Butterweed

Packera glabella is common and almost weedy in wet, partially shaded places. The hollow, striated stems of P. glabella are distinctive.

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.

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;

Packera glabella (formerly Senecio glabellus) is one of several plants with the common name butterweed, this one has also been called cressleaf groundsel and yellowtop. It is native to central and southeastern North America. It is toxic when eaten by humans.

Packera glabella involucres