Species of the day: Garlic Mustard

, 04 May 2020
Species of the day: Garlic Mustard
Garlic Mustard © James Duncan

By James Duncan

Learning & Engagement Officer

The naming of Garlic Mustard (Alliaria petiolata) is technically a little misleading, at least in a botanical sense, for it bears no relation to the true garlics (Allium). It does, however, share one very distinct characteristic - it smells just like them. This is in fact a unique attribute for it's the one and only member of the mustard (Brassicaceae) family, or indeed any family other than the garlics, that has this trait. Though native in Britain, it's a widespread species, its distribution stretching all the way to both North Africa and central Asia. It's a ubiquitous plant, growing vigorously to more than a metre in moist shaded soils, for it's not a fan of the sun's full glare. 

Garlic Mustard has a couple of widely used colloquial names, 'Jack-by-the-hedge' and 'Hedge Garlic', both of which point accurately to its favoured habitat, though it also grows prolifically on waste and disturbed ground. It's a colonial species and where there's one plant, there's usually many. Interestingly it's typically a biennial species, requiring two years to complete its full biological life cycle, differentiating it from shorter lived annuals and longer-lived perennials. It's only during its second year that flowers and seed are produced - it exists purely as a low-lying rosette of leaves during its first. The elongated older leaves are toothed and look surprisingly like those of Common Nettle (Urtica dioica). The flowers are produced in small clusters and have four petals, arranged in the shape of a crucifix, giving the family its alternative name, the Crucifers (Cruciferae).

While the crushed leaves give off a pungent garlic aroma, the scent from the flowers isn't quite as captivating, attracting predominantly midges and hoverflies. However, Garlic Mustard isn't wholly reliant on insects as it is able to self-fertilise. Although a good number of insect herbivores are associated with Garlic Mustard, its most famous relationship exists with that of the Orange-tip Butterfly. The eggs laid by the Orange-tip eventually turn a conspicuous orange prior to typically hatching in June. The caterpillars will moult four times (instars) whilst actively feeding on the seed-pods, eventually pupating after three to four weeks. It isn't the only butterfly reliant on the plant, for the Green-veined White also favours Garlic Mustard for its developing larvae. Fortunately for both, they aren't in competition as the White eats the leaves instead.

Garlic Mustard has had a tremendous variety of traditional uses over the ages. Evidence for its herbal use in Europe may date back more than 6000 years. More recently, in the seventeenth century, it was widely used as a flavouring for salted fish and meat and as an addition to sauces and salads. It was in fact so well liked by Europeans that early settlers introduced it to North America, where it's now considered to be an invasive species. Even today its nutritional properties help it to remain a commonly foraged plant that serves a variety of culinary purposes. 

Garlic Mustard3

Garlic Mustard2

Garlic Mustard © James Duncan

Leave a comment