7a. Viola biflora Linnaeus var. biflora
Arctic yellow or northern yellow or twinflower violet, violette à deux fleurs Arctic yellow or northern yellow or twinflower violet, violette à deux fleurs
Plants 3–20 cm. Basal leaf blades 0.5–3[–3.5] × 0.9–3.5[–5] cm. Flowers: sepals usually without purple stripe; lowest petal 6–10 mm. Seeds 1.5–2 mm. 2n = 12.
Flowering Apr–Jul. Montane and arctic regions, tundra, mesic alpine meadows, scree slopes, grassy places in shade of alders and willows, lake margins, granite outcrops, moist coniferous forests, along streams and falls in wet moss, alluvial soil, sand; 40–3900 m; B.C., Yukon; Alaska, Colo.; c, s Europe; Asia (c, n China, ne India, Indonesia [n Sumatra], Japan, North Korea, Malaysia, Mongolia, Pakistan, Philippines, Russia, Siberia, Taiwan).
In North America, var. biflora occurs in Alaska (45–3300 m; PNW Herbaria Portal 2010), Yukon (1200–1500 m), and nine counties in central Colorado (1950–3850 m).