Alliaria petiolata (*)
Alliaria petiolata, (M.Bieb.) Cavara & Grande
* USDA, NRCS. 2006. The PLANTS Database, 6 March 2006 (http://plants.usda.gov).
Garlic mustard (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 attractive 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 hedgerows, giving rise to the old British folk name of Jack-by-the-hedge. Other common names include 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.
Lawrence Newcomb gives the species name Alliaria officinalis for this plant.
It is a herbaceous biennial plant (sometimes an annual plant) growing from a deeply growing, thin, white taproot that is scented like a horse-radish. 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. 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. 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. Some plants can flower and complete their life-cycle in the first year. 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. Garlic mustard has been classified as Magnoliopsida.
Cultivation and 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 and pesto. They were once used as medicine.
In Europe as many as 69 species of insects and 7 species of fungi utilize Garlic Mustard as a food plant, including the larvae of some Lepidoptera species such as the Garden Carpet moth.
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 and is listed as a noxious or restricted plant as of 2006 in the US states of Alabama, Connecticut, Massachusetts, Minnesota, New Hampshire, Oregon, Vermont, West Virginia and Washington. 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. It is a possible threat to the West Virginia White Butterfly (Pieris virginiensis) and Mustard White Butterfly (Pieris oleracea); adult butterflies of both species lay their eggs on native Dentaria or Toothwort plants, but they often confuse garlic mustard plants with Dentaria and lay their eggs on garlic mustard, because they have similar flowers. The eggs and young butterflies cannot live on the garlic mustard, because it has chemicals that are toxic to the larvae and eggs.
A study published in 2006 concluded that Garlic Mustard produces allelochemicals that harm mycorrhizal fungi that many North American plants, including native forest trees, require for optimum growth. 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. A complication to the eradication of Garlic Mustard from an area is the longevity of viable seeds in the ground. Seeds contained in the soil can germinate up to five years after being produced.
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.
1. ^ "Flora Europaea". Royal Botanic Garden Edinburgh. http://rbg-web2.rbge.org.uk/cgi-bin/nph-readbtree.pl/feout?FAMILY_XREF=&GENUS_XREF=Alliaria&SPECIES_XREF=&TAXON_NAME_XREF=&RANK=.
Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License