This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The habitat of this violet is calcareous ground. The plant was formerly regarded as a variety of Viola hirta. It is small, glabrous, without stolons. The rootstock is branched, thick, woody. The leaves are small, egg-shaped, oblong, heart-shaped. The flower-stalks are longer than the leaves. The flowers are very small, violet or mauve, the throat the same. The petals are narrow, the 4 upper forming a St. Andrew's cross, the sepals oblong to egg-shaped. The spur is very short, straight, conical. The capsule is small, roundish, depressed. It is a herbaceous perennial plant, flowering in April and May.
The habitat of this species is elevated calcareous pastures. The habit is tufted. The rootstock is thick, woody, brown, clothed with bases of earlier leaves. The stipules below are small and narrow, nearly entire, the upper ones longer, broader, hairy. The leaves are short-stalked, rounded, kidney-shaped, broadly heart-shaped, with a short point, thick, dotted, nearly entire. The flowers are large, blue, the anterior petal long, narrow, notched, with a blunt point. The spur is short, thick, furrowed. The sepals are hardly acute. The bracts are slender, entire, or above the curvature of the flower-stalk. The anther-spurs are very slender, sickle-like, as long as the anther, which has a blunt scale. The capsule is downy. The plant is 1-3 in. high, flowering in May, and is a herbaceous perennial.
The habitat of this species is mountain pastures, hilly districts. The plant has been regarded as a sub-species of V. tricolor, L. The habit is ascending-. The stem is branched and thread-like underground. The rootstock is slender, branched, the branches slender, with short stems and underground runners. The leaves are scalloped, toothed, the lower egg-shaped or lance-shaped. The stipules are lobed, linear, 3 lateral one side, 1 on the other, the middle one entire and larger, divided nearly to the base, the lobes radiating from a centre. The flowers are all yellow (hence lutea), the petals spreading, longer than the sepals. The capsule is round. The plant is 4-9 in. high, flowering from June till August, and is a perennial at high elevations or annual.