101. Packera Á. Löve & D. Löve (ragwort)

Plants annual, biennial, or perennial, sometimes with rhizomes or stolons. Stems erect or strongly ascending, usually unbranched below the inflorescence, sometimes lined or angled, glabrous or with tangled or woolly (cobwebby) hairs. Leaves in a basal rosette (this sometimes absent at flowering) and alternate, progressively reduced in size from the stem base to tip, glabrous or with tangled or woolly (cobwebby) hairs, sessile or the lowermost short- to often long-petiolate, the bases weakly to strongly clasping the stem. Leaf blades unlobed to weakly or strongly pinnately lobed, less commonly pinnately compound, the terminal lobe or leaflet then usually larger than the lateral ones, the margins otherwise toothed or scalloped to nearly entire, the venation pinnate, the undersurface often dark purple. Inflorescences terminal and axillary from the uppermost leaves, panicles consisting of loose clusters to less commonly solitary heads at the branch tips, broadly rounded to more or less flat-topped in profile. Heads radiate (discoid elsewhere), short- to long-stalked, with numerous florets. Involucre cylindrical to slightly wedge-shaped or somewhat hemispherical, the bracts in 2 series, glabrous (cobwebby-hairy in P. tomentosa), those of the inner series 13–21, more or less flat dorsally, those of the outer series usually 3–7 (sometimes obscured by hairs in P. tomentosa) minute, ascending and usually incurved. Ray florets mostly 8–13, the corolla bright yellow, the lobe usually minutely 3-toothed at the tip. Disc corollas 4.5–7.0 mm long (including the lobes), bright yellow. Style branches with a stigmatic line along each inner margin. Fruits narrowly oblong to narrowly oblong-elliptic in outline, not flattened, 5–10-ribbed, minutely hairy or glabrous, brown to dark brown. About 60 species, North America, Asia.

A number of authors have noted the problems of delimiting species in this group and noted how, in some portions of their ranges, individual species can be difficult to determine with confidence. In Missouri, the main problem appears to be in distinguishing P. paupercula from P. plattensis, although specimens of P. aurea, P. obovata, and P. pseudaurea also are sometimes misdetermined in herbaria. Steyermark (1963) recommended that basal leaves and rootstocks should be collected to facilitate identification of species.

Barkley (1962, 1978) stated that putative hybrids tend to occur at sites where two or more species of Packera grow together. He also suggested that the changing climate at the close of the Pleistocene ice age brought together taxa that formerly were relatively isolated geographically. Various experts over the years have annotated Missouri specimens representing the following putative hybrids: P. aurea × obovata, P. aurea × paupercula, P. obovata × paupercula, and P. obovata × plattensis. Other hybrid combinations are to be expected, but they may be difficult to detect morphologically, for example P. paupercula × plattensis.