Plants 100-300 cm. Stems ridged to angulate (usually glabrous, rarely sparsely puberulent distally, not glaucous). Basal leaves: (petioles to 30 cm) blades (with 3-5 main veins) reniform or ovate-cordate, to 40+ cm, margins lobed or dentate. Cauline leaves: proximal petiolate, blades ovate, margins entire, serrate, or dentate; distal petiolate or sessile, smaller (rarely hairy). Involucres (8-)10-13(-14) mm. Phyllaries pale green, narrowly ovate, midveins not winged (tips obtuse). Corollas white or greenish, 8-9(-10.5) mm. Cypselae fusiform or clavate, 4-5 mm (dark brown or purple, 4-5-ribbed); pappi 6-8 mm. 2n = 50.
Arnoglossum muehlenbergii of H. Robinson, Cacalia muhlenbergii of Fernald, and Mesadenia muhlenbergii of Rydberg were based on Senecio muehlenbergii Schultz-Bipontinus, a superfluous name based on Cacalia reniformis Muhlenberg ex Willdenow.
Stout, fibrous-rooted, glabrous perennial 1-3 m; stem conspicuously 6-8-angled and sulcate; lvs green on both sides, irregularly dentate and sometimes shallowly lobed, commonly ±ciliolate in the sinuses, palmately veined, the lower very large and long-petioled, to 8 dm wide, often reniform, the upper reduced and more flabellate or ovate; heads numerous in a short and broad, flat-topped infl, 5-fld, narrowly cylindric, the disk 3-7 mm wide as pressed; invol 7-12 mm, its principal bracts 5, sometimes with a few minute basal bracteoles; receptacle with a short conic projection in the center; 2n=50. Open woods; N.J. and Pa. to Minn. and Mo., s. to Ga. and Miss. June-Sept. (C. reniformis; Mesadenia r.; M. muehlenbergii)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Infrequent to local in the southern two thirds of the state. It prefers the moist, rich soil of beech slopes but it is found also in other types of moist soil, even in springy places. Ordinarily only a few plants are found at a place, but in 1921 I was asked by a land owner, who lived about five miles southeast of Greensburg, Decatur County, to identify an obnoxious weed which he had in his woods on an open beech ridge and which proved to be a vigorous growth of this species in almost a pure stand over an acre or more.