Annual herb 10 - 50 cm tall Stem: erect, covered with long, soft, and usually glandular hairs. Leaves: opposite and stalked in the lowest three to five pairs, but then alternate, stalkless, and somewhat clasping in the upper pairs. All the leaves are hairy, longer than wide, 3 - 7.5 cm long, 1 - 2 cm wide, and pointed at the tip, but the lower leaves taper to the base, while the upper leaves are widest near the base or at least below their middles. Inflorescence: branching from the top of stem, each branch further branching, with those secondary branches subtended by a pair of linear, opposite bracts. The final branches have three to four flowers per branch tip, and each flower is on a short (up to 0.5 - 1 cm long) stalk. Flowers: reddish purple, about 2 cm long, about 2.5 cm wide, radially symmetric, with a very slender tube, and abruptly flared lobes. Sepals: five, 0.8 - 1.2 cm long overall, but fused for less than half their length, then separating into linear lobes with a slender, up to 1.5 mm long, stiff, bristle tip. The sepals are covered with long, soft, typically glandular hairs. Petals: five, glandular-hairy, but fused into a 1.3 - 1.7 cm long tube, then separating into broad, inversely egg-shaped, about 1 cm long, 0.9 cm wide lobes with a blunt, or sometimes an abruptly pointed tip. Stamens: five, with filaments attached at different heights along the inside of the petal tube, but rarely extending beyond the petal tube. Pistil: with a single, three-chambered, superior ovary; and three, short (2 - 3 mm long, less than half the length of the sepals), fused styles, which separate below or at the middle into three, linear stigmas. Fruit: a three-valved, three-chambered, egg-shaped capsule with one (rarely two), relatively large (to 6 mm long), ellipsoid seed per chamber. Root: normally a single, somewhat short, slender, and delicate taproot.
Similar species: Phlox drummondii is the only annual species of Phlox in the Chicago Region. It could possibly be confused with P. divaricata or P. pilosa and their subspecies, but those taxa are perennials, and their upper leaves are opposite, or closely so.
Flowering: spring and early summer
Habitat and ecology: Very rarely escaping from cultivation in our area.
Occurence in the Chicago region: non-native
Notes: This species is native to the coastal plain area of Texas.