The label "aster" has been applied as the common name to species in what are now known to be in a dozen or more distinct genera within the tribe Astereae of the Sunflower Family. Asters are herbaceous perennials. Like the "flower" of a sunflower, aster "flowers" are really groups of flowers called heads made up of a basket of small leaves surrounding two kinds of small flowers (florets). The pappus of the North American Clade of the Astereae has four distinct series of bristles in more basal genera, e.g. Doellingeria. More derived genera have three, two or one distinct series of bristles.