Bristly thistle

Cirsium horridulum

''Cirsium horridulum'', called bristly thistle, horrid thistle, yellow thistle or bull thistle, is a North American species of plants in the thistle tribe within the sunflower family. The species is native to the eastern and southern United States from New England to Florida, Texas, and Oklahoma as well as to Mexico, Belize, Guatemala, Honduras, and the Bahamas.

Thomas Nuttall described var. ''megacanthum'' as "one of the most terribly armed plants in the genus."

''Cirsium horridulum'' is a biennial herb up to 250 cm tall, with a large taproot and fleshy side roots that sometimes sprout new shoots. Leaves are up to 40 cm long with thick, sharp spines along the edges. There are usually several flower heads, also with sharp spines, each head with disc florets but no ray florets. Flower color varies from one plant to the next: white, yellow, pink, red or purple.

;Varieties
* ''Cirsium horridulum'' var. ''horridulum'' - from Maine to Guatemala
* ''Cirsium horridulum'' var. ''megacanthum'' D.J.Keil - from the Florida Panhandle to Texas and Oklahoma
* ''Cirsium horridulum'' var. ''vittatum'' R.W.Long - from North Carolina to Louisiana

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