Wild rhubarb (Arctium minus) is a large and bushy biennial flowering plant that reproduces sexually through seeds. It is erect-growing and can reach up to 1.8m tall while forming several branches.
The plant can be easily identified by its pink to purple flowers enclosed in a bur with several prickly bracts.
Wild Rhubarb (Arctium minus) Scientific Classification
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Tracheophyta
- Subphylum: Angiospermae
- Class: Magnoliopsida
- Order: Asterales
- Family: Asteraceae
- Genus: Arctium
- Species: Arctium minus
- Common Names: Common burdock, lesser burdock, button-bur, louse-bur, cuckoo-button, and wild burdock.
Nativity & Distribution
Arctium minus is native to Europe. However, it is widely distributed in several regions worldwide, including:
- North America
- Asia
- South America
- Australia
- New Zealand
Physical Characteristics
- Leaves: Large, heart-shaped, alternate leaves.
- Fruits: Sticky burs with prickly hooks.
- Stems: Stout, grooved stem that is hollow inside and forms multiple branches.
- Flowers: Pink to purple flowerheads covered by bracts with prickly spines.
- Roots: Large, thick, branching taproot.
Wild rhubarb is an erect-growing, bushy, and branching biennial plant that can reach 1.8m in height. You can easily recognize the plant by its purplish flowerheads with hooked and spiny bracts.
In its first year of growth, it produces dark-green rosette leaves, which are large (up to 60cm long and 30cm wide), heart-shaped, and with a hairy undersurface. The rosette leaves have a hollow stalk (petiole), rounded at the tip, and with wavy, toothless, or finely toothed margins.
In its second year of growth, the plant develops single, stout (but brittle) branching stems that are green to reddish purple and can be slightly hairy or hairless.
New leaves form alternately along the stem, becoming smaller and short-stalked as they ascend. Therefore, upper leaves are usually stalkless and much smaller than the basal ones.
Arctium minus produces short-stalked, thistle-like flower heads at the tip of branches or leaf axils. Each flower head is about 1.5-5cm and has about 20-40 pink to purple (sometimes white) tubular flowers.
The flowers are in an egg-shaped bur with several green, spiny bracts.
Wild rhubarb produces flowers during its second year of growth, which bloom from around July to October.
Reproduction, Dispersal, & Life Cycle
- Life Cycle: Biennial
- Seeds: Can produce up to 15,000 seeds.
- Climate: Grows well in temperate climates that are warm and humid.
- Dispersal: Burs that stick to animals, birds, and clothes.
Flower heads mature into seed heads, with the spiny bracts becoming stiff. This enables them to attach to animal fur, birds, clothing, and anything else that passes, allowing for the wide dispersal of the entire seed head.
The seedhead contains tiny dark-brown to blackish seeds about 5-8mm long. At the top of the seeds is a cluster of small bristles (pappus hairs) about 1.5-3mm long, which fall off as the seed becomes dry.
Wild rhubarb reproduces sexually through seeds. A single plant can produce around 15,000 plants with a 90% germination rate.
Seeds germinate easily when they land on bare soil. In addition, seeds buried deep in the soil can remain viable for up to three years, during which time they can sprout new plants when the soil is disturbed.
Uses
- The leaf stalks, flower stalks, and roots of young plants are edible.
- It is used in Chinese and Western traditional medicine to treat various ailments.
- Fiber from the inner bark of the plant is used for making paper.
- Livestock may graze on the plant.
Impact on Farms and Environment
Wild rhubarb is an invasive weed that produces several seeds that can easily germinate into new plants. It also spreads very fast, with the burs sticking onto animals for several weeks, causing it to be dispersed as far as 10km from the mother plant.
It is an aggressive grass that spreads quickly through prolific seeding and rhizomatous roots. It also produces a phenolic compound that can inhibit the growth and survival of other plants.
In the newly invaded areas, the plant’s large leaves can reduce sunlight for shorter native vegetation, allowing it to outcompete them. The plant is also susceptible to root rot and powdery mildew, which can significantly affect surrounding agricultural plants.
The burs that stick on animals can damage their fur or, in the case of sheep, lower the quality and value of the wool. In addition, the burs can trap small birds and bats, killing them if they cannot untangle themselves.
While not toxic, the weed is considered harmful because it produces lactones that can cause skin irritation on contact in some people. The small bristles on the seeds are also easily windborne and can irritate the eyes, skin, and respiratory system.
Lastly, while animals can graze on the plant, excessive ingestion can taint the milk.
Control
- Natural methods: Hand-pulling, digging, cutting to the base, mowing, and cultivation.
- Chemical control: Chemical herbicides like 2,4-D, Metsulfuron, dicamba, glyphosate, and clopyralid.
The best way to control Arctium minus is through prevention. The plant mostly invades bare areas, so you can prevent infestation by planting ground cover crops or competitive, beneficial plants.
You can remove the weeds for already invaded areas by hand-pulling small infestations. However, this is only effective for young plants; you might need to dig deep to remove the entire tap root when dealing with mature plants.
You can also control wild rhubarb by mowing or cutting the plant to the stem. However, to avoid spreading the seeds, you should only do this before the flowers bloom.
In most cases, the weed will regrow after mowing or cutting, but repeated treatment can ultimately overwhelm it. You could also apply vinegar or other natural homemade weed killers to the cut stem, causing the tap root system to wither and die.
Cultivation can also work as a weed control method for wild rhubarb, but only if done before the plant flowers. However, this can also disturb any dormant seeds in the soil, leading to a flush of new germination.
Chemical herbicides are the most effective solution for controlling Arctium minus. You can use selective herbicides like 2,4-D, Metsulfuron, dicamba, and clopyralid in areas with other vegetation or broad-spectrum herbicides like glyphosate in bare areas.
Foliar spray is the best method of chemical application because of the plant’s large flowers. In some cases, repeated herbicide treatment may be necessary to completely eradicate the weed.
Lead Editor for Insight Weeds.