Northern Ontario Plant Database

Plant Description

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The Genus Viola

Violaceae (Violet Family)

Violets, the genus Viola, are often thought to be a difficult group to identify since they are morphologically diverse and are known to hybridize, which further confuses identification. Gray's Manual of Botany (Fernald 1950), describes 51 species of Viola from central and northeastern U.S. and adjacent Canada. Fortunately, many of these species have recently been combined, making identification much easier. But to correctly identify violets to the species level, an understanding of the variation found in stems, leaves, flowers, and fruits is necessary.

Violets have two basic growth forms, based on whether their stems are underground or above-ground. Stemless violets have underground stems (rhizomes) that give rise to a crown of basal leaves and flowers; the rhizomes may be slender or short and stout, and oriented horizontally or vertically. Stemmed violets have above-ground stems that may be erect or creeping; both have leaves borne along the length of the stem (cauline leaves) in an alternate arrangement, with flowers borne in the axil of the leaf and stem (axillary flowers). Both stemless and stemmed violets may also produce long thin runners (stolons), which spread just beneath the surface and may produce extensive colonies. The presence or absence of stolons is very diagnostic in some species.

Violet leaves are petioled, with a pair of stipules borne at the base of each petiole. Most people picture heart-shaped (cordate) leaves when they think of violets, but blade shape in violet leaves ranges from cordate or reniform to narrowly lanceolate, or even deeply divided into several narrow lobes. However, the cordate leaf shape is the most common and northern Ontario species all have simple, undivided leaf blades. Leaf blade shape will also vary between young and mature leaves, with younger leaves often more reniform with blunter apices than mature leaves, so look at the most mature leaves on the plant when determining leaf shape. Leaf margins are crenate, with rounded teeth; these teeth may be low or prominent and, from a side view, the margins may be either flat or somewhat wavy (undulate).

Flowers are solitary at the end of stalks (peduncles), with 5 green sepals and 5 petals that may be purple, pale blue, yellow, or white. Some or all of the petals may be bearded, bearing straight or club-shaped (clavate) hairs at the base of the petals, or they may all be beardless. Aside from the differences in colour and bearding, violet flowers share the same basic anatomy. The flowers are slightly irregular, with two upper petals, two lateral petals, and one lower petal that bears a spur at the base; spurs may be short and barely noticeable or long (nearly 2 cm in length). The lower petal and sometimes the two lateral petals are often lined with dark blue to purple veins. The narrow sepals each bear a small lobe, called an auricle, that projects backward from the sepal attachment. Sepals may have margins lined with short, straight hairs (ciliate margins) or the margins may be entire (eciliate); sepals are persistent in fruit. Some flowers are fragrant, but most have no odour.

The 5 stamens have short filaments, which end in triangular-shaped appendages above the anthers; the anthers and appendages are connivent around the style, which means they surround the style, touching, but are not fused to each other. The two lower stamens are spurred, with the spurs hidden within the lower petal spur. The superior ovary is compound, composed of 3 carpels, but with a single locule. The style is thicker at the top (clavate) and topped by a small stigma placed off centre (oblique). Placentation is parietal, with ovule attached along the carpel edges, which protrude slightly into the locule.

The 3-carpelled ovary develops into a capsule that splits (dehisces) into 3 boat-shaped segments called valves. The capsule dehisces through the locules (loculicidal capsule), exposing the seeds, which are attached to the placental region along the mid-line of each valve. The numerous smooth round or ovoid seeds are expelled from the dehisced capsule as the walls of each valve press firmly together from the base upward, forcibly squeezing the seeds out of the capsule segments. Seeds range in size from 1–4 mm long and may be buff, olive-brown, or black in colour. Violet seeds bear a small fleshy appendage (0.2 to 1 mm long), called a caruncle, at the point of attachment to the placenta (hilum). The caruncle is nutrient-rich and attractive to ants, which disperse the seeds.

Violets also bear small, self-pollinating flowers, called cleistogamous flowers or cleistogenes, that lack petals and do not open; these flowers fertilize and set fruit while still in bud. Compared to the petal-bearing (petaliferous) flowers, cleistogamous flowers are much smaller and the shape of their sepals may differ greatly from those of the petaliferous flowers.

