Alliaria petiolata

Alliaria petiolata

Garlic Mustard
Binomial:	Alliaria petiolata
Family:	Brassicaceae
Type:	Biennial
Light requirements:	Sun to dense shade
Weediness:	Very weedy
Seed Dispersal:	Explosive capsules, easily transported by foot traffic
Germination Time:	Late summer to early autumn
Seed Banking:	Long-term
Allelopathy:	allelopathic to mychorrizal fungi
Height and spread:	30-100 cm tall
Toxicity and edibility:	edible, tasting like garlic and mustard

Garlic mustard or Hedge garlic (Alliaria petiolata) is a flowering plant in the Mustard family, Brassicaceae. It is native to Europe, western and central Asia, and northwestern Africa, from Morocco, Iberia and the British Isles, north to northern Scandinavia, and east to northern India and western China (Xinjiang). It often occurs along the margins of hedgerows, giving rise to the old British folk name of "Jack-by-the-hedge". The genus name Alliaria, "resembling Allium", refers to the garlic-like odour of the crushed foliage.

Description

It is a herbaceous biennial plant (sometimes an annual plant) growing to 30–100 cm (rarely to 130 cm) tall. The leaves are stalked, triangular to heart-shaped, 10–15 cm long (of which about half being the petiole) and 2–6 cm broad, with a coarsely toothed margin. In biennial specimens, first-year plants appear as a rosette of green leaves close to the ground; these rosettes remain green through the winter and develop into mature flowering plants the following spring. Others flower and complete their life-cycle in their first year. The flowers are produced in spring and summer in buttonlike clusters, each flower small, white, with four petals 4–8 mm long and 2–3 mm broad, in the shape of a cross. The fruit is an erect, slender, four-sided pod 2–7 cm long, called a silique, green maturing pale grey-brown, containing two rows of small shiny black seeds which are released when the pod splits open.

Close-up of Garlic Mustard flowers

A single plant can produce hundreds of seeds, which scatter as much as several metres from the parent plant. Depending upon conditions, garlic mustard flowers either self-fertilise or are cross-pollinated by a variety of insects. Self-fertilised seed is genetically identical to the parent plant, enhancing its ability to colonise an area. Although water may transport the seeds, they do not float well and are not carried far by wind. Long distance dispersal is most likely aided by human activities and wildlife.

Ecology

In Europe as many as 69 species of insects and 7 species of fungi utilise Garlic Mustard as a food plant, including the larvae of some Lepidoptera species such as the Garden carpet moth.

Garlic mustard was introduced in North America as a culinary herb in the 1860s and is considered an invasive species there. The insects and fungi that feed on it in natural conditions are not present in North America, increasing its seed productivity and allowing it to out-compete native plants there. In addition, a study published in 2006 concluded that Garlic Mustard harms mycorrhizal fungi that some North American plants, including native forest trees, require for proper growth. Additionally, because White-tailed Deer rarely eat Garlic Mustard, large deer populations may help to expand it by removing competing native plants and exposing the soil and seedbed through trampling. A complication in the eradication of Garlic Mustard is the long time span in which seeds may remain viable in the ground for. Seeds have been observed to germinate up to 11 years after being planted in the ground.

Uses

The leaves, flowers and fruit are edible as food for humans, and are best when young. They have a mild flavour of both garlic and mustard, and are used in salads.

Similar Plants

In the rosette stage it can be easily confused with Brunnera macrophylla or sometimes Glechome hederacea or Asarum canadensis.

Control

• Mowing: Mowing is effective if done on a regular basis
• Cultivation: effective against seeding, though the seed bank means repeated cultivations will be needed
• Mulching (for prevention): thick mulches will prevent germination in the fall
• Pulling: Pulling is effective, though care must be taken to pull before the seeds are ripe. Explosive capsules may be triggered by pulling, and the seeds can easily be transported on shoes or clothing.
• Flame: Flameweeding is effective on young plants
• Disposal: Hot composting only if seeds are present

References

• Flora Europaea: Alliaria petiolata
• Flora of China: Alliaria petiolata
• Flora of Pakistan: Alliaria petiolata
• Plants for a Future: Alliaria petiolata
• Garlic mustard recipes
• U.S. NPS guide