Canada Thistle, Creeping Thistle: Cirsium arvense (Synonyms: Cirsium arvense var. arvense, Cirsium arvense var. horridum, Cirsium arvense var. mite) -
Clustered Thistle, Short-styled Thistle: Cirsium brevistylum -
Mountain Thistle, Fringe-bract Thistle: Cirsium remotifolium var. odontolepis (Synonyms: Cirsium callilepis, Cirsium callilepis var. callilepis, Cirsium callilepis var. oregonense, Cirsium centaureae, Cirsium remotifolium ssp. oregonense, Cirsium remotifolium ssp. pseudocarlinoides) -
Wavy-leaf Thistle: Cirsium undulatum (Synonym: Cirsium undulatum var. undulatum) - Wavy-leaf Thistle is a stout, single-stemmed short-lived perennial. The stem may be branched above, and stems range from 30-120 cm tall. All surfaces of the stem and leaves are persistently white-woolly haired, although the upper leaf surfaces may be less covered, and occasionally may be glabrous. The stems, leaves and flower heads are covered with sharp spines.
Bull Thistle, Common Thistle: Cirsium vulgare (Synonym: Carduus vulgare) -