Thistle

Milk thistle flowerhead

Thistle is the common name of a polyphyletic group of flowering plants characterised by leaves with sharp spines or prickles on the margins, mostly in the plant family Asteraceae. Their prickles often occur all over the plant, including on the stem and flat parts of the leaf. These are an adaptation to protect the plant against herbivorous animals, discouraging them from feeding on the plant.

Heraldry

In the "Language of Flowers", the thistle burr is an ancient Celtic symbol of nobility of character as well as of birth; for the wounding or provocation of a thistle yields punishment. For this reason the thistle was subsumed as a device of The Most Ancient and Most Noble Order of the Thistle, the highest order of Scottish chivalry.

Another story is that a Viking attacker stepped on one at night and cried out, so alerting the defenders of a Scottish castle. Whatever the justification, the national flower of Scotland is the thistle - either Cirsium vulgare, Cirsium acaule, or Onopordum acanthium. It is found in many Scottish symbols and in the names of several Scottish football clubs.

Place names

Carduus is the Latin for a thistle (hence cardoon), and Cardonnacum is the Latin for a place with thistles. This is believed to be the origin of name of the Burgundy village of Chardonnay, Saône-et-Loire, which in turn is thought to be the home of the famous Chardonnay grape variety.

Taxa

Thistledown, a method of seed dispersal by wind. The tiny seeds are an important food for goldfinches and some other small birds.

Genera in the Asteraceae with the word thistle often used in their common names include:

• Arctium – Burdock
• Carduus – Musk Thistle and others
• Carlina – Carline thistles
• Centaurea – Star thistle
• Cicerbita – Sow thistle
• Cirsium – Common Thistle, Field Thistle and others
• Cnicus – Blessed thistle
• Cynara – Artichokes, Cardoon
• Echinops – Globethistle
• Notobasis – Syrian thistle
• Onopordum – Cotton thistles, also known as Scots thistle or Scottish thistle
• Scolymus – Golden thistle or oyster thistle
• Silybum – Milk thistles
• Sonchus – Sow thistles

Plants in families other than Asteraceae which are rarely also called thistle include:

• Salsola – Saltwort, tumbleweed or Russian thistle (family Amaranthaceae)