From Flora of Indiana (1940) by Charles C. Deam
This species has a wide range of habitats. It is generally found in dry soil on the crests and slopes of black and white oak ridges, in dry fallow fields, and in dry soil along roadsides and railroads. It is also found in moister situations but usually in sandy or hard, sandy, clay soil along roadsides and in prairie habitats. This species is likely to be confused with Pycanthemum virginianum, from which it may be distinguished easily by being glabrous or nearly so, and by having long, glabrous calyx teeth. Pycnanthemum virginianum is generally pubescent, and its calyx teeth are merely acute and generally long white-pubescent to the tip.
Nearly inodorous; stems 5-8 dm, very leafy, with many short axillary branches; herbage glabrous; lvs linear, entire, those of the main axis 2-5 cm נ2-4 mm; lateral veins 1-2(3) pairs, all arising in the basal fourth of the lf; heads very numerous and dense, hemispheric 3-8 mm wide, on peduncles 3-15 mm; outer bracts lanceolate, sometimes surpassing the heads; inner bracts numerous, closely appressed, about as long as the cals, firm, lanceolate, long-acuminate, the conspicuous midvein produced into a stiff, subulate point; cal-lobes narrowly triangular, acuminate, puberulent, usually 1-1.5 mm; cor 5-8 mm; 2n=80. Chiefly in dry soil of upland woods and prairies; Me. to Fla., w. to Minn., Kans., Okla., and Tex. (P. flexuosum, misapplied; P. linifolium)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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