Cirsium vulgare is a biennial herbaceous plant that is considered a noxious weed in many parts of the world. It reproduces by seeds. The stems are tall, branching, and spiny, about 0.9-2m tall.
It is easily recognized by the stiff spines on the stems and leaves and pink to purple tubular flowers surrounded by spine-tipped bracts.
Bull Thistle Classification
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Asterales
- Family: Asteraceae
- Genus: Cirsium
- Species: Cirsium vulgare
- Varieties: Cirsium vulgare var. litorale
- Common Names: Common thistle, Bur thistle, Bird thistle, Button thistle, Blue thistle, Black thistle, Spear thistle, Scotch thistle, and Bank thistle.
Nativity and Distribution
Bull thistle is native to Europe, Western Asia, and Northern Africa. Today, it can also be found in:
- North America
- South America
- South Africa
- Australia
- New Zealand
Physical Characteristics
- Leaves: Elliptical basal leaves and lance-shaped stem leaves
- Fruits: Small achenes 5 mm long with feathery pappus
- Stems: Erect, spiny, branching, green stems
- Flowers: Solitary purple flower surrounded by spiny bracts
- Roots: Tap root system
Cirsium vulgare is a biennial and occasionally a perennial herbaceous plant 90-210 cm tall. It is recognizable by the stiff spines on the stems and leaves and purple tubular flowers surrounded by spine-tipped bracts.
The stems are winged, branched, spiny, about 90-210 cm, and covered in dense hairs. Bull thistle produces two sets of leaves in its two-year life cycle.
In the first year, it produces deeply lobed, spiny basal rosette leaves about 65 cm wide. In the second year, the stem bolts up to about 2 metres with lanceolate and alternate leaves. The upper leaves, about 30 cm long, have stiff spines on the edges, stiff hairs on the upper side, and soft white hairs on the underside.
Bull thistle produces purple flower heads that develop on the apex of the stem. They can be solitary or in groups of 2-3 flowerheads. The flower head is 2.5 cm long and 3-5 cm wide and has several disc florets. Each flower is surrounded by stiff narrow bracts with yellow tips.
The seeds are oblong, straw-coloured, about 2.5-5 mm long with feather-like bristles at the tip.
Reproduction, Dispersal, and Life Cycle
- Life Cycle: Biennial
- Seeds: A single plant can produce between 5,000 to 50,000 seeds
- Climate: Temperate and warm-temperate subtropical climate zones
- Dispersal: Animals, wind, and contaminated machinery or produce
Bull thistle behaves mainly as a biennial, thriving in sunny open areas. It is a prolific seed producer with a single flower head producing about 40-300 seeds. A single plant produces a minimum of 5,000 seeds with the vigorous types producing close to 50,000 seeds.
Most of the seeds produced are dispersed near the parent plant and hence the dense weed infestations typically witnessed in most affected areas. A smaller percentage of the seeds are moved by wind, animals, vehicles, and farming equipment, and contaminated produce like crop seeds and hay.
Bull thistle seeds have a high germination rate of 95% on shallow soil and up to 1-2 inches beneath the soil surface. Seeds buried at a depth of 5 inches may remain viable for three years.
Similar Plants
- Cirsium undulatum
- Cirsium flodmanii
- Cirsium arvense
- Cirsium brevistylum
- Silybum marianum
Uses
- Young leaves and shoots harvested in the early stages can be consumed in salads and the young stems and roots as cooked vegetables.
- It is a high-value nectar plant for the honey industry.
- It was used as a medicinal plant for haemorrhoids, poor digestion, and rheumatic joints.
Impact on Farms and Environment
While C. vulgare is an important nectar plant and food source for a variety of bees, butterflies, and birds, it is also a serious weed in agricultural farms. It competes for important resources, reducing the quantity of yield for grain and horticultural produce.
The spiny nature of the weed also reduces the quality of produce for products like hay, grain, and wool, leading to economic losses.
As a weed of pastures, bull thistle reduces grazing areas, inhibits livestock movement, and causes injury.
Due to its prolific seed production and high infestation rate, it can quickly dominate areas and outcompete native vegetation. Bull thistle can grow in a variety of soils and weather conditions.
It is mostly found in forest verges, tree plantations, riparian areas, pastures, roadsides, and other disturbed areas.
Cirsium vulgare can also harm human beings. In case of contact with rosettes or mature plants, it can cause contact dermatitis or puncture wounds.
When located on roadsides, large plants may decrease visibility and potentially lead to dangerous road accidents. Bull thistle plants are imposing and may also impede movement to areas where they border.
Control
- Cultural control: Grazing control and good turf management
- Mechanical control: Hand pulling, mowing, tillage, and cutting
- Chemical control: Herbicides like 2,4-D, Dicamba, and aminopyralid
The best control measure for bull thistle is prevention. Avoid soil and hay from other areas that may spread the weed on your property.
If a small infestation has already occurred, hand-pulling and tillage can help control the spread, but only if done before the reproduction stages. Repeated mowing and slashing can also be effective if done before flowering.
Grazing management (moving animals from area to area in a planned sequence) combined with planting competitive and vigorous pastures has also been shown to limit the establishment of the weed.
For larger infestations, chemical herbicides may be the best control measure. The herbicides indicated for bull thistle include 2,4-D, Dicamba, aminopyralid, picloram, MCPA, and glyphosate. Apply to the rosettes in autumn or the spring before they bolt.
Many biological agents including weevils like Trichosirocalus horridus and fungus Sclerotinia sclerotiorum have been applied for Cirsium vulgare with little success.
Lead Editor for Insight Weeds.