Perennial herb 15 - 50 cm tall Leaves: opposite, stalkless, longer than wide, 2 - 5 cm long, 0.8 - 2.5 cm wide, egg- to lance-shaped with either blunt or pointed tips, but rarely sharp-pointed tips. The lower leaves are almost hairless, while the upper leaves are sparsely glandular-hairy, and fringed with slender bristles. Inflorescence: terminal, loose and open branched, covered with fine, gland-tipped hairs, and having nine to thirty flowers. The two lowest branches of the inflorescence are usually at least 1 cm long, and normally subtended by a pair of short, narrow, opposite bracts. Flowers: short-stalked, light violet to lavender, though occasionally white, 2 - 3 cm wide, radially symmetric, with a very slender tube, and abruptly flared lobes. The flowers often have a delicate, and sweet odor. Sepals: five, 0.6 - 1.1 cm long overall, but fused for up to half their length, then separating into linear lobes with awl-shaped tips up to 0.5 mm long. Petals: five, but fused into a 1.1 - 2 cm long, hairless tube, then separating into 1 - 1.5 cm long, 0.6 - 1 cm wide, inversely egg-shaped lobes, which usually have a notched tip up to 3 mm deep. Stamens: five, with filaments attached at different heights along the inside of the petal tube, but never extending beyond the petal tube. Pistil: with a single, three-chambered, superior ovary; and three, short (1.5 - 3 mm long, usually shorter than stigmas or ovary), fused styles, which separate about midway into three, linear stigmas. Fruit: a three-valved, three-chambered, egg-shaped capsule with one (rarely two), relatively large (2 - 6 mm long), ellipsoid seed per chamber. Stems: softly long-hairy, low, decumbent, trailing on the ground and rooting at the nodes, with erect, leafy, flowering shoots.
Similar species: Phlox divaricata is similar to P. pilosa and its subspecies, but those taxa have abruptly narrowed, sharp, stiff leaf tips; usually hairy petal tubes; and sepals with very long, pointed tips. There are two subspecies of P. divaricata: the typical subspecies, P. divaricata ssp. divaricata, as described above, which is less common in the Chicago Region; and P. divaricata ssp. laphamii, which has mostly non-toothed, rounded petal tips, which very rarely may be slightly notched. Other species of Phlox in the Chicago Region are either low, decumbent plants, or the style is very long, and much exceeds the length of the stigmas or ovary.
Flowering: April to June
Habitat and ecology: Very common in rich woodlands, and capable of tolerating moderate or even severe levels of disturbance.
Erect or decumbent at base, 3-5 dm, with decumbent basal stolons; lvs lance-ovate to oblong, 3-5 cm, obtuse or acute but not sharp-pointed; infl a loosely branched, glandular- hairy cyme, the branches on distinct peduncles, the pedicels often 5-10 mm; cor usually pale blue-purple, varying to red-purple or white, 2-3 cm wide, the glabrous tube 1-2 cm; style short; 2n=14. Rich moist woods; nw. Vt. and adj. Que. to Minn., s. to Ga. and Tex. Apr.-June. Var. divaricata, with the cor-lobes notched at the tip, is eastern, ranging w. to Mich. and e. Ill. Var. laphamii A. W. Wood, with entire cor-lobes, is more western, but occasional plants in the range of one var. have the cor-lobes of the other.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.