Cirsium clavatum var americanum

Cirsium clavatum is a biennial or perennial herb up to 3 feet (100 cm) tall, blooming only once before dying. It is a polymorphic and variable species. Leaves have thin spines along the edge, much smaller than those of related species. There are several to many flower heads, with white or pale pink disc florets but no ray florets. It occurs in the Southern Rocky Mountain region of Wyoming, Colorado and New Mexico. While Bigelow’s tansyaster is very similar to the hoary tansyaster, it is much more restricted to habitat and range.