Rhizomatous perennial; stems 1-3 dm, finely and closely puberulent, tending to creep at base or to produce prostrate lower branches, otherwise simple; lvs mostly opposite, elliptic to broadly ovate, 1-2.5 נ0.5-1.5 cm, rounded to acutish, glabrous to nearly so, slightly toothed or entire; fls pedicellate in elongating terminal racemes, at least the upper bracts generally alternate; cor 4-8 mm wide; style 2-3.5 mm; fr finely and sometimes sparsely glandular-hairy, evidently notched, 3-4 mm, broader than high; seeds numerous, under 1 mm; 2n=14. Nearly cosmopolitan. May-Aug. Var. serpyllifolia, native of Europe, and established in fields, meadows, and lawns throughout our range, or even appearing native in open woods, has pale fls with blue lines, finely and closely puberulent pedicels, and filaments 1-2.5 mm. Var. humifusa (Dicks.) M. Vahl, irregularly distributed in moist woods and alpine meadows, and native in our range from N.S. and n. N.Y. to n. Mich. and n. Minn., has bright blue fls, the pedicels with some spreading, viscid or glandular hairs, the filaments 2-4 mm. (V. humifusa; V. tenella)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