There are 15 species of violets native to northern Ontario. Because of the diverse leaf shape and floral characters, we will divide the violets into smaller, more manageable groups to discuss. The first and most easily recognizable trait we use to divide the violets is the whether the plants are stemmed or stemless. Remember, stemless violets have a short underground rhizome with a crown of basal leaves and flowers, while stemmed violets have an erect or creeping above-ground stem that bears alternate cauline leaves and axillary flowers. Next, we divide the violets according to petal colour, basically purple, and white or yellow. These resulting 4 groups, shown in Table 1, are then separated out to species in the keys provided. When trying to identify a violet, once you have determined the petal colour and whether your plant is stemmed or stemless, the most important characters to take note of are:

– the number of bearded petals (0–5)
– the shape of the beard hairs (straight or swollen at the tips)
– the presence or absence of hairs along the margins of the sepals (ciliate or eciliate)
– the length of the spur on the lower petal (short or long spurred)
– the presence or absence of hairs on the upper or lower leaf surfaces and peduncles
– the presence or absence of stolons (slender runners that spread just below the surface).

These traits are all used in the following keys and descriptions. Please note that violet species often hybridize, so plants that do not clearly fit the keys or descriptions may be hybrids.

The nomenclature used in the NOPD checklist and in the keys & charts below follows Ballard's Violets of Michigan (1994). Other treatments of the genus Viola have been developed that lump many of the blue stemless violets together (McKinney & Russell 2002), but we believe Ballard's treatment is more logical, especially ecologically, and fits well with the taxa observed in northern Ontario.

Table 1. Viola Species in Northern Ontario.
The violet species in northern Ontario are divided in this table into 4 main groups, based on the presence or absence of above-ground stems and flower colour. For convenience, the 8 stemless blue species are subdivided into 2 groups, based on whether the plants are smooth (glabrous) or hairy (pubescent). The species in each of these units can be identified using the keys or comparison charts listed under each of these species groups.

	stemless species	stemmed species
blue to purple flowers	plants hairy Viola novae-angliae Viola selkirkii Viola sororia Go to Key 1 Go to Comparison Chart 1 plants glabrous Viola affinis Viola cucullata Viola nephrophylla Viola palustris Viola epipsila subsp. repens Go to Key 1 Go to Comparison Chart 2	Viola adunca Viola labradorica Go to Key 3 Go to Comparison Chart 4
white or yellow flowers	Viola blanda Viola macloskeyi Viola renifolia Viola lanceolata Go to Key 2 Go to Comparison Chart 3	Viola canadensis Viola pubescens Go to Key 3 Go to Comparison Chart 4

Viola Comparison Chart 1
Northern Ontario Stemless Blue Violets with Hairy Leaves

Viola sororia (woolly blue violet)	Viola novae-angliae (New England violet)	Viola selkirkii (great-spurred violet)
plants lacking stolons		plants with stolons
leaves ovate-cordate with obtuse to somewhat acute apices in later leaves; leaves hairy on both surfaces; petioles & peduncles hairy	leaves narrowly triangular- ovate, longer than wide; apex acuminate; leaves glabrous above, hairy beneath; petioles & peduncles hairy at base	leaves broadly cordate; inner margins of bases touch or overlap; leaves hairy on upper surface, glabrous beneath; petioles & peduncles glabrous
lateral 2 petals bearded with straight hairs; upper 2 petals beardless, or bearing few, scattered hairs		all petals beardless
spurred petal beardless (or some with a few hairs)	spurred petal bearded
spur short		spur long, 5-7 mm
sepals oblong-ovate, apices obtuse		sepals narrowly lanceolate, apices acuminate
sepal margins ciliate and auricles ciliate	sepal margins and auricles eciliate
capsules ovoid, purplish or purple-mottled; peduncles prostrate to arching; seeds buff to brown	capsules nearly globose, purple-mottled, peduncles prostrate to arching; seeds buff	capsules ellipsoid to nearly globose, green, purple-mottled; peduncles ascending; seeds buff
mesic sugar maple forests, other dry-mesic hardwood & mixedwood forests; common on lawns, trails, meadows, slopes.	only in western Ontario; open mixed hardwood and coniferous forests; sand or rocky shores, streambanks (the most xeric habitat).	rich, shaded woods, usually in areas with basic soils or calcareous substrates.

