Thistle is a type of flowering plant that is notable for having leaves with prickles located on their margins. Thistle is generally part of the Asteraceae family. In some cases, prickles show up all over thistle, such as on the flat areas of leaves and on the stems' surfaces. They are non-woody plants, and usually are annuals.
There are many different varieties of thistle within the Asteraceae family. Some well-known types of thistle include Syrian thistle (Notobasis), carline thistle (Carlina), sow thistle (Sonchus), globethistle (Echinops), star thistle (Centaurea) and oyster thistle (Scolymus).
In floriography (known commonly as "the language of flowers," there is some symbolism attached to thistle. In ancient Celtic culture, thistle symbolizes character nobility. It also symbolizes nobility of birth. In Scotland, thistle symbolizes the Order of the Thistle, which is a noteworthy chivalric order.
The flowers of thistle are a common source of nectar for various different species of butterflies, such as the high brown fritillary, the small pearl-bordered fritillary, the dark green fritillary and the pearl-bordered fritillary.
Thistle is considered to be a weed and therefore a pest to gardens and lawns. This is due to the fact that thistle competes against grain crops and forage (such as wheat and clover). Musk and Canada thistles are considered to be particularly problematic. Some of the ways thistle can be controlled is by herbicides and mechanical control (such as cutting thistle under the ground in order to stop regrowth from occurring).
Since thistle is often considered to be a pest, it is not often cultivated. However, thistle thrives in soil that has low levels of calcium. It also does well with abundant amounts of iron and low or complexed levels of phosphorus. Soil with large amounts of anaerobic bacteria and compacted soil is also preferable for thistle.