Some plants struggle for survival and are rarities we come across only seasonally, some are common and perennial, while others can be found all year long and form boring monocultures. These latter species may use a form of chemical warfare called allelopathy (Gr: allelon = shared, pathos=suffering) by producing plant toxins which inhibit growth of neighboring plants and encourage nearly pure stands of only one species (a monoculture). Garlic Mustard is one of these species.
On my daily walks this fall I observed the slow but steady progression of season foliage colors from deep green to yellow, to red and finally, to dull and dry muted browns and grays. By mid-December after several wind storms, most leaves—brown and crinkly-had fallen during the past week to carpet the ground. So, on this day, against a bright blue sky, the fall of a single brown leaf, tumbling and gliding downward caught my eye. It came from thee top of a 60 foot White Oak tree (Quercus alba). It floated with its dried up leaf-lobes curled up like ailerons on an airplane—floating toward my path.
I imagined its origin up on the tree-top where its dry and brittle petiole, finally broke away to release this captive leaf to permit a gentle fall to earth. It sailed down and down. twisting left and right, banking this way and that on a glide path controlled by the day’s wind gusts to drift right past me—-just out of reach—and settle like a brown visitor onto the only patch of bright greenery which spread out in an elongate patch under the boughs of trees at that season bereft of leaves.
This unseasonal patch of greenery, composed of only one species—is a common invasive weed called Garlic Mustard (Alliaria petiolata). Its monospecific stand of individuals of only one species often dominate shady areas under brush or trees or in disturbed forests or waste places. The British common term for this species of the mustard family is Jack by the Hedge or Hedge Garlic which is an appropriate term for in the shade of hedges and hedgerows so common surrounding British farm fields for that is the area where this species is most commonly found. And under that hedge if you see one Garlic Mustard plant— it is never alone, always in company with many of its own species.*
With the entire floral world having long given up their green to accommodate the lowering sun and falling temperatures, this ground-hugging, Jack by the Hedge, Hedge Garlic, or Poorman’s Mustard a member of the Crucifer or Brassicacea family which includes cold tolerant vegetables rich in vitamins and minerals such as broccoli, kale, cauliflower and cabbage. The old term Crucifera “cross bearing” was a reference to its simple white flowers with four petals arranged in a cross pattern. The family includes cabbage, kale, broccoli, radish, and turnips as well as mustards of various species. The Garlic Mustard braves chill days and sub freezing nights to stay lively and verdant well into fall and early winter and in spring is the first to flourish.
During its first year Garlic Mustard produces a low growing rosette of rounded leaves which is followed in its second year as a tall plant with a single rising stem topped with a cluster of white, cross-bearing simple flowers. The leaf of the first-year plant can be described as having a “colts-hoof” shape and grows in densely packed clumps which hug the ground and may help it conserve moisture and limit exposure to the chill air of the fall season. Alliaria patches dominate many southern exposed patches of earth along my walking path. They are a pleasant sight of green among the brown, wind-bent grasses and dead spent brown crinkly dry fallen leaves.
Garlic Mustard is a biennial plant (having a two year life cycle—in which its leaves and roots sprout up in the first year, then when grown up enough to reproduce flowers and seeds it sprouts up the next year in a new reproductive form. . Its rounded first season leaves—like a colt’s hoof-print—are deeply veined and have scalloped edges. The leaves measure (here on Long Island) 2-3 inches across.. Its small white four-petaled, cross shaped, simple flowers are typical of this family. The white crucifera flowers arise on the plant in its second year of growth as rounded clusters at the top of long stems. When crushed or bruised Garlic Mustard leaves and stems give off a distinctive “garlic” fragrance. Its binomial scientific name arise from this fact. Alliaria petiolata is derived from Latin. The genera: Alliaria means “garlic”, while petiolata from Latin is a term for ‘stalked’. The latter is a reference to its long flowering stem which sprouts during its second season of growth which likely supports its seed dispersal prospects.
