Silphium perfoliatum
Family: Asteraceae
cup-plant
Silphium perfoliatum image
Merel R. Black  
Etymology: Silphium: old Greek generic name referring to resinous juice
Plants: erect, perennial, 3'-8' tall forb; stems square in X-section, mostly smooth
Leaves: opposite, strongly toothed, upper and lower leaves about the same size, surrounding the stem to form a cup
Flowers: head 1 3/4"- 2 3/4" wide with 16-35 (usually 21 or 34) yellow rays 1/2"-1 1/2" long, disk 1/2"-1" wide; inflorescence of several heads in an open, branched cluster; blooms July-Sept.
Fruits: dry seed with no fluffy pappus
Habitat: full to partial sun; wet to moderate moisture; prairies, woods, streambanks; in sandy, loamy soil
Conservation Status: Native