Duration and Habit: Annual Herb
Slenderflower or winged thistle is a winter annual broadleaf weed that is similar in appearance to Italian thistle, C. pycnocephalus. Plants grow up to 100 cm tall with triangular shaped stem wings that are up to one centimeter and tipped with a spine. The underside of leaves and stems are covered with cobwebby hairs. Terminal inflorescences can contain from 5 to 15 small pinkish corollas. First flower buds have been observed as close as 4 to 6 inches from the rosette.
Ecological Threat: Has a tendency to form dense stands and is an aggressive annual which can interfere and displace native prairie grasses.
Biology & Spread: Flowers in early spring through summer (Apr-July). Seed is readily spread by the wind and is also dispersed by hay cutting and bailing operations. Likely to be seen in disturbed areas, roadsides, overgrazed pastures and utility right of ways.
History: Introduced to California, Oregon and the Pacific NW from Southern Europe (Mediterranean region. Unknown in North Central Texas until ~1990.
U.S. Habitat: Usually associated with pastures, disturbed areas, and vacant lots. Often invading native prairies.
U.S. Nativity: Introduced
Native Origin: Southern Europe
U.S. Present: CA, NJ, OR, PA, TX, WA
Distribution: North and Central Texas
Mechanical removal is known to be effective if done prior to seed dispersal but must be repeated for 3-5 years to exhaust the seed bank. Thistle is also responds to very dilute chemical treatments containing 2-4-D (personal communication with Curt Decker, Resource Conservation Biologist, Fossil Rim Wildlife Ranch).USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
Shinners and Mahler's Illustrated , Flora of North Central Texas, (G.Diggs, B. Lipscomp and R.J.O'kennon), BRIT Press 1999
Flora of North America @ www.efloras.org volumes 19,20 & 21 pages 91,94.
Gassmann, A. and L.T. Kok.2002. SLENDERFLOWER THISTLE (WINGED SLENDER OR SEASIDE THISTLE). in Biological Control of Invasive Plants in the Eastern United States. USDA Natural Resources Conservation Service website www.nrcs.usda.gov.
Google Search: Carduus tenuiflorus
Google Images: Carduus tenuiflorus
NatureServe Explorer: Carduus tenuiflorus
USDA Plants: Carduus tenuiflorus
Invasive Plant Atlas of the United States: Carduus tenuiflorus
Bugwood Network Images: Carduus tenuiflorus