One of the most serious weeds of crop and forest land in the Western United States. Its spread is primarily from creeping root stocks which are distributed by cultivation and gophers. The `snowstorms` of fluff from patches of this species have caused many feuds but actually contain very few viable seeds. This is an extremely variable species, some varieties with entire, spineless leaves. An excellent description of these varieties can be found on page 239 of Ontario Weeds.