Subshrubs, 30–100 cm (taproots forming woody crowns). Herbage glabrous. Stems usually multiple (branching upward). Leaves ± evenly distributed (proximal often withering before flowering, pendulous); sessile or obscurely petiolate; blades linear-filiform (or irregularly pinnately divided into linear-filiform lobes), blades or lobes 4–9 cm × 1–5 mm, bases ± linear, ultimate margins entire. Heads 5–20+ in close, corymbiform arrays (involucres campanulate, 7–10 mm diam.). Calyculi usually of 3–8+ lance-linear to filiform bractlets (lengths 1/10–1/3 phyllaries). Phyllaries ± 13, 7–10 (–12+) mm, tips green. Ray-florets ± 8; corolla laminae (often falling early) 8–10 mm. Cypselae hirtellous. 2n = 40.

Phenology: Flowering mostly mid summer–fall, occasionally spring.
Habitat: Sandy or rocky open sites, especially drying, open, flood plains
Elevation: 600–2500 m

Distribution

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• Legacy Map

Ariz., Colo., Kans., Nebr., N.Mex., Okla., S.Dak., Tex., Wyo.

Discussion

Senecio riddellii intergrades morphologically with S. spartioides. Typically, the former has larger heads with campanulate involucres 7–10 mm diam.; the latter has cylindric involucres rarely more than 6 mm diam.

Senecio riddellii is poisonous to livestock. It is now locally scarce because of efforts to eradicate it.

Selected References

None.

Lower Taxa

None.