Silybum marianum, Blessed Milkthistle
Scientific Name: Silybum marianum
Common Name: Blessed Milkthistle
Also Called: Blessed Milk-thistle, Milk Thistle, Spotted Thistle, Variegated Thistle
Family: Asteraceae, Sunflower Family
Synonyms: (Carduus marianus, Mariana mariana)
Duration: Annual or, biennial.
Size: Up to 6 feet.
Growth Form: Forb/herb; rosette basal leaves; erect stems, coarse spiny thistle.
Leaves: Green; variegated with white veins and white splashes, large leaves up to 2 feet pinnately divided, lobes, clasping, margins also dentate and spine tipped.
Flower Color: Purple; flower heads up to 2 inches, borne singly on tips of stalks and in leaf axil; disk flowers only, bracts or phyllaries tomentose, with spines on margins and tips, sharply curved; fruit is an achene.
Flowering Season: May to September.
Elevation: Sea level to 2,500 feet.
Habitat Preferences: Roadsides, open fields and waste areas.
Recorded Range: In the United States Blessed Milkthistle has an unusual distribution found in most of the southern states and many northeastern states. It is common throughout most of Canada. In Arizona, it is recorded in central and southern counties.
North America & US County Distribution Map for Silybum marianum.
U.S. Weed Information: Silybum marianum is listed in 46 states and in: Weeds of the United States and Canada, and Weeds of the West. Plants included here may become weedy or invasive.
Invasive/Noxious Weed Information: Silybum marianum is listed as a Noxious Weed by Oregon and Washington. Plants included here are invasive or noxious.
Wetland Indicator: No data available.
Threatened/Endangered Information: No data available.
Comments: Blessed Milkthistle is a handsome European species introduced in the United States and sometime cultivated.
Photos taken May 31 roadside adjacent to agricultural area, Maricopa County, Arizona.