Thistle is a term used to describe certain plants in the family Asteraceae, which have prickly leaves and often pink or purple flowers. The most common type of thistle is the spear thistle (Cirsium vulgare), also known as the creeping thistle. Other types include the Scotch thistle (Onopordum acanthium) and the plumeless thistle (Carduus pycnocephalus). Thistles are often considered weeds due to their invasive nature, but they can also be cultivated as ornamental plants in gardens.