Senecio longilobus,
S. riddellii and
S. spartioides

Common names:
Threadleaf, Riddell, Broom Groundsels
W U.S.
Range land, pasture land, woods
Toxic season:
Leaves are deeply divided, thread-like with smooth margins, up to 3" long. S. longilobus appears grayish because of fine hairs covering leaves. Plants grow from a woody base up to 3' tall. Numerous yellow ray flowers are under 1" across, with yellow or gold centers, growing at branchy stem ends. Fruits include whitish hairy tufts.
Poison type:
Pyrrolizidine alkaloids
Liver damage, rarely resulting in photosensitization. Depression, appetite loss, aimless wandering, discharge from eyes and nose, yellowish mucous membranes, weakness, incoordination, head pressing and nervousness (in horses, AKA "sleepy staggers" or "walking disease"), constipation or bile-stained feces, dry muzzle, prostration, aggression. Signs may occur soon after ingestion of large amount (1-5% of body weight may be lethal for cattle or horses) or damage may take place cumulatively with signs delaying up to 6 months. Fetus and young most susceptible; birth defects possible. Toxins can be passed in milk. Once symptoms appear, liver damage advanced and death likely unavoidable.
Provide supportive treatment. Prognosis poor.
All parts toxic, fresh or dry. Do not allow hungry animals to graze. Cases of poisoning have been reported for all grazing livestock except llamas and alpacas; they also may be susceptible.

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