Musk, or nodding thistle is an aggressive, biennial herb with showy red-purple flowers and painful spiny stems and leaves. Populations in North America exhibit almost continuous variation in characteristics such as hairiness, leaf size, spine length, flower stalk diameter, width and shape of bracts, and corolla length. In general, mature plants range in height from 1.5 to 6 feet tall, and have multi-branched spiny stems. Leaves are dark green, coarsely bipinnately lobed, with a smooth waxy surface and a yellowish to white spine at the tip. The large disk-shaped flower heads, containing hundreds of tiny individual flowers, are 1.5 to 3.5 inches in length and occur at the tips of stems. Phyllaries are spine-tipped and overlap with several rows. Flower heads will droop to a 90-degree angle from the stem when mature, hence its alternate name, nodding thistle. Each plant may produce thousands of straw-colored seeds adorned with plume-like bristles.
Seeds and seedhead (L) and flowerhead (R).