Sonoran slender-thoroughwort

Eupatorium sonorae A. Gray, Smithsonian Contr. Knowl. 5(6): 74. 1853

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.