Viola Comparison Chart 2
Northern Ontario Stemless Blue Violets with Glabrous Leaves

V. nephrophylla (northern bog violet)	V. affinis (LeConte's violet)	V. cucullata (marsh blue violet)	V. palustris & V. epipsila
plants lacking stolons			plants with stolons
leaves broadly cordate to reniform; apices obtuse to rounded; glabrous on both surfaces	leaves triangular-ovate, apices acuminate; glabrous on both surfaces	leaves cordate, longer than broad; apices acute to acuminate; glabrous on both surfaces	leaves broadly cordate, orbicular, to reniform; apices rounded to acute; glabrous on both surfaces
corolla deep purple, with a white throat; not fragrant		corolla lilac to purple, often with a darker ring around the white throat; not fragrant	corolla pale lilac or lavender to grayish, with dark purple veins; very fragrant
lateral 2 petals bearded with straight hairs, upper 2 petals beardless, spurred petal bearded		lateral 2 petals bearded with clavate hairs, upper 2 and spurred petals beardless	lateral 2 petals beardless to slightly bearded; upper 2 and spurred petals beardless
spur short
sepals lanceolate to ovate, apices obtuse	sepals lanceolate, apices acuminate		sepals ovate to lance-ovate, apices obtuse
sepal margins & auricles not ciliate
capsules ellipsoid, green; peduncles erect; seeds buff to blackish	capsules ellipsoid,green to purple-mottled; peduncles ascending; seeds buff	capsules long-ovoid, green, peduncles erect, seeds blackish	capsule ellipsoid, green; seeds buff.
wet calcareous sedge meadows, peatlands, wet limestone barrens	deciduous swamps, bottomlands, floodplains, wet shores, streambanks	wet swampy areas, marshes, sedge meadows, bogs	cool, alpine to subalpine moist meadows and slopes, alpine brooksides

Viola Comparison Chart 3
Northern Ontario Stemless White Violets

Viola blanda (sweet white violet)	Viola renifolia (kidneyleaf violet)	Viola macloskeyi (northern white violet)	Viola lanceolata (lanceleaf violet)
plants generally hairy (pubescent), leaves hairy when young; variously hairy to glabrous at maturity		plants smooth (glabrous),leaves smooth on both surfaces
leaves broadly cordate to reniform; lateral petals bearded	lateral petals beardless or nearly so
plants with stolons	plants lacking stolons	plants with long, slender stolons
leaves cordate, mature leaves with blunt to pointed tips.	leaves rounded (orbicular) to kidney-shaped (reniform), mature leaves with flat to rounded tips.	leaves broadly cordate to rounded (orbicular), mature leaves with blunt to rounded tips.	leaves narrowly lanceolate or oblanceolate, blunt at the tip and tapering at the narrow base.
lower leaf surfaces noticeably paler; upper leaf surfaces shiny if glabrous; or dull and pubescent.		lower leaf surface not paler; petioles often bearing long hairs.

Viola Comparison Chart 4
Northern Ontario Stemmed Violets

Viola labradorica (Labrador violet)	Viola adunca (hooked violet)	Viola canadensis (Canada violet)	Viola pubescens (yellow violet)
petals lavender	petals deep violet	petals white, tinged with violet on back	petals yellow
stems creeping to spreading		stems erect
plants glabrous	plants hairy (glabrous in var. glabra)	plants glabrous to hairy
spur 4-5 mm long	spur 4-6 mm long	spur short

