Carnegiea gigantea, Giant Saguaro

Southwest Desert Flora

Home to the plants of the Sonoran, Chihuahuan and Mojave Deserts

Cirsium ochrocentrum, Yellowspine Thistle

Silybum marianum, Blessed Milkthistle

Silybum marianum, Blessed Milkthistle, Southwest Desert Flora Silybum marianum, Blessed Milkthistle, Southwest Desert Flora Silybum marianum, Blessed Milkthistle, Southwest Desert Flora   Silybum marianum, Blessed Milkthistle, Southwest Desert Flora Silybum marianum, Blessed Milkthistle, Southwest Desert Flora   Silybum marianum, Blessed Milkthistle, Southwest Desert Flora

Scientific Name: Silybum marianum
Common Name: Blessed Milkthistle
Also Called: Blessed Milk-thistle, Milk Thistle, Spotted Thistle and Variegated Thistle
Family: Asteraceae, Sunflower Family
Synonyms: (Carduus marianus, Mariana mariana)
Status: Introduced
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.

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.

Genus Information: 1 species in Silybum in the United States.

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.

Date Profile Completed: 10/28/2012; Updated, 07/26/2015
References:
U.S. Dept. of Agriculture, Natural Resources Conservation Service on-line database
Arizona Flora, Kearney, Thomas H., Peebles, Robert H., 1960, University of California Press, Berkley and Los Angeles
The Jepson Manual, Citation: http://ucjeps.berkeley.edu/interchange/I_treat_indexes.html Sun Oct 28 08:27:32 2012
David J. Keil, FNA | Family List | FNA Vol. 19, 20 and 21 | Asteraceae | Silybum, Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford. (accessed 10/28/2012)
SEINet for synonyms, scientific names and recorded geographic locations, http://swbiodiversity.org/seinet/
Noxious Weed Information: - Silybum marianum (L.) Gaertn.
Arkansas: - Silybum – thistle - Noxious weed, Oregon: - milk thistle - "B" designated weed, Washington: - milk thistle - Class A noxious weed, milk thistle Noxious weed seed and plant quarantine
U.S. Weed Information: - Silybum marianum (L.) Gaertn. - common names: blessed milkthistle, milk thistle, spotted thistle, variegated thistle, Silybum thistle
STATE - Assorted authors. State noxious weed lists for 46 states. State agriculture or natural resource departments.
SWSS - Southern Weed Science Society. 1998. Weeds of the United States and Canada. CD-ROM. Southern Weed Science Society. Champaign, Illinois.
WSWS - Whitson, T.D. (ed.) et al. 1996. Weeds of the West. Western Society of Weed Science in cooperation with Cooperative Extension Services, University of Wyoming. Laramie, Wyoming.