Caribou County: www.cariboucounty.us
Weed List

  • Musk Thistle: Mature plants range in height from 1-1.5 m tall and have multi-branched stems. The leaves are dark green, coarsely bipinnately lobed, with a smooth, waxy surface and sharp yellow-brown to whitish spines at the tips of the lobes. The large globose flower heads, containing hundreds of tiny individual flowers, are 3-5 cm (rarely to 7 cm) diameter and occur at the tips of stems.
  • Leafy Spurge: It is a herbaceous perennial plant growing to 1-1.2 m tall, with several stems branched from the base. The stems are smooth, hairless or slightly hairy. The leaves are small, lanceolate, 4-8.5 cm long and up to 1 cm broad, with a slightly wavy margin. The flowers are small, produced in umbels with a basal pair of bright yellow-green petal-like bracts. Clusters of the bracts appear in late spring, while the actual flowers do not develop until early summer. All parts of the plant contain a toxic white milky sap.
  • Canada Thistle: It is a tall herbaceous perennial plant, forming extensive clonal colonies from an underground root system that sends up numerous erect stems each spring, reaching 1–1.2 m tall (occasionally more); the stems often lie partly flat by summer but can stay erect if supported by other vegetation. The leaves are very spiny, lobed, up to 15–20 cm long and 2–3 cm broad (smaller on the upper part of the flower stem). The inflorescence is 10–22 mm diameter, pink-purple, with all the florets of similar form (no division into disc and ray florets). The flowers are usually dioecious, but not invariably so, with some plants bearing hermaphrodite flowers. The seeds are 4–5 mm long, with a feathery pappus which assists in wind dispersal.
  • Scotch Thistle: Cotton Thistle is a biennial plant, producing a large rosette of spiny leaves the first year. The plants typically germinate in the autumn after the first rains and exist as rosettes throughout the first year, forming a stout, fleshy taproot that may extend down 30 cm or more for a food reserve. In the second year, the plant grows (0.2-) 0.5–3 m tall and a width of 1.5 m. The leaves are 10–50 cm wide, are alternate and spiny, often covered with white woolly hairs and with the lower surface more densely covered than the upper. The leaves are deeply lobed with long, stiff spines along the margins. Fine hairs give the plant a greyish appearance. The massive main stem may be 10 cm wide at the base, and is branched in the upper part. Each stem shows a vertical row of broad, spiny wings (conspicuous ribbon-like leafy material), typically 2-3 cm wide, extending to the base of the flower head.
  • Dalmation Toadflax: Dalmation Toadflax was introduced as an ornamental plant from the Mediterranean in the late 1800’s. Flowers are similar to that of a snapdragon and large plants produce nearly 1/2 million seeds. Dalmation Toadflax loves arid rangelands, pastures, railways and waste areas and is primarily a weed of the Intermountain West and California.
  • Yellow Toadflax: It is a perennial plant with short spreading roots, erect to decumbent stems 15–90 cm high, with fine, threadlike, glaucous blue-green leaves 2-6 cm long and 1-5 mm broad. The flowers are similar to those of the snapdragon, 25-33 mm long, pale yellow except for the lower lip which is orange, borne in dense terminal racemes from mid summer to mid autumn. The fruit is a globose capsule 5-11 mm long and 5-7 mm broad, containing numerous small seeds.
  • Hounds Tongue: It is a herbaceous plant of the family Boraginaceae, found in most parts of Europe, and also North America where it was accidentally introduced. It can be either annual or biennial, with reddish-purple flowers blooming between May and September. It lives in wet places, waste land and hedges.
  • Black Henbane: Can be toxic, even fatal, to animals in low doses. Its name dates at least to 1265. The origins of the word are unclear but "hen" probably originally meant death rather than referring to chickens. Hyoscyamine, scopolamine, and other tropane alkaloids have been found in the foliage and seeds of the plant. Common effects of henbane ingestion in humans include hallucinations,[1] dilated pupils, restlessness, and flushed skin. Less common symptoms such as tachycardia, convulsions, vomiting, hypertension, hyperpyrexia and ataxia have all been noted.
  • Spotted Knapweed: It has been introduced to North America where it is sometimes considered an invasive plant species in the Rocky Mountains. Biological pest control agents are sometimes used against this plant, including the moths Agapeta zoegana and Metzneria paucipunctella, the weevils Bangasternus fausti, Larinus obtusus and Cyphocleonus achates, and the fruit fly Chaetorellia acrolophi. Knapweed is a pioneer species found in recently disturbed sites or openings. Once it has been established at a disturbed site, it continues to spread into the surrounding habitat.
  • Russian Knapweed: Russian Knapweed (Acroptilon repens) is a bushy rhizomatous perennial, up to 8 dm tall. Stems and leaves are finely arachnoid-tomentose becoming glabrous and green with age. The rosette leaves are oblanceolate, pinnately lobed to entire, 2-3 cm wide by 3-8 cm long. The lower cauline leaves are smaller, pinnately lobed; the upper leaves become much reduced, sessile, serrate to entire. The heads are numerous terminating the branches. Flowers are pink to purplish, the marginal ones not enlarged.
  • Purple Loosestrife: Lythrum salicaria is an herbaceous perennial plant, that can grow 1-1.5 m tall, forming clonal colonies 1.5 m or more in width with numerous erect stems growing from a single woody root mass. The stems are reddish-purple or red to purple and square in cross-section. The leaves are lanceolate, 3-10 cm long and 5-15 mm broad, downy and sessile, and arranged opposite or in whorls of three.
  • Whitetop: Whitetop is a perennial herb that reproduces by seeds and by horizontal creeping roots. The stem is stoutish, erect or spreading, 10 to 80 cm tall, branched, covered sparsely with ash-colored soft hairs to heavily covered. The leaves are alternating, simple, and mostly toothed. The basal leaves are 4 to 10 cm., have a slight stem (petiole), and are long and flat, lance-shaped to egg-shaped, with the narrow end attached to the stalk. On the upper part of the stem the leaves are attached directly to the stalk (sessile), are 2 to 6.5 cm. long, are oblong or tapering the point, with broad bases that clasp the stalk.
Caribou County Idaho

Caribou County Courthouse | 159 South Main | Soda Springs, Idaho 83276 | (208) 547-4324

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