20-120+ cm (taproots forming woody crowns). Herbage
usually glabrous, sometimes sparsely, unevenly hairy. Stems
usually multiple (branching and arching upward). Leaves
evenly distributed (proximal often smaller); sessile or obscurely petiolate; blades narrowly linear to filiform (or parted into linear-filiform lobes), 5-10 cm × 1-6 mm, bases ± linear, ultimate margins entire. Heads
10-20(-60) in compound corymbiform arrays (involucres cylindric or narrowly campanulate, 3-6 mm diam.). Calyculi
0 or of 1-3+ (minute, inconspicuous) bractlets. Phyllaries
usually ± 8, sometimes ± 13, (5-)6-9(-10) mm, tips green or minutely black. Ray florets
± 5 (± 13); corolla laminae 8-12 mm. Cypselae
usually hirtellous, sometimes glabrous. 2n
= 40. Flowering summer-fall. Open, dry disturbed sites, especially stream banks and hillsides; 1000-3500 m; Ariz., Calif., Colo., Nebr., Nev., N.Mex., S.Dak., Tex., Utah, Wyo. Plants with the leaves parted into lobes that are seldom more than 1 mm wide have been recognized as Senecio spartioides
(or as S. multicapitatus
); expression of the character is inconsistent throughout the range and recognition of the two entities is all but impossible to maintain.
Senecio spartioides apparently hybridizes with S. eremophilus in Garfield County, Utah, and perhaps elsewhere (cf., Holmgren, Reveal, and LaFrance 3463 , BRY, KSC, NY). The name Senecio toiyabensis rests upon materials that suggest introgression with S. fremontii. Some specimens usually referred to 41. S. pattersonensis suggest introgression with S. spartioides.