This weed is widespread in northeastern states and adjacent Canada. Species of Pilosella "belong to a huge polyploid-apomictic complex without clear specific boundaries" (Cr); 2n = 18, 27... 72. All are disturbance-adapted perennials with rosettes of basal leaves produced at ends of rhizomes or stolons. Some other European species of Pilosella have been reported, but not verified: P. piloselloides (Vill.) Sojak (BA), which differs from caespitosa in its less hairy, glaucous leaves; P. aurantiaca (L.) F. Schultz & Schultz-Bipontinus (Faller 1975), an ornamental plant with reddish-orange flowers; and P. officinarum F. Schultz & Schultz-Bipontinus (Faller 1975), which has solitary heads. Like caespitosa, these species are widely scattered in North America, and are expected in Ky. A spreading patch of P. flagellaris (Willd.) P.D. Sell & C. West was noted in 2014 at the entrance to Dropseed Nursery in OLDH; further investigation is needed. Stems of this species have relatively long hairs (up to 2-4 mm), stipitate-glandular hairs, and short stellate hairs; there are usually just 2-5 heads.