery strigose patches | > 29 |
| 29 | Petioles densely pubescent | > 30 |
| 29 | Petioles glabrous or pubescent | > 31 |
| 30 | Leaf blades narrowly ovate to narrowly deltate; plants of wet, rocky shores of lakes and streams, meadows. | Viola novae-angliae |
| 30 | Leaf blades elliptic, ovate, or reniform; plants of sandy pine-oak or pine-oak-hickory woods and disturbed ground. | Viola villosa |
| 31 | Leaf blades ovate, broadly ovate, or reniform to broadly reniform or orbiculate | > 32 |
| 31 | Leaf blades narrowly ovate or narrowly deltate to broadly deltate | > 33 |
| 32 | Leaf blades somewhat fleshy, surfaces usually glabrous, grayish green or purplish green abaxially; plants of wet habitats in saturated soil; plants 5–15 cm. | Viola nephrophylla |
| 32 | Leaf blades not fleshy, surfaces usually pubescent, green abaxially; plants of dry or mesic habitats, not in saturated soil; plants 5–50 cm. | Viola sororia |
| 33 | Leaf blades sparsely pubescent, rarely glabrous adaxially; lower petal obviously bearded, rarely beardless. | Viola affinis |
| 33 | Leaf blades glabrous, rarely pubescent; lower petal beardless, rarely lightly bearded. | Viola missouriensis |
| 34 | Cauline stipules palmately lobed or pinnatifid, equaling leaf blade | > 35 |
| 34 | Cauline stipules unlobed, shorter than leaf blade | > 37 |
| 35 | Lateral petals ± equaling or shorter than sepals. | Viola arvensis |
| 35 | Lateral petals longer than sepals | > 36 |
| 36 | Sepal auricles 0.5–2 mm; style head bearded; cleistogamous flowers axillary. | Viola bicolor |
| 36 | Sepal auricles 2–4 mm; style head beardless; cleistogamous flowers absent. | Viola tricolor |
| 37 | Leaves compound | > 38 |
| 37 | Leaves simple | > 42 |
| 38 | Upper 2 and lower 3 petals light golden- to deep lemon-yellow | > 39 |
| 38 | Upper 2 petals dark reddish violet, lower 3 lilac, pale yellow, or cream, seldom white | > 40 |
| 39 | Leaf blades ovate, lobes 1–2.5(–5) mm wide; cleistogamous flowers absent; capsules glabrous. | Viola douglasii |
| 39 | Leaf blades reniform or ovate to ± orbiculate, lobes 2–10 mm wide; cleistogamous flowers axillary; capsules glabrous or puberulent. | Viola sheltonii |
| 40 | Lower 3 petals pale yellow, cream, or ± white. | Viola hallii |
| 40 | Lower 3 petals lilac, rarely white | > 41 |
| 41 | Abaxial leaf surface without distinct vein parallel to each margin, margins usually ciliate, surfaces usually puberulent; California, Idaho, Nevada, Oregon, Utah | Viola beckwithii |
| 41 | Abaxial leaf surface usually with distinct vein parallel to each margin, margins eciliate, surfaces glabrous; Oregon, Washington. | Viola trinervata |
| 42 | Plants stoloniferous; stems prostrate, spreading | > 43 |
| 42 | Plants not stoloniferous; stems erect, ascending, spreading, decumbent, or prostrate (sometimes later reclining to nearly prostrate in V. adunca, V. howellii) | > 44 |
| 43 | Petals lemon-yellow; cauline stipule margins entire or sparingly toothed. | Viola sempervirens |
| 43 | Petals pale to bluish violet; cauline stipule margins laciniate. | Viola walteri |
| 44 | Petals white or cream adaxially | > 45 |
| 44 | Petals not white or cream adaxially (sometimes almost white in V. frank-smithii; rarely white in V. adunca and V. labradorica) | > 48 |
| 45 | Basal leaf blades orbiculate-ovate to deltate, usually shiny, leathery, base cuneate; cauline blade base cuneate | Viola cuneata |
| 45 | Basal leaf blades ovate to reniform or deltate, not shiny or leathery, base cordate, subcordate, rounded, hastate, attenuate (oblique or not), or truncate; cauline blade base cordate to truncate | > 46 |
| 46 | Petals white or cream on both surfaces, without yellow patch basally, spur white, 3–6 mm. | Viola striata |
| 46 | Petals white on adaxial surface, with yellow patch basally, spur white, yellow, or greenish, 1–2.5 mm | > 47 |
| 47 | Spurs white, upper 2 petals, sometimes lower 3, usually tinged soft reddish violet, rarely white abaxially. | Viola canadensis |
| 47 | Spurs yellow or greenish, upper 2 petals, sometimes lower 3, deep reddish violet abaxially. | Viola ocellata |
| 48 | Petals blue to gray, violet to pale or soft blue-violet, pale to deep lavender-violet, soft reddish violet, or ± white adaxially | > 49 |
| 48 | Petals yellow adaxially | > 58 |
| 49 | All petals yellow basally | > 50 |
| 49 | All or just 3 lower petals white basally | > 51 |
| 50 | Leaf blades broadly reniform to ovate, base cordate; petals soft reddish violet; lowest petal 10–15 mm, spur yellow; Washington. | Viola flettii |
| 50 | Leaf blades broadly ovate, deltate, or broadly deltate, base cordate to truncate; petals blue to pale violet; lowest petal 5.5–11 mm, spur white to pale violet; Nevada, Utah. | Viola lithion |
| 51 | Spurs 10–20 mm; petals beardless; style head beardless. | Viola rostrata |
