• Cirsium horridulum, called bristly thistle, purple thistle, or yellow thistle is a North American species of plants in the tribe Cardueae within the family Asteraceae. (wikipedia.org)
  • 24(12): 423-428, 590 Nuttall quoted in Flora of North America, Bigspine thistle, Cirsium horridulum Michaux var. (wikipedia.org)
  • Transactions of the American Philosophical Society, new series 7: 421 as Cirsium megacanthum Flora of North America, Bristly or horrid or yellow or bull thistle, Cirsium horridulum Michaux, Fl. (wikipedia.org)
  • Cirsium horridulum Michaux var. (floraofalabama.org)