Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Heads disciform or discoid, the outer fls in our spp. pistillate and fertile, the central ones perfect or sometimes sterile; invol bracts dry, imbricate, at least the inner scarious or with scarious margins; receptacle flat to convex or hemispheric, naked or beset with long hairs; style-branches flattened, truncate, penicillate; achenes ellipsoid or obovoid to nearly prismatic, scarcely compressed, usually glabrous; pappus none; herbs or shrubs, usually aromatic, with alternate, entire to dissected lvs and few to numerous small, ovoid to campanulate or hemispheric heads in a spiciform, racemiform, or paniculiform infl. 100+, N. Hemisphere and S. Amer.
wormwood, sage, mugwort