Wyoming Weed & Pest Designated List

Saltcedar (Tamarix spp.)


Saltcedar is a shrub or tree-like plant that invades riparian habitats, displacing native plants and using huge quantities of water.

Saltcedar branches have reddish brown bark,small flat leaves that resemble evergreens, and pink or white five-petaled flowers. The seeds are tiny and similar in size and color to pepper, and each seed has a pappus which allows it to float long distances in water or move in the wind.

Diffuse knapweed (Centaurea diffusa Lam.)


Diffuse knapweed is perennial, biennial, or sometimes annual weed that produces new shoots from a tap root each year. White or purple flowers appear at the end of each shoot. A single large stem and many branches and leaves are a sage green color. It differs from spotted knapweed in that is has a terminal spine instead of many branches from the base.

Spotted knapweed (Centaurea maculosa Lam.)


Spotted knapweed is a very aggressive invasive plant that releases toxins that reduce the growth of forage around it. This perennial has multiple stems growing from the rosette, and alternate sage green leaves. Flowers begin as bulb shapes, and flowers out with many purple or white. Spotted knapweed flowers are larger than Russian knapweed, and flower heads have a spotted appearance.spotted knapweed, noxious weed 8-2009 004


Houndstongue (Cynoglossum officinale L.)


Houndstongue is a biennial that grows in a leafy rosette the first year, and shoots stems and flowers in the second year. It is named for it’s heavy, tongue shaped, alternate leaves have a distinct rough, hairy feel, like a dog’s tongue.  Flowers are a deep red or purple with small crystals in the center. The seeds are small disks with barbs that allow them to cling on to people and animals, which is how they are dispersed.  Houndstongue contains pyrrolizidine alkaloids that cause liver failure in horses and cattle.

Dyers woad (Isatis tinctoria L.)


Dyers woad begins as a rosette with small, long tear drop shaped leaves that have a white spine in the center. It grows up to three feet tall with many branching stems, bluish-green alternated leaves that have a white spine, and bright yellow flowers that appear late in the season. Dyers woad was originally cultivated as a source of blue dye, and it is allelopathic, which mean that it produces chemicals which inhibit growth in other plants close by.

dyers woad

Musk thistle (Carduus nutans L.)


Musk thistle is a biennial that grows as only a rosette in the first year, and shoots in the second year.  Leaves have a frosted appearance, and white spines. It has very large bracts beneath purple flowers with sharp spines beneath.  Musk thistle reproduces only from seeds, and not from root systems.