Threadleaf groundsel is a typical representative of the relatively 

 few shrubby species of this largely herbaceous genus which belongs 

 to the aster family (Asteraceae, or Compositae). The generic name 

 is from the Latin senex, an old man, and alludes to the hoary herb- 

 age of certain of the Old World species. The specific name 

 longilobus and the common name threadleaf refer to the very slen- 

 der, deeply cut lobes of the leaves. This species ranges from western 

 Texas to Colorado, Utah, Arizona, and south into Mexico. It seldom 

 grows abundantly, but is common and widely distributed from the 

 creosotebush and mesquite types up through the woodland (oak 

 and pinon-juniper types) into the ponderosa pine belt. It is most 

 common on dry open ridges, mesas, and parks throughout the pinon- 

 juniper woodland belt and is not uncommon along roadsides and 

 other waste places. Although occurring on a wide variety of soils, 

 from rocky or sandy to adobe clay, it apparently prefers sandy or 

 gravelly loams. It is drought-resistant by virtue of its deep root 

 system, hoary pubescence, and other xeropnytic adaptations. 



Threadleaf groundsel, like other shrubby species of Senecio, is 

 much inferior to several of the herbaceous species and has little or 

 no forage value. It is eaten slightly by goats and, in cases of dire 

 necessity, sheep will graze the foliage. Recent investigations by 

 Clawson * have demonstrated that this species (and especially its 

 young leaves) is poisonous to cattle and horses and, to a lesser ex- 

 tent, to sheep. Mr. Clawson thinks that under range conditions 

 this plant "may, and probably does, cause losses of livestock at 

 times." However, in view of its normally very low palatability, 

 threadleaf groundsel is probably not a source of danger on the range 

 except where serious range depletion obtains, as in periods of pro- 

 longed drought or on badly overgrazed or overstocked areas. 



Threadleaf groundsel is usually a half shrub ; the stems are largely 

 herbaceous, except at the base, in its northern range, but are often 

 woody, except for the tops, in its southern range. The plant is vari- 

 able in the form of its leaves and in the hairiness of both its leaves 

 and stems. In some specimens, nearly all leaves are entire ; in others, 

 they are dissected to the midrib into narrow lobes. Some individuals, 

 especially those growing at the higher elevations, are only slightly 

 soft-hairy, but those growing on the foothills and mesas are com- 

 monly densely covered with soft fine hairs. The yellow flowers are 

 among the first to appear in the spring, and usually bloom all sum- 

 mer ; southward they sometimes bloom throughout most of the year. 



Broom groundsel (S. spartioi' des) is another common half shrub 

 of this genus. This species is similar to threadleaf groundsel, with 

 the exception that it is hairless and its leaves are entire or rarely 

 lobed at the base. It ranges from Nebraska and Wyoming south- 

 ward to Arizona and Texas, and grows on dry, open ridges in the 

 sagebrush, oak and pinon-juniper woodlands, and ponderosa-pine 

 belts. The plant is seldom touched by livestock unless other feed 

 is scanty or absent. Preliminary studies by Clawson (op. tit.) have 

 demonstrated that it contains toxic properties. (See W16S.) 



1 Clawson, A. B. THE AMERICAN GROUNDSELS SPECIES OF SENECIO AS STOCK POISONING 

 PLANTS. Vet. Med. 28 (3) : 105-110, illus. 1933. 



