Submodule 5: Most Common Western Rangelands Weeds

Musk Thistle

Musk thistle (Carduus nutans) is a biennial forb that forms a rosette after germination. This rosette has leaves with a prominent mid-vein that can grow up to 10 inches (25 cm) long and 4 inches (10 cm) wide, with the entire plant being up to 2 feet (0.6 m) in diameter. After bolting, musk thistle may have 1 to 7 branched stems that grow 2 to 8 feet (0.6-1.8 m) in height; these stems have spiny wings protruding from the stem almost to the top of the plant. Stem leaves are 3 to 6 inches (7.6-15.2 cm) in length and spiny. Large composite flowers (1.5 to 3 inches or 3.8-7.6 cm in diameter) are solitary and found at the end of shoots. Spine-tipped bracts that look like a pinecone surround these flowers.

(photo courtesy Larry Howery)