Silybum marianum is a species of thistle. It has various common names including milk thistle, blessed milkthistle, Marian thistle, Mary thistle, Saint Mary's thistle, Mediterranean milk thistle, variegated thistle and Scotch thistle (though not to be confused with Onopordum acanthium or Cirsium vulgare). This species is an annual or biennial plant of the family Asteraceae. This fairly typical thistle has red to purple flowers and shiny pale green leaves with white veins. Originally a native of Southern Europe through to Asia, it is now found throughout the world. Description Milk thistle is an upright herb that can grow to be tall and has an overall conical shape. The approximate maximum base diameter is . The stem is grooved and may be covered in a light cottony fuzz. The largest specimens have hollow stems. The leaves are oblong to lanceolate and 15–60 cm long and typically pinnately lobed, with spiny edges like most thistles. They are hairless, shiny green, with milk-white veins. The flower heads are 4 to 12 cm long and wide, of red-purple colour. They flower from June to August in the North or December to February in the Southern Hemisphere (summer through autumn). The flower head is surround by bracts which are hairless, with triangular, spine-edged appendages, tipped with a stout yellow spine. The fruits are black achenes with a simple long white pappus, surrounded by a yellow basal ring. A long pappus acts as a "parachute", supporting seed dispersal by wind. Distribution and habitat Silybum marianum is native to the Mediterranean region of Europe including Greece (mostly in Crete), east into Iran and Afghanistan. It is possibly native near the coast of southeast England. S. marianum has been widely introduced outside its natural range, for example into North America, Hawaii, Australia, New Zealand, Colombia where it is considered an invasive weed. Additionally, today it also spreads as invasive plant in almost all of Europe as a consequence of field cultivation. Silybum marianum establishes itself in sunny, warm ruderal meadows in regularly disturbed places such as rubble deposits, at the foot of south-exposed walls or villages and on urban fallow land or on cattle pastures. However, it does not prefer dry, stony soils. Milk thistle has been potentially observed to modify fire regimes in its invasive range. Its invasion into new habitats may also be encouraged by fire. The "giant thistle of the Pampas" reported by Darwin in