Natives ... Do Not Disturb! he Lake Tahoe Basin is home to many species Tof wildflowers, including beneficial native Snowy Thistle Know thistles that provide food and habitat for local wildlife. However, many areas in the basin are (Cirsium occidentale var. candidissimum) infested with several species of invasive thistles ¤ Biennial that crowd out desirable plant species, altering ¤ Has eye-catching white stems and leaves and Your plant communities. bright-red flowers. Not only are these invasive weeds difficult to ¤ Flower head is cylinder-shaped with a single control and unpleasant to walk through, they also flower at the end of the stem. Thistles! displace native vegetation, decrease wildlife habitat, ¤ Plant is white and wooly. alter normal ecological processes, and reduce ¤ Whitish leaves are recreational uses. In addition, they cost us millions long, narrow, and Learn to distinguish desirable native of dollars each year in treatment costs, decreased lobed. Anderson’s thistles from weedy invasive thistles land productivity and decreased land value. Thistle in the Lake Tahoe Basin If you look closely, there are many clues that will help you identify the various local thistles. When (Cirsium andersonii) you find invasive weeds, report the location to the ¤ Biennial By Susan Donaldson, appropriate county (see back panel). Ask experts ¤ Flower head is cylinder-shaped with a single University of Nevada Cooperative Extension to confirm the identity of invasive thistles before flower at the end of the stem. applying control measures. ¤ Flower color is rose-red to reddish in color. ¤ Leaves are divided and wavy, with spiny edges. Quick Guide to ¤ Stems are purplish and thornless. Identifying Thistles ¤ Appears more delicate than other thistles. ¤ Is most commonly confused with bull thistle. Invasive Thistles Elk Thistle (Cirsium scariosum) Bull thistle Vase-shaped flower; spiny, winged stem; ¤ Biennial rough, bumpy leaves ¤ Stemless, white to pale-lavender flowers For more information, contact: Canada thistle Smallest thistle; very spiny; grows in extend directly from the rosette. NEVADA moist locations ¤ Leaves are lobed, Douglas County: Musk thistle Largest flower; single, sometimes nod- somewhat spiny Weed District ding flower at end of stem; hairless (775) 782-9835 and pale-green. leaves Washoe County: Scotch thistle Largest thistle; grayish-green hairy ap- ¤ Usually has no University of Nevada Cooperative Extension pearance; soft, hairy leaves stems. Forms flat (775) 784-4848 Native Anderson’s Thistle at Lake Tahoe Native Thistles to the ground; CALIFORNIA generally less El Dorado County: Anderson’s thistle No spines on stems; red, cylindrical than 1 foot tall. Department of Agriculture flower (530) 621-5520 Elk thistle Flat, no stems; pale flower Placer County: Snowy thistle Whitish appearance; red flowers Brochure printing funded by USDA Forest Service, Department of Agriculture State and Private Forestry Program (530) 889-7372 Invasive Thistles … Management Required! Invasive Thistles … Management Required!

Bull Thistle (Cirsium vulgare) Scotch Thistle (Onopordum acanthium) ¤ Biennial ¤ Biennial ¤ Vase-shaped flowers occur in clusters at the ¤ Flowers are in groups of two or three on ends of the branches, and are pink to purple in branched stems. color. ¤ Flowers are purple, and flowers heads resem- ¤ Tops of leaves are rough, with a sandpapery ble a flattened globe. texture, and undersides of leaves are cottony ¤ Leaves are very hairy, with a grayish-green ap- and soft. pearance. ¤ Leaves have a prominently raised main vein. ¤ Stems are spiny and winged. ¤ Stems have spiny wings. ¤ Grows to 10 feet tall.

Management: Management: Dig, removing at least 2 inches of root. Dig, removing at least 2 inches of root. Chemical controls are available. Chemical controls are available.

Canada Thistle (Cirsium arvense) Musk ¤ Perennial ¤ Multiple small flower heads grow in clusters on Thistle each stem. (Carduus nutans) ¤ Flowers are light-purple to white with teardrop-shaped heads. ¤ Biennial ¤ Bracts are small and flat against flower head ¤ Single, very large, disk-shaped flowers are at with weak tips; they are not spiny. the ends of bent, naked stems. ¤ Leaves are smooth, deeply lobed, and ¤ Flowers are deep-pink to purple. extremely spiny. ¤ Purplish bracts are large and spiny. ¤ Grows in moist locations. ¤ Leaves are smooth, with prominent light-green midribs and spiny edges. Management: Pulling and cutting do not provide control. Management: Chemical applications must be repeated for Dig, removing at least 2 inches of the root. several years. Chemical controls are available.

Invasive Thistles … Management Required! Invasive Thistles … Management Required!