[*] Bracts and equal calyx-teeth awn-tipped, rigid, naked, as long as the corolla; flowers in rather dense mostly terminal heads; leaves rigid, slightly petioled.
1. P. aristàtum, Michx. Minutely hoary-puberulent (1–2° high); leaves ovate-oblong and oblong-lanceolate, acute, sparingly denticulate-serrate (1–2´ long), roundish at the base.—Pine barrens, N. J. to Fla. and La.
Var. hyssopifòlium, Gray. Leaves narrowly oblong or broadly linear, nearly entire and obtuse.—Va. to Fla.
[*][*] Bracts and equal and similar calyx-teeth not awned.
[+] Leaves linear or lanceolate, nearly sessile, entire, very numerous; capitate glomerules small and numerous, densely cymose, imbricated with many short appressed rigid bracts.
2. P. lanceolàtum, Pursh. Smoothish or minutely pubescent (2° high); leaves lanceolate or lance-linear, obtuse at base; heads downy; bracts ovate or lanceolate; calyx-teeth short and triangular.—Dry thickets, Mass. to Dak., south to Ga. and Ark.
3. P. linifòlium, Pursh. Smoother and leaves narrower and heads less downy than in the last; the narrower bracts and lance-awl-shaped calyx-teeth pungently pointed.—Dry ground, Mass. to Minn., south to Fla. and Tex.
[+][+] Leaves lanceolate to ovate, sessile or nearly so, denticulate or entire; heads larger and fewer, with fewer and looser bracts.
4. P. mùticum, Pers. Minutely hoary throughout, or becoming almost smooth, corymbosely much branched (1–2½° high); leaves ovate or broadly ovate-lanceolate, varying to lanceolate, rather rigid, acute, rounded or slightly heart-shaped at base, mostly sessile and minutely sharp-toothed, prominently veined, green when old; the floral ones, short bracts, and triangular or ovate calyx-teeth, hoary with a fine close down; flower-clusters very dense.—Maine to S. Ill., south to Fla. and Ark.
Var. pilòsum, Gray. Hoary with loose pubescence; leaves thinner, oblong-lanceolate, mostly acute or acutish at base; bracts and especially the narrower (often somewhat unequal) calyx-teeth often villous-pubescent. (P. pilosum, Nutt.)—Ohio to Iowa, Kan., and Ark.