Cirsium undulatum
Encyclopedia
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.
Cirsium
Cirsium is a genus of perennial and biennial flowering plants in the Asteraceae, one of several genera known commonly as thistles. They are more accurately known as Plume thistles. These differ from other thistle genera in having feathered hairs to their achenes...
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
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
. 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
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
holds one or more flower heads
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
each up to 5 centimeters long and wide. The head is lined with spiny phyllaries
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
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
Achene
An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...
a few millimeters long with a pappus
Pappus (flower structure)
The pappus is the modified calyx, the part of an individual disk, ray or ligule floret surrounding the base of the corolla, in flower heads of the plant family Asteraceae. The pappus may be composed of bristles , awns, scales, or may be absent. In some species, the pappus is too small to see...
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
Larinus planus
Larinus planus is a species of true weevil. It is used as an agent of biological pest control against the noxious weed canada thistle ....
which was released to control canada thistle.
External links
- Jepson Manual Treatment
- USDA Plants Profile
- Flora of North America
- Photo gallery
- http://web.wits.ac.za/NR/rdonlyres/CD7EB87D-64DC-419C-95BA-2F1A7E60329D/0/LoudaandOBrien2002.pdf