Perennial herb 35 cm - 1.25 m tall Leaves: stalkless, opposite, in ten to fifteen pairs, about ten times longer than wide (the largest 7.5 - 15 cm long and 0.5 - 2 cm wide), not veiny, usually smooth and hairless, though sometimes slightly roughened. The lower leaves are linear, while the upper leaves are broader and normally lance-shaped, but both have sharp, pointed tips. Inflorescence: of a single or few, terminal, flat or broadly rounded, wider than tall, open, multiple branched clusters with 25 to 125 flowers on individual short (only to about 0.5 cm long) stalks. The lower branches of the inflorescence are somewhat axillary, and long-stalked. Flowers: 1.5 - 2 cm wide, purple to pink (rarely white), sometimes with purple stripes near the center, radially symmetric, with a slender tube, and abruptly flared lobes. There is a faint fragrance to the flowers. Sepals: five, 6 - 7.5 mm long overall, but fused for almost two-thirds their length, then separating into narrow-triangular, 1.5 - 3 mm long lobes with very narrow, hard, bristle-like tips. Petals: five, but fused into a 1.5 - 2.2 cm long tube, then separating into 0.8 - 1.3 cm long, 6 - 1.1 cm wide, inversely egg-shaped lobes with non-toothed, or merely irregularly shallow-toothed tips. Stamens: five, with filaments attached at different heights along the inside of the petal tube, and about the same length as the petal tube, but not extending far beyond it. Pistil: with a single, three-chambered, superior ovary; and three, elongate (about 1.5 cm long, sometimes extending beyond petal tube), fused styles, which separate for only 0.5 - 1 mm before ending in three, linear stigmas. Fruit: a three-valved, three-chambered, egg-shaped capsule with one or several, 3.5 - 6 mm long, ellipsoid seeds per chamber. Rhizome: short, thick, and sending up stems from numerous and irregularly spaced nodes. Stems: erect, rarely sterile, with at least eight nodes below the inflorescence, occasionally sparsely short-hairy above, and sometimes with horizontal, prostrate, non-woody branches (stolons) at the base.
Similar species: Phlox glaberrima ssp. interior is most similar to P. maculata, but that species has a slender rhizome, and a narrow, longer than wide inflorescence. Also somewhat similar is P. paniculata, but that species has very veiny leaves with bristly hairs on the leaf edges. This is one of three subspecies of P. glaberrima, but the others occur more south and east of the Chicago Region. The other subspecies tend to have longer sepals (at least 8 mm long). The remaining species of Phlox in the Chicago Region either have obvious notched tips on the petals, or very short styles.
Flowering: June to early September
Habitat and ecology: Common in moist prairie remnants, wet calcareous meadows, and more rarely in drier prairies.
Occurence in the Chicago region: native
Notes: This plant has been observed to attract butterflies.
Author: The Field Museum
From Flora of Indiana (1940) by Charles C. Deam
Infrequent in prairie habitats in the northwestern part of the state and in the Illinoian area, especially in the southwestern part of the state, in hard, clay soil in low woods. Usually frequent to even common where it is found. Generally in low, wet woods and along roadsides in southern Indiana, and mostly along roadsides and railroads in the northwestern part. I collected an albino form of this species which I planted and it has done well in cultivation for nearly four years. It seems to prefer a slightly acid soil. Wherry divides this species into two varieties, a northern and a southern one, as follows: Sepals 5.5-7.5 mm long, united to about two thirds their length; calyx lobes thus 1.5-3 mm long = P. glaberrima var. interior Wherry. Sepals 6.5-8.5 mm long, united a half to two thirds their length; calyx lobes thus 2.5-4 mm long = P. glaberrima var. melampyrifolia (Salisbury) Wherry. The first variety is the northern form of the species and extends as far south as Kentucky, hence all Indiana plants belong to this variety. The second variety is the southern representative of this species and has not yet been found as far north as Indiana.