Arizona Wild Flowers
Wildflower Pictures And Photos

Yellow Star Thistle, Centaurea solstitialis

Yellow Star Thistle, Centaurea solstitialis

Yellow Star Thistle, Sunflower Family (Asteraceae) (Centaurea solstitialis)	Native To Southern Europe
Toxic To Horses Causes "chewing disease."	Once It Invades An Area It Becomes Genetically Adapted Then Population Explodes
It Has Taken Over Parts Of Califotnia	Small Populations Must Be Eradicated!

Yellow Star Thistle Centaurea solstitialis, Sunflower Family ( Asteraceae ), Yellow Star Thistle. Also called: yellow star thistle, geeldissel, golden star thistle, St. Barnaby's thistle, yellow centaury, yellow cockspur. Yellow starthistle is a gray-green to blue-green annual or biennial invasive weed with a deep taproot. The stems are erect, 24 inches tall, freely branching, covered with a thin tomentum and prominently winged by decurrent leaf bases. The basal leaves are lyrate or pinnatifid, early deciduous, 2" wide to 9" long; middle and upper leaves are smaller becoming linear and entire. The yellow flowers are in heads that terminate the branches. The middle and outer involucral bracts are spine tipped, the larger central spines commonly 4" - 10" long; inner bracts unarmed. Pappus lacking on marginal flowers, that of others 2" - 4" long. The fruit is a yellowish achene with brown marbling. Height: 24" tall and usually less wide. Flowers: Yellow flowers in heads that terminate the branches. The middle and outer involucral bracts are spine tipped, the larger central spines commonly 4" - 10" long; with inner bracts unarmed. Pappus is lacking on marginal flowers, that of others is 2" - 4" long. Blooming Time: January to October. Fruit & Seeds: Pappus-bearing seed usually dispersed after the flowers senesce. Non-pappus-bearing seeds are retained in the seed head. Leaves: The basal leaves are lyrate or pinnatifid, early deciduous, 2" wide to 9" long; middle and upper leaves are smaller becoming linear and entire. Found: Found throughout Arizona. near waterways. Elevation: 0 - 6000 Feet. Habitat: Riparian habitats. Miscellaneous: Flowering Photos Taken , March 31, 2003. In Glendale.