There are many species of thistle, which are mostly part of the Asteraceae family. The word “thistle” is often used to refer to a specific genera of the plant. But it can also be used to define a wider range of prickly flowering plants.

Cirsium has about 62 species of thistle which are the most common in North America. These Cirsium species have branched, feather hairs on their seeds, which makes their seeds spread easier by the wind. Canada thistle and bull thistle, varieties of cirsium, are both considered invasive species in North America.

Carduus thistles are also known as plumeless thistles. They are not native to North America, but are nevertheless widespread. Carduus thistles differ from Cirsium species because they have single stranded stems with spine wings. Many are annuals or biennials instead of perennials. Types of Carduus thistles include musk thistle, Italian thistle, slenderflower thistle and plumeless thistle.

It is always best to plant native species, if this is not possible then be very careful when growing them. Unfortunately, the invasive nature of this plant has caused many countries to declare war on several species of thistles. Australia’s parliament imposed heavy fines on those that do not control thistles on their land.

Species of thistle are very important for biodiversity, since they are a food source for pollinators. These plants are one of the best producers of nectar, which is valued by bumblebees, moths and butterflies including the “painted lady”.  Several types of birds, including finches, eat thistle seeds. Most of these plants are edible, including artichoke. Milk thistle (which has silymarin) and blessed thistle are species of thistle that have medicinal benefits.

Species of Thistle

Scottish Thistle (Onopordum acanthium)

Legendary Scottish thistle is said to have saved the Scottish army from a Norse invasion. One barefoot Norseman stepped on this plant causing him to cry out in pain, thus letting the Scottish know about their presence. It is said that this occurred during the Battle of Largs. Thistle has been the national emblem of Scotland since the times of King Alexander III. This plant is seen in local coins, used in football clubs and is also given as badges in the army.

Onopordum acanthium is the species of thistle known as Scottish thistle, which is also called cotton thistle. However, it is unlikely that this variety of thistle was the one from the legend since it is not native to Scotland and it was not found in medieval times. It is believed to have been introduced prior to the 16th century. Spear thistle (Cirsium vulgare) is abundant in Scotland and probably was thistle from the legend. This variety of thistle is also the symbol of Lorraine in France.

Scottish thistle is an invasive species that is also found in the United States and Canada, where it is not native. Eliminating this species of thistle is quite hard since its taproots are very long. It blooms from July through September, attracting wildlife. You can identify Scottish thistle by its purple blooms and thick, spikes leaf hairs. Flower buds can be cooked and eaten boiled similar to asparagus or rhubarb.

Spear Thistle (Cirsium vulgare)

Spear thistle is also known as bull thistle or common thistle. This species of thistle is probably the true Scottish thistle since it is abundant in that country and is native to most of the United Kingdom. Its roots are edible, cooked similar to Jerusalem artichoke, as well as the flower buds. Dried flowers are used as a substitute for rennet in cheese making. This plant is considered a weed so eating it is a great way of controlling the problem. Spear thistle help maintain natural biodiversity, since it is beneficial for wildlife.

Globe Thistle (Echinops ritro) 

This cousin of Scottish thistle is a non-invasive species which is ideal for floral gardens. Globe thistles are a hardy perennial that require little care as they are drought resistant. They can be grown in USDA zones 3 through 9. Silvery stems grow between 2 to 4 feet in height with violet or deep blue flower orbs which are loved by butterflies, bees and ladybugs.

Musk Thistle (Carduus nutans)

This type of thistle is commonly found throughout the United Kingdom, especially in England and Wales. It likes living in chalky soils, so you can plant it if you have this type of soil. Grow it in the less tended part of your garden. Musk thistle usually lives in rough grasslands or roadside verges.

Blessed Thistle (Carduus or Cnicus Benedictus)

Blessed thistle is native to the Mediterranean, from Portugal to France and even as east as Iran. It is an annual plant that grows up to 23 inches (60 centimeters) in height. This type of thistle has leathery, hairy leaves that are quite long, with small spines on the margins. Dense flowers are yellow in color.

This species of thistle has been used medicinally to stimulate the secretion of saliva and gastric juices. It increases appetite, facilitates digestion and stimulates the flow of bile. Buy blessed thistle supplements here.

