The Palisades Interstate Park is a National Historic Landmark.
Palisades Interstate Park in New Jersey

Another “Side” of Invasive Species

Trapa natans. From An illustrated flora of the northern United States, Canada and the British Possessions, 1913.
Alliaria petiolata. Drawing: USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 2: 170.

“Another ‘Side’ of Invasive Species” was first published in the March-April 2008 issue of “Cliff Notes.”



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Plants and animals that are not native to an area, but then not only survive there but run out of control, are referred to by scientists as “invasive” species. People often say, “Invasive species are bad,” but when asked exactly why, many are stumped. What is “wrong” with these species?

Aside from crowding out native species, “invasives” can disrupt the natural processes of whole ecosystems. Since they are out of their natural habitat, there is often little or nothing to keep these uninvited visitors in check. One of these guilty offenders is garlic mustard (Alliaria petiolata), a three-foot tall biennial weed with small white flowers and rigid heart-shaped leaves that smell like garlic when crushed. Originally brought here from Europe in the late 1800s, the plant is now common throughout most of North America (including in this park!), growing not only in disturbed areas, where invasive plant species typically proliferate, but also underneath the canopy in undisturbed forests.

And herein lies the big problem.

Just beneath our forest floors lives a complicated network of mycorrhizal fungi, a widespread type of ground fungus native to North America. Mycorrhizal fungi have a symbiotic relationship with woody plants, tree saplings in particular. The fungi help the young plants take up nutrients in exchange for carbon. In an ideal system everybody wins, but recent studies have shown that the non-native garlic mustard is severely disruptive to this plant–fungal association. A. petiolata, like all members of the mustard family, is not dependent on the fungus for survival and in fact actively kills the surrounding fungal system. While native mustards have adapted to coincide with mycorrhizal fungi, the invasive European variety has not and is starting to negatively affect forest ecosystems.

Being relatively delicate, tree saplings here depend on mycorrhizal fungi for growth and survival. If garlic mustard enters a mature forest area, the fungus is severely affected — as is its symbiotic relationship with the saplings of dominant tree species. Studies have shown that tree saplings in areas where there is garlic mustard grow more slowly, and therefore have a lesser chance of survival. Essentially, the newer generations of trees are being stunted, a situation which could prove devastating for the future of our forests. It may seem insignificant if one year a small patch of garlic mustard invades a forest and hinders sapling survival, but that small patch may pose a major problem in a few decades.

So what can be done to control this persistent invader? In undisturbed native ecosystems, one thing tends to balance out another. Invasive species, though, find little or nothing to check their numbers. There is in fact no native species of insect or animal that feeds on garlic mustard. Or is there…?

Unknown to many, garlic mustard is not only edible, but can be delicious! The leaves are only slightly bitter (becoming more so with age) and taste like, yes, garlic, while the taproot has a pungent horseradish-like quality. The leaves can be added to salads with milder greens, sautéed in a sauce, or steamed. The plant can be found and eaten year-round: in winter the basal rosettes stay green and low to the ground; in spring and summer the plant reaches its full height and produces the most leaves; in fall the seeds can be gathered and eaten as well. Do you have a patch of garlic mustard in your backyard? Try these tasty recipes — and perhaps help to save our forests…!


Garlic Mustard Pesto

4 cloves garlic
3 Tbs. garlic mustard taproot (ground)
¾ cup parsley
1 cup garlic mustard leaves
1 cup basil leaves
1 ½ cups olives, pitted
2 cups walnuts or pine nuts
½ cup yellow miso
1 ¼ cups olive oil

Blend all ingredients together to make a paste, leaving nuts coarsely chopped. Use on your favorite pasta or spread on toast. Makes 4 cups.

Garlic Mustard Lemon Sauce

2 cups water
5 Tbs. flour
3 Tbs. sugar, honey, or other sweetener
¼ cup lemon juice
¾ tsp. salt
¾ tsp. ground cloves
¾ tsp. allspice
5 tbs. olive, peanut, or vegetable oil
6 cups garlic mustard leaves
3 cloves garlic

Stir all ingredients, except garlic mustard leaves, garlic, and oil, in a saucepan and bring to a boil. Stir fry garlic mustard and garlic in oil for 2 minutes. Pour sauce over garlic mustard mix and cook on high for 3 minutes. Makes 6 servings.