T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Silybum marianum (Variegated Thistle)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Tribe: Cynareae
Genus: Silybum
Species: S. marianum
Binomial name: Silybum marianum
Common name: Variegated Thistle, Milk thistle, , Marian Thistle, Mary Thistle, Saint Mary's Thistle, Mediterranean Milk Thistle, Cardus marianus, Bblessed milk thistle,

Silybum marianum is an annual or biannual plant of the Asteraceae family. 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. In New Zealand it is considered an invasive weed.
It grows 40 to 100 cm tall. The stem is grooved and more or less cottony.
The leaves are oblong to lanceolate. They are either lobate or pinnate, with spiny edges. They are hairless, shiny green, with milk-white veins. The flower heads are 4 to 5 cm long and wide, of red-purple colour. It flowers November throught to March depending on the area. The bracts are hairless, with triangular, spine-edged appendages, tipped with a stout yellow spine. The achenes are black, with a simple long white pappus, surrounded
by a yellow basal ring.

Due to potassium nitrate content, the plant has been found to be toxic to cattle and sheep. When potassium nitrate is eaten by ruminants, the bacteria in theanimal's stomach breaks the chemical down, producing a nitrite ion. Nitrite ion then combines with hemoglobin to produce methaemoglobin, blocking the transport of oxygen. The result is a form of oxygen deprivation.
The medicinal parts of the plant are the ripe seeds.