Cirsium arizonicum

Cirsium arizonicum
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Asterales
Family:	Asteraceae
Tribe:	Cynareae
Genus:	Cirsium
Species:	C. arizonicum
Binomial name
Cirsium arizonicum (A.Gray) Petr.

Cirsium arizonicum (Arizona Thistle) is a species of thistle in the genus Cirsium, native to the southwestern United States, including Arizona, southeastern California, New Mexico, Nevada, and Utah.^[1][2][3]

It 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 inflorescences 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.^[1][2]

Five varieties have been identified:^[1]

• Cirsium arizonicum var. arizonicum (syn. var. nidulum (M.E.Jones) S.L.Welsh)
• Cirsium arizonicum var. bipinnatum (Eastwood) D.J.Keil. Four Corners Thistle.
• Cirsium arizonicum var. chellyense (R.J.Moore & Frankton) D.J.Keil (syn. C. chellyense R.J.Moore & Frankton). Navajo Thistle.
• Cirsium arizonicum var. rothrockii (A.Gray) D.J.Keil (syn. C. rothrockii (A.Gray) Petrak). Rothrock's Thistle.
• Cirsium arizonicum var. tenuisectum D.J.Keil. Desert Mountains Thistle.

References

1. ^ ^{a b c} Flora of North America: Cirsium arizonicum
2. ^ ^{a b} Jepson Flora: Cirsium arizonicum
3. ^ USDA Plants Profile: Cirsium arizonicum