Family: Asteraceae, Aster view all from this family
Description Introduced. A slender, repeatedly branched, open, broom-like plant with many pink-lavender, rayless flower heads at ends of stiff, soft-hairy stems.
Flowers: Head about 3/8" (10 mm) wide, slightly longer and tapered toward top, with bright pink-lavender (rarely white) disk flowers at top, those around edge of head each 1/2-1" (1.5-2.5 cm) long; corolla of each disk flower with 5 long slender lobes; prickly bracts on side of head with blackish fringed tip.
Leaves: Those at base 4-8" (10-20 cm) long, deeply pinnately divided into narrow lobes, often with glandular spots; those on stem smaller, uppermost ones often not lobed.
Height: 12-48" (30-120 cm).
Warning If this noxious weed is extensively handled, gloves are advised; there is some evidence that it causes tumors on the hands.
Flower June-September.
Habitat Disturbed areas, often along roadsides, waste places, fields.
Range Washington south to California and east across much of southern Canada and the United States; south to Florida, west to Louisiana.
Discussion This European import has become a scourge across the United States and southern Canada. It grows in thick stands, and where ever it spreads, all other vegetation dies out. Scientists only very recently discovered that this plant gives off a poison from its roots that kills off other plants. No native American species has yet proved able to survive in its presence. In an unsuccessful attempt to control the plant, flies have been introduced whose grubs feed upon the developing seeds. Even though seed production is reduced 30-85 percent by the grubs, there are still hundreds of seeds to spread the species. This plant is also commonly known as C. maculosa, there having possibly been an early nomenclatural mix-up of plants in these two variable European species. Two similar annuals are Cornflower (C. cyanus), with bright blue flower heads, and Star Thistle, (C. americana), a showy southwestern species with larger, pink disk flowers and smaller white disk flowers.
