Cirsium undulatum

Cirsium undulatum
Cirsium undulatum
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Tribe: Cynareae
Genus: Cirsium
Species: C. undulatum
Binomial name
Cirsium undulatum
(Nutt.) Spreng.

Cirsium undulatum is a species of thistle known by the common names wavyleaf thistle and gray thistle. It is native to much of central and western North America from Canada to Mexico, and present outside of its native range as an introduced species. It is widespread and found in many habitat types. It is a perennial herb exceeding two meters in maximum height. The stem branches a few times toward the top of the plant if at all. The leaves are very wavy along the edges and usually cut into shallow toothed lobes. The longest near the base of the plant are 30 centimeters in maximum length. The inflorescence holds one or more flower heads each up to 5 centimeters long and wide. The head is lined with spiny phyllaries of different shapes. The flowers in the head are white to lavender to pink and up to 5 centimeters long. The fruit is an achene a few millimeters long with a pappus which may be up to 4 centimeters in length.

There are at least two varieties: var. Tracyi, which is restricted to Colorado and Utah and var. undulatum, which is more widespread.

Cirsium undulatum var Tracyi has been shown to have its seed production reduced by an exotic weevil Larinus planus which was released to control canada thistle.

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