Yellow Starthistle (Noxious Weeds of Colorado)

Yellow Starthistle

Centaurea solstitialis

Summary ⁸

Yellow starthistle (Centaurea solstitialis) originated from Northern Spain. It is a winter annual that is blue-green in color, has a vigorous taproot, and produces bright yellow flowers with sharp, stiff spines surrounding the base of the flower that extends up to ¾ of an inch long. Flowering occurs June-September. Yellow starthistle grows up to 4 feet tall. Basal leaves are 1-3 inches long and deeply lobed while upper leaves are smaller and narrower. Stems appear winged and both stem and leaves have a slight whitish nap covering them. Yellow starthistle spreads by seed with a single large plant producing up to 100,000 seeds. Plumed and plumeless seeds disperse at different times. Yellow starthistle is toxic to horses, causing a neurological disorder called chewing disease.

Source:
https://drive.google.com/file/d/1fSr_NTtT5hhxijR4WQGE3EJVu2KNlb06/view
http://www.cwma.org/YellowStarthistle.html

Identification ⁸

Height: 2-3 feet tall
Shape: Upright forb
Flowers: Yellow, 1/2 - 3/4 in long, single at ends of branches, sharp, straw-colored thorns up to 0.75 inches long. Flowers lose their petals but remain attached to the stems.
Stems: Rigid, branching, winged and covered with white cottony hairs
Leaves: Basal leaves are alternate,deeply lobed, 2-4 inches long and 1-1 1/2 inches wide. Upper leaves are narrow, edges smooth, sharply pointed. Young plants green, older plants grey-green and hairy
Fruit: Ray flowers produce seeds with pappus, disk flowers produce seeds without pappus. 100,000 seeds per plant, viable for 1-4 years
Toxic: YES - fatal to horses,
Root: Vigorous taproot, fast growing

Source:
https://drive.google.com/file/d/1fSr_NTtT5hhxijR4WQGE3EJVu2KNlb06/view
http://www.cwma.org/YellowStarthistle.html

Origin / Habitat ⁸

Yellow starthistle is originally native to Europe and the Mediterranean region. It is intolerant of shade and requires light on the soil surface for winter rosette and taproot development. Yellow starthistle is capable of establishing on deep, well-drained soils as well as on shallow, rocky soils that receive from 10-40 in of annual precipitation. Habitats for yellow starthistle include rangelands, pastures, roadsides, cropland, wastelands, and lower elevations. Over utilized grasslands are particularly susceptible to invasion.

Source:

https://drive.google.com/file/d/1fSr_NTtT5hhxijR4WQGE3EJVu2KNlb06/view
http://www.cwma.org/YellowStarthistle.html