Milk Thistle (Silybum marianum)

Milk thistle is known for its medicinal benefits, as it is a powerful anti-viral, anti-oxidant and has anti-inflammatory properties. Its main component – silymarin – is used to protect the liver from environmental toxins. It can also prevent and treat cancer, as well as enhance milk production in lactating mothers. Medicinal properties come from the seeds, which can be taken in a tea form, as well as capsules or tincture. Buy milk thistle supplements here.

Native to Europe and Asia, this plant is now found in North America. Milk thistle is an invasive species, so be careful not to allow seeds to spread. This plant grows quickly, up to 5 feet tall and 4 feet wide. It is very tolerant of any type of soil, including poor to medium fertility. Ideally, soil should be well drained with a neutral or middle alkaline pH. Milk thistle can tolerate frost and grows best in full sun.

Giant Cotton Thistle (Onopordum acanthium)

Giant Cotton Thistle is on the list of invasive species of thistle. It is important to cut its flower heads after flowering to prevent the seeds from scattering with the wind. Use strong gardening gloves when handling this plant since it is covered in spikes.

Reaching 10 to 15 feet in height and spreading 5 feet wide, this is the largest species of thistle. Therefore, it should not be planted in small gardens. Stony soil can help support its roots. Stalking is another good alternative to give support to this plant. Giant Cotton Thistle was used during the Middle Ages for its herbal properties. Poor people used its fluffy “down” to stuff mattresses.

Plume Thistle (Cirsium rivulare ‘Atropurpureum’)

Some species of thistle don’t have spikes such as the ornamental plume thistle which has beautiful magenta flower heads on top of long stems. Cut the plant after the first summer flowers bloom to promote another flowering. Chop the plant to the ground after the last bloom in fall to help it survive the winter.

Rivulare means “growing by a stream” which is appropriate, as this perennial prefers moist, yet well drained soil that is slightly acidic. Plume Thistle grows best in full sun. This is a popular ornamental flower in Europe, but pretty rare in America.

Russian Thistle (Echinops exaltatus)

This plant is native to Eurasia and is considered an invasive species of thistle in Canada and the United States. Russian thistle is also known as kali tragus (formerly classified as Salsola). This weed is known as “tumbleweed” which is what you see in the cowboy movies filmed in the American West. This plant propagates and produces seeds, then dries breaking loose from the desert soil. It rolls around continuing its growth cycle by spreading seeds. Plant crops so Russian thistle doesn’t find places to root or pull young plants to keep control.

Canada thistle (Cirsium arvense)

This perennial thistle has been a problem for American farmers since the European settlement. It is considered a weed that spreads vigorously, spreading its seeds by the wind. A creeping root system can increase the size of your patch from 6 to 10 feet in a season. A single plant can turn into a patch containing thousands of stems. Make sure to keep this plant in check since it can have a negative impact on wildlife.

Canada thistle is often mistaken with other species of thistle including bull thistle, musk thistle and plumeless thistle. All of these are biennial plants and reproduce only by seeds, since they have a strong single taproot. Canada thistle grows in patches and has small flowers, with smooth stems between the leaves.

Globe Artichokes (Cynara cardunculus)

Did you know artichokes are a species of thistle? Cynara includes Cynara cardunculus var. scolymus which is artichoke and cardoon, usually called artichoke thistle which is part of the sunflower family.

Cardoon is a herbaceous perennial plant that grows between 2 to 5 feet in height. It has green to gray-green leaves that are heavily spiked and can grow up to 20 inches (50 centimeters) long. Leaf stems are edible. Large globe flowers are violet-purple. It is native to the Mediterranean, from Morocco and Libya in Africa to Portugal, Greece and Croatia in Europe. Cardoon is considered a weed in California and Australia.

Artichoke is also known as French artichoke or green artichoke in the United States. This species of thistle is cultivated as food. Flower buds are edible before the plant blooms. After it blooms the structure changes to a coarse form, which is barely edible. Artichoke grows between 4 and 6 feet in height with silvery green leaves. This plant is one of the best vegetable sources of antioxidants.