blessed milkthistle
Silybum marianum (L.) Gaertn.


Silybum marianum is an annual or biennial herb that ranges from 2-6 ft. (0.6-1.8 m) in height.
Leaves have shiny, green upper surfaces and are noticeably variegated with white markings. Basal leaves are 6-28 in. (15.2-71.1 cm) long with spiny margins. Much smaller stem leaves clasp the stem.
Purple thistle flower heads develop at the apex of the stems. They are 0.8-2.5 in. (2-6.4 cm) in diameter at the base and are enclosed in a projecting, spiny involucre. Flowers from April to July.
Fruit are black and brown achenes that are about 0.3 in. (0.85 cm) long, slightly flattened with a ring of bristles at the apex.
Ecological Threat
S. marianum invades roadsides, ditches, disturbed areas and fertile fields. It is native to the Mediterranean region. S. marianum can be poisonous to livestock, especially during periods of wilt from drought, mowing or herbicide treatment.


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EDDMapS Distribution

EDDMapS Distribution - This map is incomplete and is based only on current site and county level reports made by experts, herbaria, and literature. For more information, visit

State Regulated List

State Regulated List - This map identifies those states that list this species on their regulated list. For more information, visit

Taxonomic Rank

Kingdom: Plantae
Phylum: Magnoliophyta
Class: Magnoliopsida
Subclass: Asteridae
Order: Asterales
Family: Asteraceae
Genus: Silybum
Subject: Silybum marianum (L.) Gaertn.

Synonyms and Other Names

Other Common Names:
blessed milk-thistle, milk thistle, spotted thistle, variegated thistle

Related Scientific Names:
Carduus marianus (L.) Gaertn. (Synonym)
Mariana marianum (L.) Gaertn. (Synonym)


Plants - Forbs/Herbs