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

Blessed Milkthistle has purple flowers and the floral heads may be reddish-purple or purple. The flowering heads are solitary, and the flowers are large, between 2 and 4 inches (5-12 cm) across. Silybum marianum Blessed Milkthistle has bracts surrounding the floral heads (phyllaries) that are hairless and spreading with long tapered spine tips as shown in the photo. Silybum marianum Blessed Milkthistle has stems that are for the most part hairless or covered in dense, soft, often matted short hairs (tomentose) as shown here. Note that the leaves have spiny edges. Silybum marianum Blessed Milkthistle is in the Aster family and its fruit is a cypsela in a fuzzy wind-borne array as shown here. Silybum marianum Blessed Milkthistle flowers are on long leafless flowering stalks as seen here. Plants bloom from February or March through August or September and prefer elevations up to 2,600 feet (800 m). Silybum marianum

Scientific Name: Silybum marianum
Common Name: Blessed Milkthistle

Also Called: Blessed Milk-thistle, Cardus Marianus, Marian Thistle, Mary Thistle, Mediterranean Milk Thistle, Milk Thistle, Saint Mary's Thistle, Spotted Thistle and Variegated Thistle

Family: Asteraceae, Sunflower Family

Synonyms: (Carduus marianus, Mariana mariana)

Status: Introduced

Duration: Annual or biennial.

Size: 1 to 6 feet (.3-1.8 m) or more; 6.5 feet (2 m)

Growth Form: Forb/herb; starts out in a small rosette and quickly grows a large array of basal leaves up to 60 inches (152 cm); the plants are upright (erect); and the stems are hairless or slightly covered in dense, soft, often matted short hairs (tomentose), or thinly pilose, stems hollow out with age.

Leaves: Green; leaves have spiny edges, they are clasping, hairless, variegated, shiny green with milky-white venation; leaves are large, up to 2 feet (61 cm); oblong to lanceolate often pinnately lobed.

Flower Color: Purple; floral heads reddish-purple or purple; single (solitary) flower heads are large, between 2 and 4 inches (5-12 cm) across; flowers on a long leafless inflorescence; the bracts surrounding the floral heads (phyllaries) are hairless and spreading with long tapered spine tips as shown in the photos above; the fruit is a fuzzy wind-borne cypsela.

Flowering Season: February or March through August or September

Elevation: Sea level to 2,600 feet (800 m)

Habitat Preferences: Roadsides, meadows, open fields and waste areas.

Recorded Range: In the United States Blessed Milkthistle has a sporadic distribution scattered throughout the southern and a few northeastern states. It is also introduced and spread throughout most of Canada. In the southwest it is found in decent numbers in CA, AZ and with fewer populations in NM, NV and TX.

North America & US County Distribution Map for Silybum marianum.

North America species range map for Blessed Milkthistle, Silybum marianum:

North America species range map for Blessed Milkthistle, Silybum marianum: Click image for full size map.
Click image for full size map

U.S. Weed Information: Silybum marianum is listed in:

  • State noxious weed lists for 46 states;
  • Weeds of the United States and Canada;
  • 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:
  • Arkansas, “Noxious weed”;
  • Oregon, “List ‘B’ designated weed”;
  • Washington, “Class ‘A’ noxious weed”.

  • Plants included here are invasive or noxious.

    Wetland Indicator: Unknown

    Threatened/Endangered Information: Unknown

    Genus Information: In North America there are 2 species and 2 accepted taxa overall for Silybum. Worldwide, The Plant List includes 2 accepted species names and a further 4 scientific names of infraspecific rank for Silybum.

    The genus Silybum was published in 1763 by Michel Adanson, (1727-1806).

    In the Southwestern United States: there is 1 species of Silybum. Data approximate and subject to revision.

    Comments: Blessed Milkthistle is a handsome European species introduced in the United States and sometime cultivated. All parts of Blessed Milkthistle, Spotted Thistle or Variegated Thistle as they are also locally called, are toxic if ingested and may cause heavy losses of cattle and sheep. The leaves contain high levels of nitrates.

    Blessed Milkthistle is also cultivated as an ornamental.

    Photos taken May 31 roadside adjacent to agricultural area, Maricopa County, Arizona.

    Importance to Wildlife, Birds and Livestock
    Silybum marianum has small but attractive tubular flowers, the flowers and their seeds and plants may be visited by hummingbirds and/or small mammals including rodents and granivorous birds in search of food, nectar and protection through cover.

    However the vegetative parts, including leaves and stems, are known to be toxic to cattle and sheep.

    The genus “Silybum” (Sil'ybum:) is from the Greek name for a thistle that was used for food

    The genus Silybum was published in 1763 by Michel Adanson, (1727-1806).

    The species epithet marianum (maria'num:) according to “California Plant Names: Latin and Greek Meanings and Derivations”, compiled by Michael L. Charters, the name marianum is “referring to the story that the white marks on the leaves resulted from drops of milk shed while Mary nursed the Christ child. The species Silybum marianum has been called Our Lady's or blessed thistle...”.


    Date Profile Completed: 10/28/2012; updated 11/02/2020
    Arizona Flora, Kearney, Thomas H., Peebles, Robert H., 1960, University of California Press, Berkley and Los Angeles
    U.S. Dept. of Agriculture, Natural Resources Conservation Service on-line database and USGS ITIS search; accessed 11/02/2020.
    The Plant List (2013). Version 1.1. Published on the Internet;; accessed 11/02/2020.
    A.R. Bean (2020) Silybum marianum, in (ed.), Flora of Australia. Australian Biological Resources Study, Department of Agriculture, Water and the Environment: Canberra. [Date Accessed: 02 November 2020]
    David J. Keil, FNA | Family List | FNA Vol. 19, 20 and 21 | Asteraceae; Silybum, 1. Silybum marianum (Linnaeus) Gaertner, Fruct. Sem. Pl. 2: 378. 1791.;Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford.
    David J. Keil 2012, Silybum marianum, in Jepson Flora Project (eds.) Jepson eFlora, /eflora/eflora_display.php?tid=4918, accessed on November 01, 2020.
    Wikipedia contributors, 'Silybum marianum', Wikipedia, The Free Encyclopedia, 1 November 2020, 07:48 UTC, [accessed 1 November 2020]
    Sanda Rasic, Edita Stefanic, Ivan Stefanic; October 2009; Journal of Apicultural Research 48(4):298-299; Project: Economics of Beekeeping; accessed 11/02/2020.
    Seiler, John, Peterson, John, North American species range map courtesy of Virginia Tech, Dept. of Forest Resources & Environmental Conservation
    SEINet synonyms, scientific names, geographic locations, general information.
    Etymology:Michael L. Charters California Plant Names: Latin and Greek Meanings and Derivations; A Dictionary of Botanical and Biographical Etymology - (accessed 11/02/2020)
    IPNI (2020). International Plant Names Index. Published on the Internet, The Royal Botanic Gardens, Kew, Harvard University Herbaria & Libraries and Australian National Botanic Gardens. [Retrieved 02 November 2020].