Possibly derived from the mythological Helenus, son of King Priam of Troy.
Annual or perennial herbs, glabrous to hairy. Stems erect, simple or branched. Leaves along stems, alternate, margins entire to lobed, often decurrent as wings on stems. Capitula radiate or diskoid, terminal, solitary or in loose corymbs, with stalks. Involucral bracts in 1-3 rows, overlapping, unequal, spreading or curved backwards. Receptacle convex to nearly spherical. Ray florets female or sterile, usually ligulate, yellow or purplish brown. Disk florets bisexual, tubular, yellow or purplish brown. Achenes obpyramidal, 4- or 5-angled, usually ribbed. Pappus of about 5 scales with a terminal bristle.
Leaf bases decurrent as wings along stems; pappus of about 5 scales, each with a terminal bristle.
About 40 species from N, C and S America.
Source: (2002). Dahlia. In: . Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.