[Ageratum corymbosum f. albiflorum B. L. Rob., moreAgeratum corymbosum f. euryphyllum (B. L. Rob.) M. F. Johnson, Ageratum corymbosum f. salicifolium (Hemsl.) M. F. Johnson, Ageratum corymbosum subsp. elachycarpum (B. L. Rob.) M. F. Johnson, Ageratum corymbosum var. jaliscense , Ageratum corymbosum var. lactiflorum B. L. Rob., Ageratum elachycarpum B. L. Rob., Ageratum guatemalense M.F. Johnson, Eupatorium coeruleum Sessé & Moc.]
Perennials or subshrubs, 30-100 cm (fibrous-rooted). Stems erect to basally decumbent, puberulent to minutely strigoso-hispid. Leaf blades ovate to rhombic-lanceolate, 3-8 × 1-3.5 cm, margins toothed, abaxial faces usually puberulent, sometimes minutely strigoso-hispid, densely gland-dotted. Peduncles finely puberulent (not pilose), eglandular. Involucres 5-6 mm. Phyllaries narrowly lanceolate (0.4-0.7 mm wide, innermost often 1-1.5 mm longer than outer), finely puberulent, eglandular, tips green or purplish, filiform. Corollas usually blue to lavender, sometimes white. Cypselae glabrous; pappi usually crowns of connate scales with erose margins or tubular portions longer than divisions, rarely with 1 or more awnlike lobes. 2n = 20, 30, 40.
Flowering Jul-Oct. Crevices, ledges, cliffs, other rocky sites in canyons, along streams, in desert grasslands, oak-agave, oak, oak-juniper, and pine-oak woodlands; (900-)1200-1900 m; Ariz., N.Mex.; Mexico.