Acevedo-Rodríguez, Pedro & collaborators. 1996. Flora of St. John, U.S. Virgin Islands. Mem. New York Bot. Gard. 78: 1-581.
Genus Description - Perennial herbs, less commonly annuals, biennials, or shrubs; stems glabrous to pilose. Leaves simple, alternate, or rarely all basal (in ours), sessile or short-petiolate; blades entire to variously toothed or divided, pinnately veined. Inflorescence monocephalous, or few-headed and cymose, corymbiform, or paniculate. Heads radiate or rarely disciform, generally borne on leafless peduncles; involucre bell-shaped to hemispheric; involucral bracts subequal or 2(-5)-seriate, linear to lanceolate; receptacle flat or slightly convex, naked. Ray flowers nearly always present, pistillate, many, usually in 2 series, the limbs long, narrow. Disk flowers bisexual, numerous; corollas shortly 5-lobed, tubular to bell-shaped; style branches dorsally papillose, short. Achenes mostly compressed, the sides commonly strongly and thickly 1-nerved, the faces also sometimes variously ribbed; pappus of several to many fragile capillary bristles about as long as the disk corollas, sometimes an outer series of shorter bristles or scales or an outer crown-shaped pappus also present.
Distribution and Ecology - A genus of about 200 species of worldwide distribution, but more commonly found in temperate zones.