Cirsium arizonicum

Cirsium arizonicum, the Arizona thistle, is a North American species of thistle in the sunflower family, native to the southwestern United States and northwestern Mexico. It has been found in Arizona, southeastern California, New Mexico, Nevada, Colorado, Utah, Sonora, and northwestern Chihuahua.[2][3][4][5][6]

Cirsium arizonicum
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Asterales
Family:	Asteraceae
Genus:	Cirsium
Species:	C. arizonicum
Binomial name
Cirsium arizonicum (A.Gray) Petr.
Synonyms[1]
Synonymy Carduus arizonicus (A.Gray) Greene Carduus nidulus (M.E.Jones) A.Heller Cirsium nidulum (M.E.Jones) Petr. Cnicus arizonicus A.Gray Cnicus nidulus M.E.Jones Cirsium effusum (Maxim.) Matsum. Cnicus effusus Maxim. Cirsium chellyense R.J.Moore & Frankton Cirsium chuskaense R.J.Moore & Frankton Cirsium navajoense R.J.Moore & Frankton Carduus rothrockii (A.Gray) Greene Cirsium rothrockii (A.Gray) Petr. Cnicus rothrockii A.Gray

Cirsium arizonicum is a herbaceous plant that can be either biennial or perennial, reaching 30–150 cm in height. The spiny leaves are oblong-obovate with pinate lobes; the basal leaves are larger, 10–40 cm long, while leaves on the upper stem can be only 3 cm long. The inflorescence is 3–4 cm in length and 1.5–2 cm diameter, red to pink or purple, with all the florets of similar form (no division into disc and ray florets); individual plants are very variable in the number of heads produced, from one to 100. Flowering is from mid spring to mid fall. The species occurs in mountains, at elevations of 900–3,600 m.[2][3][7]

Five varieties have been identified:[2]

• Cirsium arizonicum var. arizonicum (syn. var. nidulum (M.E.Jones) S.L.Welsh) - Arizona, New Mexico, California, Nevada, Utah, Sonora, Chihuahua
• Cirsium arizonicum var. bipinnatum (Eastwood) D.J.Keil. Four Corners thistle - Arizona, New Mexico, Colorado, Utah, Sonora
• Cirsium arizonicum var. chellyense (R.J.Moore & Frankton) D.J.Keil (syn. C. chellyense R.J.Moore & Frankton) Navajo thistle - Arizona, New Mexico
• Cirsium arizonicum var. rothrockii (A.Gray) D.J.Keil (syn. C. rothrockii (A.Gray) Petrak). Rothrock's thistle - Arizona, New Mexico, Sonora; this variety is found on both rims of the Grand Canyon and for a short distance below.[8]
• Cirsium arizonicum var. tenuisectum D.J.Keil. Desert mountains thistle - California, Nevada, Sonora