Butterweed

Senecio glabellus Poiret in J. Lamarck et al., Encycl. 7: 102. 1806; S. carolinianus Sprengel; S. densiflorus M. Martens; S. lobatus Persoon; S. lyratus Michaux 1803, not Linnaeus f. 1782; S. mississipianus de Candolle;

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.