Flower:

Dense, branching clusters (panicles) at the tip of the main stem and arising from leaf axils in the upper plant. Flowers are 1/8 inch across, disk-shaped, mostly face down, petal-less with 8 to 20 greenish white to yellow disk flowers clustered in the center with 5 short, thread-like pistils around the outer edge of the disk. 5 broad, hairy and sharply pointed bracts cover the receptacle.

Leaves and stems:

Leaves are 2 to 7½ inches long and 1 to 5½ inches wide, opposite in the lower plant with a few alternately arranged near the flowers, broadly egg-shaped with a pointed tip, long stalked, and typically shallowly 3-lobed. Upper leaves are smaller, more lance-shaped, and typically unlobed. The upper surface is rough textured, the lower silky soft, the leaf edges of young plants often finely toothed becoming coarsely toothed by mid-season. Stems are unbranched except in the flower cluster, hairless in the lower plant but with fine sticky hairs up into the panicle.

Notes:

Few annuals attain the stature of Cyclachaena xanthiifolia, commonly spelled C. xanthifolia (including by MNDNR) and formerly known as Iva xanthifolia. What appear as empty open spaces in the spring can completely fill in with these robust growers by late summer. Of two other similar species that come to mind, Annual Sunflower (Helianthus annua) has a very similar leaves on seedlings and young plants but the leaves stay finely toothed and unlobed throughout the season, and large showy, yellow flowers easily distinguish it later on in the summer. Giant Ragweed (Ambrosia trifida) also produces a similar profile, especially at a distance, but its tri-lobed leaves are more deeply lobed with persistent finely toothed edges and its flower clusters are unbranched. Like Annual Sumpweed (Cyclachaena annua), another midwestern species that does not range into Minnesota, and the ragweeds, Giant Sumpweed produces copius amounts of highly allergenic pollen in late summer as well as causing contact dermatitis in sensitive people.