Cotton thistle
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The Cotton thistle (Onopordum acanthium), also known as Scotch thistle or Scotch Cottonthistle, is a flowering plant from the sunflower family (Asteraceae).
The botanical name is derived from the Greek words onos (donkey), perdo (to consume), and acanthos (thorn), meaning 'thorny plant eaten by donkeys'.
The plant got its common name "Scotch thistle" from a legend the plant's thorny thickets helped protect Scotland from Viking attack. Oral folklore holds that as Vikings tried to sneak up at night to attack and raid Scot villages, they'd be stuck by the thistle's thorns and cry out in pain, alerting the townsfolk to the attack and allowing them to fight back and drive out the invaders.
It is a vigorous, biennial woody plant (sometimes annual), native to Europe, North Africa and Asia. In the late 19th century, it was introduced to much of mid-latitudes North America and temperate Australia as an ornamental plant.
Onopordon_acanthium.jpg
It prefers habitats with dry summers, such as the Mediterranean, growing in sandy, sandy clay and calcareous soils, rich in ammonium salts. It grows in ruderal places, as well as dry pastures, disturbed fields and range land. It is considered a noxious weed, difficult to eradicate because of its drought resistance. It can spread rapidly and in the end dense stands prohibits foraging by livestock.
The robust, spiny stem is covered with an arachnoid, white pubescence. It grows, at a slow rate, to a height of 0.5-2.5 m and a width of 1.5 m from a stout, fleshy taproot, that may extend down 30 cm or more . It is branched in the upper part. The massive, main stem may be 10 cm wide at the base. Each stem shows a vertical rows of broad, spiny wings (conspicuous ribbon-like leafy material), typically 2-3 cm wide, extending to the base of the flower head.
Cotton thistle is a biennial plant producing a rosette in the first season. Early in the second year, the plant bolts and produces flowers and seed.
The simple leaves are alternate and reticulate (net-veined) with pinnate main vein. In early rosettes, the leaves are oval in outline, shallowly lobed, and light green, with leaves up to 40 cm long and 15 cm wide. In mature stage, the lower leaves are elliptic and about 60 cm long by 30 cm wide. They are coarsely lobed with sharp, yellow, spiny-tipped margins. The leaves are covered with a light, velvety, gray mat and a white hairy undersurface. When the leaf hairs grow more thicker, the foliage progressively becomes more gray-green in color. The upper leaves are smaller with irregular toothed margins.
The flower buds form first at the tip of the stem and later at the tip of the axillary branches. The terminal flower heads are flat-topped corymb-like groups of 2 or 3 on the branch tips. They are globe-shaped and consists of only reddish-purple to violet disc florets with both pistil and stamens. This means they are androgynous. The mature flower heads are rather large, 3-4 cm wide. They sit above numerous, long, stiff, spine-tipped bracts, all pointing outwards, the lower ones wider apart and pointing downwards. They flower in mid-summer, from July to September.
After flowering, the hypogynous ovary starts swelling and forms about 8,400 to 40,000 seeds per plant. These slender and smooth achenes are about 3 mm long and are brown with gray markings. They are tipped with a pappus of slender bristles. They are mainly locally dispersed by wind. But humans, birds, wildlife, livestock and water may spread it to longer distances.
In the ground, seeds can remain dormant and viable for a long period, probably more than 20 years. Seeds are sensitive to light and only germinate when close to the surface. Seeds that germinate in late fall become biennials. But when they germinate earlier, they behave as annuals.
Uses
It may be sometimes be sold as an ornamental plant, but its edible and economic uses used to be more widespread.
The cooked receptacle or flower buds were used in earlier times as a substitute for the globe artichoke. The petals are an adulterant for saffron. The achenes contain about 25% oil, from which a good quality edible oil for burning and cooking can be obtained. The leaf juice is used by herbalists.
Scotch thistle is the national emblem of Scotland, dating from the time of James III of Scotland. The thistle is also part of the logo of Encyclopædia Britannica.
References and external links
- Grieve, M. 1971. A Modern Herbal: The Medicinal, Culinary, Cosmetic and economic Properties, Cultivation and Folk-Lore of Herbs, Grasses, Fungi, Shrubs & Trees with Their Modern Scientific Uses. Dover Publications, Inc., New York.
- Mucina, L. 1989. Syntaxonomy of the Onopordum acanthium communities in temperate and continental Europe. Vegetatio 81:107-115.
- Tucci, G., M.C. Simeone, C. Gregori, and F. Maggini. 1994. Intergenic spacers of rRNA genes in three species of the Cynareae (Asteraceae). Plant Systematics and Evolution 190:187-193.
- Washington state guide to the Scotch thistle (http://www.nwcb.wa.gov/weed_info/scotchthistle.html)
- Emblem of Scotland (http://www.killerplants.com/plants-that-changed-history/20030304.asp)