Tag Archives: invasive species

Garlic Mustard (Alliaria petiolata) invading Michigan

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Garlic Mustard’s (Alliaria petiolata) native range is Europe. It has invaded North Africa, India, and North America. The first U. S. record is from Long Island in 1868 and it reached Michigan in 1956. Imported for its supposed medicinal values it escaped cultivation and became a serious pest in many woodlands. I saw a large patch of it in 1978 in Rock Cut State Park in northern Illinois. Several acres in size this patch was shading out a colony of Prairie Trillium (Trillium recurvatum). I first saw the plant in Michigan at Warren Dunes State Park in 1981. It was a small patch consisting of a dozen plants. The plant has increased its range and is now found throughout the state.

Alliaria petiolata Garlic Mustard Plants

Garlic Mustard Plants

The plant is easy to identify. It is one to two feet tall (0.3-0.6m), the flowers are white with four petals that narrow at the base, and the leaves are heavily toothed, more or less triangular shape with the veins inset into the upper leaf surface. The seed pods are long and narrow with small ridges, and are similar to native species. They develop quickly, often elongating before the petals drop, and they will continue to develop after the plant is pulled.

Alliaria petiolata Garlic Mustard Flowers

Garlic Mustard Flowers (note developing seedpods in right hand flowers)

It is a biennial, meaning that it flowers in its second growing season. The basal leaves form the first year and are more rounded than the stem leaves on the flowering plant. Garlic Mustard seed germinates at low temperatures (32 degrees F). This gives the seedlings a head start over other native species.

Alliaria petiolata Garlic Mustard Basal Leaves

Garlic Mustard Basal Leaves

Garlic Mustard is allelopathic and destroys the connections between native tree seedlings and mycorrhizal fungi (Stinson K. A, Campbell S. A., Powell J. R. Callaway R. M. 2006). This prevents completion from native tree species and perhaps other plants.

Alliaria petiolata Garlic Mustard Leaves

Garlic Mustard Leaves

For additional reading regarding Garlic Mustard and its control, see the U. S. Forest service fact sheet.

Alliaria petiolata Garlic Mustard Seedpods

Garlic Mustard Seedpods

Copyright 2013 by Donald Drife

Webpage Michigan Nature Guy
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Coltsfoot: a potential invasive species?

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Tussilago farfara flowers

Coltsfoot flowers

Coltsfoot (Tussilago farfara) is a Eurasian species first collected in Michigan in 1840 (See Michigan Flora Online). I saw it for the first time on, March 15th 1978, in Bald Mountain Recreation Area and then along a road in Jackson County about a week later. I wondered if the plant was invading our natural areas, but almost three decades passed before I saw the plant again. I found a small colony in Crawford County in 2006 and that same year I saw 75 plants in Oakland County at Cummingston Park, in Royal Oak, Michigan. The Cummingston Park patch was wiped out when the pond was enlarged.

Tussilago farfara

Coltsfoot flower and seeds

In 2009, the Crawford County station was in flower on May 2nd. Two weeks earlier it was still covered by winter snow. By May 16th the leaves were developing and it was in seed by May 30th. In 2006, the Crawford County station was about 1 meter (3 feet) square. It has since increased to 1 x 2 meter (3×6 feet).

Tussilago farfara leaves

Coltsfoot leaves

The species might be overlooked especially in northern Michigan because it flowers early. It is currently (May 8th) flowering at the Crawford County (near Grayling) site. However, it can be readily identified by the leaves throughout the summer. The leaves have long petioles (leaf stems), are heart-shaped and a distinctive grayish color underneath. Any species that spreads via both rhizomes and seeds should be watched. Coltsfoot has only been collected in eight counties in Michigan but has spread rapidly east of us. Normally it does not compete with native species, preferring to grow where the soil has been disturbed, but it is now moving into native sites in Pennsylvania. This species should be reported whenever it is found (U.S. Forest Service Plant Database).

Coltsfoot initially was imported into this country for its supposed medicinal properties. The leaves were used to treat coughs and bronchial congestion, but possess a liver toxin. There is no current medical use.
Copyright 2013 by Donald Drife

Webpage Michigan Nature Guy
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