Definition

Noun: 1. A tall Old World biennial thistle (Silybum marianum) with large, glossy, dark green leaves marked with white veins or blotches and purple flower heads. It is known for its medicinal properties, particularly for liver health, and has been naturalized in regions like California and South America. 2. Any of several Old World coarse, prickly-leaved shrubs and subshrubs (e.g., in the genus Sonchus) that have milky juice and yellow flowers. These plants are widely naturalized and are often considered noxious weeds in cultivated soil.

Usage and Examples

• Referring to the medicinal plant (Silybum marianum):
  • The herbalist recommended a tea made from milk thistle to support liver function.
  • Milk thistle is easily identified by the distinctive white markings on its leaves.
• Referring to weedy shrubs (e.g., Sonchus species):
  • The field was overrun with milk thistle, its yellow flowers dotting the landscape.
  • Farmers work hard to control milk thistle, as it can quickly invade crops.

Advanced Usage

• "Milk thistle extract": A common supplement derived from the seeds of .
  • She takes milk thistle extract daily as part of her wellness routine.

Variants and Related Words

• Holy thistle: Another common name for .
• Lady's thistle: Another common name for .
• Silymarin: The active compound found in the seeds of , believed to have hepatoprotective effects.
• Sow thistle: A common name for plants in the genus, which are often included in the broader, weedy definition of "milk thistle."

Synonyms

• For : Holy thistle, Lady's thistle, Mary thistle.
• For weedy types: Sow thistle (specific to ), prickly weed.

Notes on Meaning

The term "milk thistle" has two primary meanings in botany and common usage: 1. The specific, valued medicinal plant, Silybum marianum. 2. A more general category of weedy, prickly plants with milky sap, primarily in the genus Sonchus. The intended meaning is usually clear from context, with medicinal or health contexts referring to the first definition and agricultural or weed-control contexts often referring to the second.

Noun

1. tall Old World biennial thistle with large clasping white-blotched leaves and purple flower heads; naturalized in California and South America
2. any of several Old World coarse prickly-leaved shrubs and subshrubs having milky juice and yellow flowers; widely naturalized; often noxious weeds in cultivated soil