(M.Bieb.) Cavara & Grande
Alliaria petiolata is a biennial 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). In the first year of growth, plants form clumps of round shaped, slightly wrinkled leaves, that when crushed smell like garlic. The next year plants flower in spring, producing cross shaped white flowers in dense clusters. As the flowering stems bloom they elongate into a spike-like shape. When blooming is complete, plants produce upright fruits that release seeds in mid-summer. Plants are often found growing along the margins of hedges, giving rise to the old British folk name of Jack-by-the-hedge. Other common names include Garlic Mustard, Garlic Root, Hedge Garlic, Sauce-alone, Jack-in-the-bush, Penny Hedge and Poor Man's Mustard. The genus name Alliaria, "resembling Allium", refers to the garlic-like odour of the crushed foliage. Some people give the species name Alliaria officinalis for this plant.
In 17th century Britain it was recommended as a flavouring for salt fish. It can also be made into a sauce for eating with roast lamb or salad. All parts of the plant, including the roots, give off a strong odour. The small white flowers have a rather unpleasant aroma which attracts midges and hoverflies, although the flowers usually pollinate themselves. In June the pale green caterpillar of the orange tip butterfly (Anhocharis cardamines) can be found feeding on the long green seed-pods from which it can hardly be distinguished.
It is a herbaceous biennial plant growing from a deeply growing, thin, white taproot that is scented like horseradish. In the 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. Second year plants grow from 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 5–9 cm broad, with a coarsely toothed margin. The flowers are produced in spring and summer in button-like clusters. Each small flower has four white petals 4–8 mm long and 2–3 mm broad, arranged in a cross shape. The fruit is an erect, slender, four-sided pod 4 to 5.5 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. A single plant can produce hundreds of seeds, which scatter as much as several meters from the parent plant.
Depending upon conditions, garlic mustard flowers either self-fertilize or are cross-pollinated by a variety of insects. Self-fertilized seeds are genetically identical to the parent plant, enhancing its ability to colonize an area where that genotype is suited to thrive.
Cultivation and uses
Garlic mustard is one of the oldest discovered spices to be used in cooking in Europe. Evidence of its use has been found from archeological remains found in the Baltic, dating back to 6100-5750 BP.
The chopped leaves are used for flavoring in salads and sauces such as pesto, and sometimes the flowers and fruit are included as well. These are best when young, and provide a mild flavour of both garlic and mustard. The seeds are sometimes used to season food directly in France.
In Europe as many as 69 species of insects and seven species of fungus utilize Garlic Mustard as a food plant, including the larvae of some Lepidoptera species such as the Garden Carpet moth.; however, in North America, the plant offers no known wildlife benefits and is toxic to larvae of certain butterfly species that lay eggs on the plants, as it is related to native mustards.
As an invasive species
Garlic mustard was introduced in North America as a culinary herb in the 1860s and is an invasive species in much of North America. As of 2006[update], it is listed as a noxious or restricted plant in the US states of Alabama, Connecticut, Massachusetts, Minnesota, New Hampshire, Oregon, Vermont, West Virginia and Washington., and occurs in 27 midwestern and northeastern states in the US, and in Canada. Like most invasive plants, once it has an introduction into a new location, it persists and spreads into undisturbed plant communities. In many areas of its introduction in Eastern North America, it has become the dominant under-story species in woodland and flood plain environments, where eradication is difficult.
The insects and fungi that feed on it in its native habitat are not present in North America, increasing its seed productivity and allowing it to out-compete native plants.
Garlic Mustard produces allelochemicals, mainly in the form of the cyanide compounds allyl isothiocyanate and benzyl isothiocyanate, which suppress mycorrhizal fungi that most plants, including native forest trees, require for optimum growth. However, allelochemicals produced by Garlic Mustard do not affect mycorrhizal fungi from Garlic Mustard's native range, indicating that this "novel weapon" in the invaded range explains Garlic Mustard's success in North America. Additionally, because white-tailed deer rarely feed on Garlic Mustard, large deer populations may help to increase its population densities by consuming competing native plants. Trampling by browsing deer encourages additional seed growth by disturbing the soil. Seeds contained in the soil can germinate up to five years after being produced (and possibly more). The persistence of the seed bank and suppression of mycorrhizal fungi both complicate restoration of invaded areas because long-term removal is required to deplete the seed bank and allow recovery of mycorrhizae.
Garlic mustard produces a variety of secondary compounds including flavonoids, defense proteins, glycosides, and glucosinolates that reduce its palatability to herbivores. Research published in 2007 shows that, in northeastern forests, garlic mustard rosettes increased the rate of native leaf litter decomposition, increasing nutrient availability and possibly creating conditions favorable to garlic mustard's own spread.
Preventing seed production and depletion of the soil seed bank are key to eradicating infestations. Non chemical control includes removal by hand-pulling or cutting at the base; mowing; burning; or manipulation of the environment to reduce light. Pulling is more effective if the root is removed. Garlic mustard may invade forested sites where the canopy has been disturbed, so management by planting or encouraging other plants to intercept light will aid control, or prevent new infestations. Control is best in early spring before flowering. Removed plants should be bagged or burned, as seeds or roots may survive composting. Chemical control may be achieved by foliar application with a number of different herbicides. Timing herbicide applications to early spring or late fall may protect native or desirable plants in the same locations as Garlic mustard is generally active across a longer season than other plants in northern temperate climates. All methods of weed control must be repeated for 3–4 years or longer to be effective—as seeds germinate, or as surviving roots re-sprout the infestation may be quickly re-established.
