The flowerheads sit individually in the leaf axils or on a peduncle. These heads are subtended by 2 rows of free involucral bracts, the outer 3–5 are protruding, triangular in shape, broadest and leaflike, the inner lance-shaped, ascending and may be spiny. Each head consists of a whorl of yellow, infertile ray florets with 4 teeth at their tips, surrounding yellow disc florets that each have five long, free lobes. Adjacent each of the outer involucral bracts, several florets are fertile, and the surrounding parts of the common base of all florets in the head (or receptacle) swell and eventually become woody. The receptacle breaks up at maturity, each section corresponding with one of the persistent outer bracts. These segments break free from the parent plant and act as the dispersal units. The ribbed, flask-shaped, more or less curved fruitlets germinate inside the protective encasement of the woody segments. These are topped by a pappus of winged scales that have merged at their base. "D. spinosa" lacks milk sap, has hairless, more or less oval leaves with spines that often enclose the stem at base, and the swollen, eventually woody segments of the receptacle containing the fruitlets lack spines. "D. carnosa" has milk sap, elliptic to linear, variably tomentose leaves, and the swollen and eventually woody segments of the receptacle containing the fruitlets are spiny. Two varieties are distinguished. "D. carnosa" var. "carnosa" is hairless or becomes hairless with age, while "D. carnosa" var. "tomentosa" remains densely felty hairy at least on the undersides of the leaves. "Cuspidia cernua" has bristle-like pappus on top of the fruitlets and the fruiting head remains intact, while both "Didelta"-species have chaffy pappus and the fruiting head breaks into several triangular segments when ripe. The first to describe species that are nowadays included in the genus "Didelta" was Carl Linnaeus the Younger in 1781 and he named them "Polymnia carnosa" and "Polymnia spinosa". The type species of that genus is "Polymnia canadensis", named by his father Carl Linnaeus in 1758.