Plants 30-80 cm. Stems erect to ascending-erect (not sprawling-scandent). Leaves: petioles 0.5-3 cm; blades deltate-ovate, 1.5-5 × 0.6-2 cm, bases broadly cuneate to subtruncate, margins irreg-ularly crenate-serrate, apices acute to acuminate. Involucres (4-)5-6 mm. Phyllaries: ovate (outer) or elliptic (inner), glabrous, apices usually obtuse to rounded, rarely truncate. Corollas usually pale purple, rarely white. Cypselae 1-1.2(-1.5) mm, glabrous or glabrate. Flowering Sep-Dec. Rich soils, along streams, rocky slopes; 800-1500 m; Ariz., N.Mex.; Mexico. Fleischmannia sonorae was reported for Arizona by T. H. Kearney and R. H. Peebles (1960) and F. Shreve and I. L. Wiggins (1964) as Eupatorium pycnocephalum Lessing [= Fleischmannia pycnocephala (Lessing) R. M. King & H. Robinson)]; revised concepts of this species group (B. L. Turner 1996+, vol. 2) place F. pycnocephala as a related species in Mexico and Central America, not reaching northwestward to Arizona.