Musk Thistle (Nodding Thistle)

Family: 
Asteraceae (sunflowers)
Description: 

Musk thistle is a large, spiny biennial with rose-purple flower heads up to 2½ inches wide. The stems are commonly winged with spiny leaf tissue. The plant forms basal rosettes during its first year, which have deeply lobed leaves that are up to 10 inches long and 4 inches wide, and have a prominent, nearly white center vein. During the second year, an upright flowering stalk grows that has smaller, very spiny leaves. The flower heads are mostly solitary and nod at the branch tips. At the base of each flower head are numerous, spine-tipped bracts, 1/8 to 3/8 inch wide, that curve away from the heads. Blooms June through October. A single plant can produce 11,000 seeds, spread by silky parachutes.

Similar species: Our native thistles have strongly whitened undersides to the leaves, whereas this thistle (and other exotic thistles) has both sides of the leaves the same color.

Size: 
Height: to 6 feet.
Habitat and conservation: 
Musk thistle is found in waste ground, old fields and pasture and along roads and railroads. It is a major weed in range and pasture land, a nuisance pest along rights-of-way and a looming nightmare for lands in conservation reserve programs. It can invade native grasslands, even where existing dense prairie vegetation exists. Glade communities are also prone to infestation, especially those with grazing histories and lacking buffers of undisturbed land.
Distribution in Missouri: 
Widespread, probably throughout the state.
Status: 
Invasive. Musk thistle is a native of Europe and Asia that was introduced into the United States as early as the 1850s. It is now widely naturalized in the United States and Canada, and is a bane to farmers. It, along with other invasive species, costs our country billions to battle.
Life cycle: 
Musk thistle can be a biennial, a winter annual or an annual. Plants typically overwinter as rosettes and send up flowering stalks the following spring, then can flower through October. Seeds mature and can begin dispersing in 7-10 days of flowering. A single plant can produce as many as 11,000 seeds. The seeds can remain viable for up to ten years.
Human connections: 
Musk thistle infestations are economically damaging because they compete with crops for light, space, nutrients and water. In pastures, its spiny foliage renders it unsuitable for livestock.
Ecosystem connections: 
Musk thistle spreads its dense basal rosette and crowds out native plant and grassland species through competition for resources. Grazers avoid this species, which gives musk thistle another competitive advantage over native plants and grasslands.