Flower:

Up to 200 small daisy-like flowers in an open branching cluster at the top of the plant. Flowers are ½ to ¾ inch across with 50 to 100 short, narrow white rays (petals) that may sometimes be pink or bluish tinged, and yellow center disk. Occasionally flowers have very short or nearly no rays. Early heads form at the tip of the branch and nearby lateral buds, later heads emerge from lower leaf axils creating an open array of white blooms.

Behind the flower are 2 to 4 rows of narrow light green bracts that are hairless or sparsely hairy. The flower stalk is ¾ to 1 inch long and also hairless or sparsely hairy.

Leaves and stems:

Leaves are 1 to 6 inches long, ¼ to 1 inch wide, mostly toothless or with a few small teeth, hairless to sparsely hairy, becoming smaller as they ascend the stem.

Leaves near the base are elliptic, spatula-shaped to rounded, tapering to a slender stalk, becoming stalkless and more lance-oblong or linear farther up the stem. Stems are multiple from the base, stiff and hairless to sparsely hairy.

Fruit:

Fruit is a small head of nondescript brown seed, each about 1mm long, with a few relatively short light brown hairs attached.

Notes:

Prairie Fleabane is one of the more common Erigeron species in Minnesota, distinguished by the (usually) numerous small (¾ inch or less diameter) white daisy-like flowers with up to 100 very narrow rays, hairless to sparsely hairy leaves and stems, spoon or spatula-shaped basal leaves, narrowly lance-elliptic and toothless stem leaves that are stalkless but not clasping. Of the other Erigeron species, Philadelphia fleabane, (Erigeron philadelphicus) stem leaves are toothed and clasping, flowers bloom earlier, and is more a woodland species. Annual Fleabane (Erigeron annuus) has broader, more distinctly toothed leaves, is hairier overall, and tends to be a taller plant. Smooth Fleabane (Erigeron glabellus) and Robin's Plantain (Erigeron pulchellus) both are overall hairier, have few-flowered clusters of larger flowers (over ¾ inch diameter) with rays that are violet to pinkish or white, and perennial where Prairie Fleabane is usually an annual or sometimes a biennial.

There are 2 recognized varieties of E. strigosus in Minnesota: var. septentrionalis is uncommon, characterized by flattened (in cross section) appressed to spreading hairs about 1mm long on the stems and flower bracts; var. strigosus is the more common, with round (in cross section) hairs that are appressed to ascending, up to .5mm long, and more sparse. The other two vars have a limited range in the southeastern US and are usually perennial.