An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press




THREADLEAF GROUNDSEL-Senecio longilobus Benth.

DESCRIPTION-A half-shrub, forming scraggly bushes, mostly 2 to 6 feet high; reproducing by seeds. The several branched stems are woody below, and become herbaceous at the tops. The leaves, divided into long narrow and threadlike divi- sions, are 1 1/2 to 2 1/2 inches long, arranged alternately on the stems, and are permanently white-woolly hairy. The yellow erect flower heads are bellshaped, about 1/2 inch high and 1 1/2 inch across. There may be several to many in a loose, somewhat flattopped cluster. The outer row of strapshaped flowers, or petallike ray flowers, are about 1/2 inch or more in length, seed-producing, and 8 to 18 in number. The small inner or disk flowers are yellow, numerous, tubular, and are also fertile. The achenes are narrowly cylindrical, about 1/12 inch long, covered with fine, close-pressed whitish hairs, with a tuft of long white hairs at the tip.

DISTRIBUTION-A native shrubby range weed found mostly in the southeastern half of the state, but is distributed throughout the state from Apache to Mohave, south to Cochise, Santa Cruz, and Pima counties; from 2,500 up to 7,500 feet elevation. It occurs on dry, rocky, or gravelly sites on plains, mesas, and along dry flood plains and watercourses. It seldom grows abundantly, but is common and widely distributed. Associated mostly with creosote bush, desert grassland, and pinyon-juniper woodland vegetation, but extending up into the ponderosa pine belt. Also common along roadsides and waste places; flowering in southern Arizona throughout most of the year, but most abundantly from April to November.

POISONOUS PROPERTIES-During most of the year, threadleaf groundsel is unpalatable to domestic livestock. However, it is evergreen, and begins growth earlier in the year than most other range vegetation. At this time, animals are hungry for green forage, and may be attracted to it. Ordinarily, however, they do not eat it, except in dire necessity. The leaves of the new growth are most toxic. Cattle and horses are equally susceptible and the poison may have a cumulative effect. Poisoning is due to the presence of several alkaloids, and death occurs through their toxic effect on the liver. Under normal range conditions, sheep and goats are seldom poisoned by it to the extent of causing death.

Copyright (c) 1972 The Arizona Board of Regents

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