Erect perennial to 15 dm, with 10-34 nodes below the infl, often branched at the top and bearing several racemes 5-15 cm; lvs all sessile, or the lowest 1-7 pairs petiolate but soon deciduous; sessile lvs 2-18 cm, mostly oblanceolate or elliptic, generally not clasping, sharply or less often bluntly toothed, rarely entire; upper lvs scarcely to evidently reduced; raceme-axis short-hairy and sometimes also stipitate-glandular; cal often glandular-punctate and sometimes also stipitate-glandular; cor (14-)16-35 mm, densely puberulent to glabrous, not glandular; 2n=38. In a wide range of mostly ±open habitats; Me. and Que. to Man. and N.D., s. to Fla. and n. Mex., seldom near the coast except as an escape from cult. July-Sept. Highly variable, here divided into 2 well marked geographic vars.: The relatively northern var. virginiana, seldom occurring as far s. as Va., Tenn., Mo., and Kans., is generally clonal, with the stems scattered on long, horizontal rhizomes; it lacks empty floral bracts below the infl. (P. denticulata; P. formosior) The relatively southern var. arenaria Shimek, seldom occurring n. to n. O., n. Ill., and Io., generally has the stems clustered on a short caudex (without long rhizomes), and very often has some empty floral bracts below the infl; it typically grows in drier sites than var. virginiana. (P. praemorsa; P. v. ssp. praemorsa; P. v. var. reducta; P. serotina) Many garden and escaped plants are ±intermediate, with the rhizomes of var. virginiana and the empty bracts of var. arenaria, but primary intergradation occurs mainly in c. and e. Tenn., c. and e. Ky., and adjoining territory.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.