This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Circium ochrocentum, Gray (Carduus ochrocentrus, Greene)
Native. Biennial. Propagates by seeds.
Time of bloom: May to September.
Seed-time: July to October.
Range: Nebraska to Nevada, Arizona, and Texas.
Habitat: Plains and prairies.
Fig. 355. - Pasture or Fragrant Thistle (Circium pumilum). X 1/4.
2l Stem two to six feet tall, stout, densely white-woolly, leafy to the top. Leaves oblong lance-shaped in outline but deeply pin-natifid into triangular or lance-shaped segments, armed with long, stiff, yellow spines, white-woolly on the under side, sessile or slightly clasping, the lowest with short, margined petioles. Heads solitary, terminal, about two inches broad, the outer bracts of the involucre lance-shaped and tipped with stout, yellow spines about as long as themselves, the inner ones long-pointed but unarmed; flowers light purple.
Another Thistle of the plains, much resembling this one in its dense white-woolliness but smaller and less fiercely armed, is the Wavy-leaved Thistle (Circium undulatum, Spreng), which has a wider range, extending to the Northwest Territory.
Means of control the same as for C. lanceolatum.