Key 1: Key to the Purple Stemless Violets of Northern Ontario

1a.	Plants with mostly narrowly triangular leaves at flowering time (anthesis), blades longer than wide.		go to 2
1b.	Plants with cordate to reniform leaves at anthesis, blades wider than long.		go to 3
	2a.	Leaf blades and petioles smooth (glabrous); sepals with pointed (acute) tips, sepal margins often ciliate – bearing short, straight hairs, or not ciliate; capsules ellipsoid; plants of moist to wet habitats, low woods; widespread in northern Ontario, reported to about 51°N (James Bay watershed).
	Viola affinis (LeConte's violet, sand violet)
	2b.	Leaf blades glabrous above, hairy beneath and along petiole bases; sepals with blunt (obtuse) tips, sepal margins not ciliate; capsules nearly round (globose); plants of dry habitats (our most xeric species); in Ontario, restricted to western Ontario (known from Quetico Park).
	Viola novae-angliae (New England violet)
3a.	Plants with hairy leaves and peduncles; at least the upper leaf surface hairy.		go to 4
3b.	Plants with glabrous leaves and peduncles, at least when mature.		go to 5
	4a.	Leaf blades with rounded basal lobes that nearly touch or overlap; the inner margins of the lobes curve inward, towards the petiole; only the upper leaf surface hairy, petals all beardless, lower petal with a long, prominent spur; sepal margins eciliate; plants of rich habitats, particularly over calcareous substrates, also at the base of cinder-block constructions (which leach lime).
	Viola selkirkii (great-spurred violet, Selkirk's violet)
	4b.	Leaf blades with rounded basal lobes that do not overlapping, the inner margins of basal lobes curve outward, away from the petiole; leaves and peduncles hairy, at least lateral petals heavily bearded; lower petal with a short spur; sepal margins ciliate; plants of non-calcareous habitats, including sugar maple and mixedwood forests, grassy meadows and slopes, lawns, and trails.
	Viola sororia (woolly blue violet)
5a.	Plants lacking stolons; at least the lateral petals bearded; flowers not fragrant; plants not restricted to arctic-alpine habitats.		go to 6
5b.	Plants spreading by stolons; petals all beardless or the lateral petals slightly bearded; flowers fragrant; plants of moist to wet arctic-alpine habitats.		go to 7
	6a.	Lateral petals of flowers bearded with short, club-shaped hairs, spurred petal beardless; sepals with sharply pointed (acuminate) tips; plants of wet, non-calcareous habitats, including stream margins, wet meadows, bogs.
	Viola cucullata (marsh blue violet)
	6b.	Lateral petals of flowers bearded with fine, straight hairs, spurred petal usually bearded, at least with a few hairs; sepals with obtuse to rounded tips; plants of calcareous habitats, including gravelly shores, marly bogs, moist to wet limestone barrens, fields and meadows over limestone or dolomite bedrock.
	Viola nephrophylla (northern bog violet)
7a.	Plants with 3 or more leaves present at anthesis; flowers lilac, grayish, to nearly white, with at least the spur purplish; stipules with slightly ciliate margins.
Viola palustris (alpine marsh violet)
7b.	Plants with 1 or 2 leaves present at anthesis; flowers lilac; stipules lacking ciliate margins.
Viola epipsila (northern marsh violet, dwarf marsh violet, creeping marsh violet)

Key 2: Key to the Stemless White Violets of Northern Ontario

1a.	Plants with narrow lanceolate leaves; the blade tapering to the petiole (attenuate) , not lobed at the base.
Viola lanceolata (lanceleaf violet)
1b.	Plants with wider, cordate, ovate, to reniform leaves, bases cordate.		go to 2
	2a.	Lateral petals usually obviously bearded; peduncles hairy; leaves and petioles somewhat to very hairy, often hairy on just the lower leaf surface; mature leaf tips acute; plants of moist forest habitats.
	Viola blanda (sweet white violet)
	2b.	Lateral petals beardless, or at most bearing a few tufts of hair; peduncles glabrous; leaves and petioles glabrous to somewhat hairy at the base; mature leaf tips flat (truncate), blunt (obtuse), or rounded; plants of moist to wet habitats.
	go to 3
3a.	Plants with thin stolons, leaves and peduncles glabrous, petioles often bearing scattered, long hairs; leaf blades dull above, not paler on the lower surface; flowers somewhat fragrant; petals beardless, or rarely the laterals with a few scattered hairs; plants of acidic substrates.
Viola macloskeyi (northern white violet)
3b.	Plants without stolons; lower leaf surface and peduncles hairy; leaf blades shiny and glabrous above, under surface noticeably paler, flowers not fragrant; petals beardless; plants of moist to wet habitats on calcareous substrates, such as ravines in limestone barrens or cedar swamps over limestone bedrock.
Viola renifolia (kidneyleaf violet)

Key 3: Key to the Stemmed Violets of Northern Ontario

1a.	Flowers blue, purple, or lavender, long-spurred, stems low and spreading.		go to 2
1b.	Flowers yellow or white, short-spurred, stems erect.		go to 3
	2a.	Leaves light green, flowers lavender, plants of moist meadows and forest habitats; plants glabrous.
	Viola labradorica (Labrador violet)
	2b.	Leaves dark green to bluish-green, flowers lilac to purple, plants of well-drained, sandy or rocky habitats; plants hairy, with fine short hairs on the leaves and petioles (plants glabrous in var. glabra).
	Viola adunca (hooked violet)
3a.	Flowers yellow.
Viola pubescens (downy yellow violet)
3b.	Flowers white, often tinged with violet on the back of petals.
Viola canadensis (Canada violet)

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