Flower:

Tight clusters of a few to several short-stalked flowers at the top of the stem and arising from leaf axils in the upper plant. Flowers have 9 to 25+ pinkish rays (petals) that have a few teeth at the tip; when fully open the flower is more bell-shaped, ~½ inch diameter. The styles are longer than the rays and have divided, curled tips.

Surrounding the base of the flower, forming a tube, are 2 sets of bracts. The outer bracts are short, triangular and dark green or purple; the inner bracts are green to purple, lance-elliptic, blunt to pointed at the tip and up to ½ inch (10 to 12 mm) long. Bracts, flower stalks and the upper stem are all moderately to densely covered in long white hairs.

Leaves and stems:

Leaves are alternate, the lowest leaves largest, up to 10 inches (24+ cm) long and 4 inches (10 cm) wide, generally elliptic to somewhat spatula-shaped, usually broadest above the middle, rounded to pointed at the tip, tapering at the base to a winged stalk. Lower leaves usually persist through flowering. Surfaces are hairless and smooth, edges are toothless or irregularly toothed. Color is green to blue-green.

Leaves become smaller, more oblong-elliptic, stalkless and clasping as they ascend the stem, reduced to bracts in the flower clusters. Stems are single, erect, unbranched, green to purple or purple spotted, often with a waxy bloom (glaucous), and hairless below the flower clusters.

Fruit:

Fruit is a golden brown seed 5 to 6 mm long, linear to elliptic, with a tuft of pale yellow or light brown hairs to carry it off in the wind.

Notes:

Purple Rattlesnake-root, a.k.a. Prenanthes racemosa, is primarily found in sunny, moist, grassy areas in late summer but can tolerate drier conditions. It is common to see single plants widely scattered, but in the right conditions you may come across a loose cluster of plants. It's easy to distinguish from other Nabalus species by the pinkish flowers with hairy, (usually) purple bracts, clasping mid-stem leaves, and stem hairs only in the flower clusters, smooth below. The flower cluster can appear spike-like but is made up of small racemes or panicles in the leaf axils.

Most similar is Rough Rattlesnake-root (Nabalus asper), an uncommon species of dry prairies, which has pale yellow flowers, rough-textured leaves and stems, leaves are not clasping, and the lower leaves wither away by flowering time. The other two related species in Minnesota are White Rattlesnake-root (N. albus) and Nodding Rattlesnake-root (N. crepidineus), both of which are (usually) taller plants, have larger branching clusters of flowers and more variable shaped leaves; N. albus is the only one of this group that has hairless floral bracts..

Note the genus has gone back and forth between Nabalus and Prenanthes; since 2010 Nabalus has more often been the accepted genus.