Threetooth ragwort

Senecio tridenticulatus Rydberg, Bull. Torrey Bot. Club 27: 175, plate 5, fig. 12. 1900; S. acutidens Rydberg; S. compactus (A. Gray) Rydberg 1894, not Kirk 1880; S. densus Greene; S. oblanceolatus Rydberg

Perennials, 10–30+ cm; taprooted (caudices ascending to erect). Stems 1 or multiple, clustered, usually glabrous, rarely sparsely floccose-tomentose, leaf axils sometimes tomentose. Basal leaves (and proximal cauline, relatively thick and turgid) petiolate; blades lanceolate or narrowly oblanceolate, 20–40+ × 5–15 mm, bases tapering, margins usually entire, sometimes sub-pinnatisect (apices subentire or dentate). Cauline leaves gradually reduced (± petiolate or sessile). Heads 4–15+ in corymbiform arrays. Peduncles bracteate, glabrous or sparsely tomentose. Calyculi incon-spicuous. Phyllaries 13 or 21, green, 6–10 mm, sparsely tomentose proximally, glabrous distally. Ray florets 8–10(–13); corolla laminae 5–8+ mm. Disc florets 45–60+; corolla tubes 3–3.5 mm, limbs 4–5 mm. Cypselae 1.5–2.5 mm, glabrous or sparsely hirtellous on ribs; pappi 5–6 mm. 2n = 46.

Flowering late May–early Jul. Open, dry areas, roadsides, gravelly or sandy slopes, short-grass prairies or sagebrush scrubs; 1000–2000 m; Colo., Kans., Nebr., N.Mex., N.Dak., Okla., S.Dak., Tex., Wyo.

Packera tridenticulata is found throughout the central High Plains, in the foothills of the Rocky Mountains, and in high valleys to the west of the Rocky Mountain front. It tends to grow in clumps; the multiple stems arise from well-developed taproots. It apparently hybridizes with P. neomexicana var. mutabilis where their ranges overlap.