Annuals or biennials, 20-70+ cm; fibrous-rooted (caudices relatively short, weak). Stems 1 (striated, frequently hollow, often pink- to purple-tinged), glabrous or leaf axils sparsely tomentose. Basal leaves (and proximal cauline) obscurely petiolate; blades obovate to oblanceolate, sometimes lyrate (lateral lobes to 5 pairs, terminal lobes larger than laterals), 50-150+ × 10-30+ mm, bases tapering, ultimate margins crenate to irregularly undulate. Cauline leaves gradually reduced (weakly clasping, similar to basal). Heads 8-30+ in umbelliform or cymiform arrays (robust plants with multiple arrays). Peduncles bracteate, glabrous or bases tomentose. Calyculi conspicuous (bractlets 2.5-4 mm). Phyllaries (13-)21, green, 5-7 mm, glabrous. Ray florets (8-)13; corolla laminae 7-9 mm. Disc florets 35-50+; corolla tubes 2.5-3.5 mm, limbs 2-3 mm. Cypselae 1-1.5 mm, sparsely hirtellous on ribs or glabrous; pappi 3-4 mm. 2n = 46. Flowering (Feb-)mid Mar-late May. Open wet areas, edges of woodlands, stream banks, roadsides, meadows, marshes, fallow fields; 0-600 m; Ala., Ark., Fla., Ga., Ill., Ind., Kans., Ky., La., Miss., Mo., Nebr., N.C., Ohio, Okla., S.C., Tenn., Tex. Packera glabella is common and almost weedy in wet, partially shaded places. The hollow, striated stems of P. glabella are distinctive.
From Flora of Indiana (1940) by Charles C. Deam
This plant was not known to Schneck in 1876 in the Lower Wabash Valley, and in 1897 Blatchley reported it as scarce in Vigo County, but it was collected by Clapp in 1838 at New Albany. Evidently it is migrating into the state at a rapid pace. It is now a common to abundant weed in most of the area shown on the map. It prefers cultivated and fallow ground. In the springtime, fields not plowed, oatfields, and wheatfields are sometimes yellow with it.
Fibrous-rooted, mostly single-stemmed annual or winter- annual 1.5-8 dm, glabrous or obscurely floccose-tomentose in the axils; lvs mostly once pinnatifid (or in part twice pinnatifid) with generally rounded teeth and lobes, or the basal sometimes merely round- toothed, the largest ones at or near the base of the stem, to 20 נ7 cm, progressively reduced upward; heads ±numerous, the disk 5-10 mm wide; invol 4-6 mm, its bracts ca 21 or 13; rays 5-12 mm; achenes minutely hairy or glabrous; 2n=46. Moist, open or shaded places, often a weed in low fields; N.C. and Ky. to Fla., w. to S.D. and Tex., and adventive n. to s. Ont. May-July.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.