Native to Europe and the British Isles, Garlic Mustard is found as far north as Scandinavia, and south to northwestern Africa and east to western Asia, Pakistan and western China. Its old world distribution suggests the family evolved during the early to mid Cenozoic Era ( @ 66 mya-30mya) after the split up of the supercontinent Laurasia, The proliferation of its seeds and modern transportation left little chance that this species would not be introduced into North America, and the plant was first observed in the USA in 1861 and reported on Long Island by 1868. Today it is a very common weed plant found widely over all of the Northeast and the contiguous USA.
The leaves of the second year plant arise at alternate positions on the stem, are pointed or heart shaped, and are coarsely toothed. The second year plant grows a tall upright stem with, as noted above, clusters of white flowers at its top, very much unlike the rosette of ground hugging colt-hoof shaped leaves of its first year.
The second year or spring plant’s stems sprout to 10-12 inches in early spring and may grow to a meter high by the summer.They produce small clusters of typical crossifera type, four-petaled white flowers. They can not self pollinate. So the flowers with its sticky pollen is typically pollinated by bees. Bumble bees are the most common visitors and pollinators of this species. The fruit is an upright capsule (silique) which produces small black seeds. When the capsule dries it splits open to release about twenty tiny black mustard seeds. Since each plant can produce many siliques, a single plant can produce between 600 to 8,000 seeds in its second season. The seeds are launched into the air when the silique opens explosively and being very tiny can be launched as far away as 10 feet (about 3 meters). So they are formidable seed producers and dispersers.
A petiolata is native to Europe and Asia where the plant is considered an edible weed, and is used as a pot herb, as well as a weak substitute for garlic. Its long tap root has a fragrance and taste some claim is redolent of “horseradish’’. However, I can think of no place in this area where they are so common where one could be sure that the plants have not been contaminated by pesticides or domestic pet wastes. Thus use of it should be avoided in urbanized areas.
But one may ask why is it so common and why does it grow in such abundance?
Garlic Mustard is edible and claimed as a “poor man’s substitute” for garlic. It is claimed to be edible as a pot herb. But encouraging its presence in one’s garden is not advised. Its ability to produce root toxins and form monospecific stands causes it to snuff out the growth of other native plants. So its value as a garlic substitute is somewhat compromised. If it invades a garden it is difficult to eradicate. Today it is classed as a major invasive species.
Garlic Mustard is so well adapted to survival, with its biennial growth pattern, huge seed production, of tiny seeds which are spread widely by ballistic launching. But an even more significant trait is its ability to release inhibitory organic growth chemicals that tend to limit growth of other plants around it. This ability is called allelopathy. Garlic Mustard releases chemicals in the soil which kill off soil fungi which are essential for the health and seed germination and uptake of soil nutrients of many native plants. This property, allelopathy, is reported to be used by some farmers who plant mustard in a field as a winter cover crop and when plowed under in spring the mustard plants leave a residue of soil toxins which help to decrease incidence of early sprouting weed seeds which compete with the farmer’s field crop
I have observed Garlic Mustard patches flourishing in the shade of and surrounded by heavy denser growth of the Giant Japanese Knotweed or Reynoutria japonica. Giant Knotweed is known to use allelopathy —release of soil chemicals— to reduce the growth and germination of plants with which it competes. Knotweed of this species is often found growing in large monospecific patches and is a major invasive speceis as well..more so in fact. Thus few plants are found growing within or close to the Giant Knotweed patches…except Garlic Mustard! I just imagined the war of chemicals going on in the soil around these two allelopathic plants.
Their species reminds us of how much we miss the greenery and also of the resilience and adaptability our floral coinhabitors of this planet of ours. They survive and even thrive in spite of our mismanagemeunt and malfeasance as poor stewards of our planet. Garlic Mustard may even out live us on this planet…think of it!
So given all its abilities to survive—I am impressed with its survivability—and its attractive appearance and this enjoy seeing this lovely member of the Mustard Family thrive in the fall and winter season—then appear among the first greenery in spring. During a winter-thaw the first season low rosette plants often arise from a coating of snow as green as ever, giving a lively touch of color in the dull colors of the cold season. But woe for those who find it in their field or garden patch.
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