blessed milkthistle

Asterales > Asteraceae > Silybum marianum (L.) Gaertn.
Synonym(s): blessed milk-thistle, milk thistle, spotted thistle, variegated thistle

Blessed milkthistle is an annual/biennial herb native to the Mediterranean region. Plants range from 2-6 ft. (0.6-1.8 m) in height, depending on soil moisture. Leaves have shiny, green upper surfaces and are noticeably variegated with white markings. Basal leaves are 6-28 in. (15-70 cm) long with spiny margins. Much smaller cauline (stem) leaves clasp the stem. Flowering occurs from April to July, when purple thistle flower heads develop at the apex of the stems. Flower heads are 0.8-2.5 in. (2-6 cm) in diameter at the base and are enclosed in a projecting, spiny involucre. Fruit are black and brown achenes that are approximately 1/3 in. (6-8 mm) long, slightly flattened with a ring of bristles at the apex. Plants invade roadsides, ditches, disturbed areas and fertile fields. Milk thistle can be poisonous to livestock, especially during periods of wilt from drought, mowing or herbicide treatment.


Identification, Biology, Control and Management Resources


Selected Images from Invasive.org

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Plant(s); habit
Forest & Kim Starr, U.S. Geological Survey, Bugwood.org
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Foliage;
Charles T. Bryson, USDA Agricultural Research Service, Bugwood.org
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Plant(s);
Charles T. Bryson, USDA Agricultural Research Service, Bugwood.org
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Plant(s);
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Flower(s);
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Flower(s);
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Infestation;
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Infestation;
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Plant(s); in flower
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Seed(s);
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Diagram or Graphic; Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 3: 555.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
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Invasive Reference(s):

Check Invasive.org for most current lists.
  • Alabama - IPC List
  • California - Invasive Plant Inventory
  • Oregon - Noxious Weed Law
  • Washington - Noxious Weed Law
  • Invasive Plants of the Upper Midwest


External Links


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