| 51 | Spurs 1.6–8 mm; lateral petals sparsely to densely bearded; style head bearded or beardless | > 52 |
| 52 | Lateral and upper 2 petals pale purple or almost white adaxially, violet abaxially; Utah. | Viola frank-smithii |
| 52 | Lateral and upper 2 petals similar color on both surfaces; not limited to Utah | > 53 |
| 53 | Basal leaves absent. | Viola canina |
| 53 | Basal leaves present | > 54 |
| 54 | Spurs 2–5 mm, tip straight | > 55 |
| 54 | Spurs 3–8 mm, tip straight, curved, or pointed, hooked | > 56 |
| 55 | Sepal margins ciliate or eciliate; style head bearded; seeds light brown. | Viola howellii |
| 55 | Sepal margins eciliate; style head usually beardless, sometimes bearded; seeds dark olive to ± black. | Viola langsdorffii |
| 56 | Sepal auricles enlarged in fruit. | Viola riviniana |
| 56 | Sepal auricles not enlarged in fruit | > 57 |
| 57 | Leaf blades usually decurrent on petiole; cauline stipule margins lacerate to laciniate. | Viola adunca |
| 57 | Leaf blades not decurrent on petiole; cauline stipule margins ± entire or laciniate. | Viola labradorica |
| 58 | Stems leafless proximally, leafy distally; style head bearded | > 59 |
| 58 | Stems leafy proximally and distally; style head bearded or beardless | > 63 |
| 59 | Cauline leaf blades widely or narrowly hastate to ovate, unlobed, usually mottled light green adaxially. | Viola hastata |
| 59 | Cauline leaf blades ovate, reniform, deltate, rhombic, ovate-orbiculate, or reniform-cordate, unlobed or 3–12-lobed, if deltate, not mottled light green adaxially | > 60 |
| 60 | Petals lemon-yellow on both surfaces; cauline blades unlobed | > 61 |
| 60 | Petals lemon-yellow adaxially, upper 2 and sometimes lateral 2 brownish purple abaxially; cauline blades unlobed or 3–12-lobed | > 62 |
| 61 | Cauline stipules ovate to oblong, margins erose or subserrate, often glandular, apex acute to acuminate; petioles 0.2–2.9 cm; blades ovate to deltate, base cordate to truncate, apex acute; Alberta, British Columbia, Alaska, California, Idaho, Montana, Oregon, Washington. | Viola glabella |
| 61 | Cauline stipules ovate, margins entire or coarsely serrate or erose, apex acute; petioles 1–10 cm; blades reniform or ovate to ovate-orbiculate or deltate, base cordate, apex acute to acuminate; c (incl. Wyoming), e North America. | Viola pubescens |
| 62 | Stems 1–3; basal leaves 0–2; cauline stipules sometimes ± leaflike; peduncles 2–13 cm; California, Oregon. | Viola lobata |
| 62 | Stems 1(–2); basal leaves 0(–2); cauline stipules not leaflike; peduncles 1.5–4 cm; e United States. | Viola tripartita |
| 63 | Basal leaves 0; style head bearded | > 64 |
| 63 | Basal leaves 1–11; style head bearded or beardless | > 65 |
| 64 | Petioles glabrous; leaf blades 1.2–2.4 cm, margins entire or with 1–3 crenations on proximal 1/2, eciliate; Texas. | Viola guadalupensis |
| 64 | Petioles usually finely puberulent, sometimes glabrate; leaf blades 1–5.5 cm, margins crenate to serrate, ciliate; California. | Viola pedunculata |
| 65 | Style head beardless. | Viola biflora |
| 65 | Style head bearded | > 66 |
| 66 | Cleistogamous flowers absent. | Viola tomentosa |
| 66 | Cleistogamous flowers present | > 67 |
| 67 | Capsules puberulent | > 68 |
| 67 | Capsules glabrous or finely puberulent | > 71 |
| 68 | Basal blade with prominent whitish veins adaxially; seeds black. | Viola charlestonensis |
| 68 | Basal blade without prominent whitish veins adaxially; seeds light to medium or dark brown or mottled gray and brown | > 69 |
| 69 | Capsules 8–12 mm. | Viola quercetorum |
| 69 | Capsules 3.5–7 mm | > 70 |
| 70 | Cauline blades 2.8–9.6 × 0.3–1.4 cm, length 4–11 times width. | Viola pinetorum |
| 70 | Cauline blades 0.9–5.2 × 0.2–2.9 cm, length 0.8–7.1 times width. | Viola purpurea |
| 71 | Capsules ellipsoid to oblong | > 72 |
| 71 | Capsules spherical, subglobose, or ovoid | > 73 |
| 72 | Base of basal and cauline leaf blades cordate; upper 2 petals deep lemon-yellow abaxially.Viola orbiculata | > 72 |
| 72 | Base of basal and cauline leaf blades attenuate to ± truncate or subcordate; upper 2 petals brownish purple abaxially. | Viola praemorsa |
| 73 | Basal leaf base usually truncate, sometimes attenuate. | Viola vallicola |
| 73 | Basal leaf base attenuate (rarely truncate or subcordate in V. utahensis) | > 74 |
| 74 | Basal blade margins ± coarsely crenate-serrate. | Viola utahensis |
| 74 | Basal blade margins entire or serrulate, sometimes with a few sharp teeth or crenulate | > 75 |
| 75 | Elaiosome not covering funiculus; basal and cauline leaf surfaces glabrous or puberulent on margins or veins. | Viola bakeri |
| 75 | Elaiosome completely covering funiculus; basal and cauline leaf surfaces glabrous or puberulent. | Viola nuttallii |