- "Flora Europaea". Royal Botanic Garden Edinburgh.
- "BSBI List 2007" (xls). Botanical Society of Britain and Ireland. Retrieved 2014-10-17.
- Lawrence Newcomb (1977). Newcomb's Wildflower Guide. Boston: Little, Brown and Company. pp. 138–139.
- Reader's Digest Nature Lover's Library, Field Guide to the Wildflowers of Britain, Editor Michael W. Davison, Art Editor Neal V. Martin, The Reader's Digest Association Limited, 11 Westferry Circus, Canary Wharf, London E144HE, Reprint 2001, ISBN 0 276 42506 5
- "Invader of the Month - Garlic Mustard - Alliaria petiolata". Retrieved 2009-05-21.
- PCA Alien Plant Working Group - Garlic Mustard (Alliaria petiolata)
- Saul, Hayley; Madella M; Fischer A; Glykou A; Hartz S et al. (21 August 2013). "Phytoliths in Pottery Reveal the Use of Spice in European Prehistoric Cuisine". PLOS ONE (PLOS). doi:10.1371/journal.pone.0070583. ISSN 1932-6203. Retrieved 22 August 2013.
- Gualtiero Simonetti (1990). Stanley Schuler, ed. Simon & Schuster's Guide to Herbs and Spices. Simon & Schuster, Inc. ISBN 0-671-73489-X.
- "Plants For A Future: Database Search Results". Retrieved 2009-05-16.
-  Pest Management Invasive Plant Control - Garlic Mustard (Alliara petiolata) USDA NRCS Conservation Practice Job Sheet MN-797
- plants.usda.gov/java/profile?symbol=alpe4; PLANTS Profile for Alliaria petiolata (garlic mustard) | USDA PLANTS]
-  Minnesota Department of Natural Resources website
- Luken, James O., and John W. Thieret. 1997. Assessment and management of plant invasions. Springer series on environmental management. New York: Springer. ISBN 978-0-387-94809-6 Page 117.
- Journal of Chemical Ecology, November 1999, Volume 25, Issue 11, pp 2495-2504
- Stinson KA, Campbell SA, Powell JR, Wolfe BE, Callaway RM et al. (2006). "Invasive Plant Suppresses the Growth of Native Tree Seedlings by Disrupting Belowground Mutualisms". PLoS Biology 4 (5): e140. doi:10.1371/journal.pbio.0040140. PMC 1440938. PMID 16623597. Retrieved 2007-05-24.
- Callaway RM et al. 2008. Novel weapons: Invasive plant suppresses fungal mutualists in America but not in its native Europe. Ecology 89:1043-1055
- Garlic Mustard. Plant Conservation Alliance Alien Working Group. Accessed on 14 July 2007. 
- Anderson RC, Anderson MR, Bauer JT, Slater M, Herold JM, Baumhardt VA. 2010. Effect of removal of garlic mustard (Alliaria petiolata Brassicaceae) on Arbuscular Mycorrhizal Fungi inoculum potential in forest soils. Open Ecology Journal 3:41-47 http://www.benthamscience.com/open/toecolj/articles/V003/41TOECOLJ.pdf
- Isovitexin 6″-O-β-d-glucopyranoside: A feeding deterrent to Pieris napi oleracea from Alliaria petiolata. Meena Haribal and J. Alan A. Renwick, Phytochemistry, Volume 47, Issue 7, April 1998, Pages 1237-1240, doi:10.1016/S0031-9422(97)00740-1
- Daxenbichler ME, Spencer GF, Carlson DG, Rose GB, Brinker AM, Powell RG. 1991.Glucosinolate composition of seeds from297 species of wild plants. Phytochemistry 30: 2623–2638.
- CipolliniD. 2002.Variation in the expression of chemical defenses in Alliaria petiolata (Brassicaceae) in the field and common garden. American Journal of Botany 89: 1422–1430.
- Vikki L. Rodgers, Benjamin E. Wolfe, Leland K. Werden1 and Adrien C. Finzi (2008). "The invasive species Alliaria petiolata (garlic mustard) increases soil nutrient availability in northern hardwood-conifer forests". Oecologia 157 (3): 459–71. doi:10.1007/s00442-008-1089-8. PMID 18612654.
-  University of Wisconsin Extension, Management of invasive plants in Wisconsin: Garlic mustard (A3924-07)
|Wikimedia Commons has media related to Alliaria petiolata.|
|Wikiversity has bloom time data for Alliaria petiolata on the Bloom Clock|
|Wikisource has the text of a 1911 Encyclopædia Britannica article about Alliaria petiolata.|
- 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
- Species Profile- Garlic Mustard (Alliaria petiolata), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Garlic Mustard.
- Most Unwanted - Garlic Mustard (Alliaria petiolata), Ontario Invasive Plant Council. Biological information and resources for Garlic Mustard in Ontario.