Cotton Thistle

onopordum acanthium

The Cotton Thistle is a majestic and imposing biennial plant renowned for its striking silver-grey appearance and formidable array of thorns. Standing tall as a member of the sunflower family (Asteraceae), it has a rich history and was traditionally chosen as the national emblem of Scotland. It is highly valued in gardens for its dramatic, architectural presence, although in many parts of North America and Australia, it has earned a reputation as an aggressive, invasive weed due to its rapid spreading tendencies in disturbed soils.

Habitat: Typically found in disturbed areas, dry pastures, roadsides, waste places, and dry fields with sandy or gravelly soils.

Appearance

This tall, branching biennial can reach heights between 50 to 300 centimeters. Its entire structure is covered in a dense, woolly webbing of white-to-grey hairs, giving the plant a distinctive dusty or cottony appearance. The sturdy stems feature broad, spiny, running wings along their length. Its leaves are large, coarse, and deeply lobed with sharp yellow spines at the margins, while the flower heads are globe-shaped, 3 to 5 centimeters wide, and capped with vibrant purple-to-pink florets surrounded by spine-tipped bracts.

KingdomPlantaePhylumTracheophytaClassMagnoliopsidaOrderAsteralesFamilyAsteraceaeGenusOnopordum

Cotton Thistle

Interesting facts

Its scientific name Onopordum translates roughly from Greek to 'donkey flatulence,' originating from an ancient belief that eating the plant caused gas in donkeys.

The Cotton Thistle is the traditional national emblem of Scotland, symbolizing fierce defense due to its painfully sharp spines.

The seeds contain up to 25 percent oil, which was historically extracted and burned in lamps across Europe.

Special abilities

The entire plant is heavily armored with sharp spines along its stems and leaf margins, which effectively deter large herbivores from grazing on its foliage.

A dense covering of white, cottony trichomes reflects excess solar radiation, reduces water loss through transpiration, and protects the plant from harsh, drying winds.

A single plant can produce tens of thousands of seeds that remain viable in the soil seed bank for several years, waiting for optimal germinating conditions.

Measurements & details

Length: 50-300 cm
Weight: 0.1-2 kg
Lifespan: 2 years

Diet & Feeding

As an autotrophic plant, the Cotton Thistle produces its own food through photosynthesis, utilizing sunlight, water, carbon dioxide, and soil minerals.

Primary Foods

Sunlight
Water
Carbon dioxide
Soil nutrients

Ecological connections

mutualism

Western Honey Bee

Apis mellifera

Provides abundant nectar and pollen for foraging workers.

host plant

Painted Lady

Vanessa cardui

Caterpillars feed on the spiny leaves as their primary host plant.

eaten by

European Goldfinch

Carduelis carduelis

Adult birds feed on the protein-rich seeds during autumn.

Traits

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Also known as

No aliases listed yet.

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Safety

Danger

1/5 · Very low

No special safety notes yet.

Frequently Asked Questions

How to identify Cotton Thistle?

The easiest way to identify Cotton Thistle is to use the Snappit nature identifier app.

How long is Cotton Thistle?

50-300 cm

How much does Cotton Thistle weigh?

0.1-2 kg

How long does Cotton Thistle live?

2 years

What does Cotton Thistle eat?

As an autotrophic plant, the Cotton Thistle produces its own food through photosynthesis, utilizing sunlight, water, carbon dioxide, and soil minerals.

Where is Cotton Thistle usually found?

Typically found in disturbed areas, dry pastures, roadsides, waste places, and dry fields with sandy or gravelly soils.