Let’s talk about Michigan’s invasive herbs: How to identify them and the threat they pose

Officials warn residents about 8 invasive herbs

The eight invasive herbs in Michigan. Images and credits can be found here: https://www.michigan.gov/invasives/id-report/plants/herbs (State of Michigan)

There are eight invasive herbs that Michigan officials want residents to be aware of.

You’ve probably heard about giant hogweed as it poses a public health hazard that ranks higher than poison ivy, poison oak and poison sumac in its potential to harm humans. The sap from the giant hogweed can cause a severe skin reaction known as photo-dermatitis.

But that’s not the only invasive herb of concern. Below I’ll go over the eight Michigan has listed online, how to identify them and what threat they pose to you or the ecosystem.



Butterbur

Butterbur has been detected in Michigan. It is also called Butterfly Dock or Pestilence Wort. Its scientific name is petasites hybridus.

How to identify it:

  • Perennial, herbaceous flowering plant grows to 6 feet.
  • Simple, round to heart-shaped leaves are 1-2 feet across, with dense hairs on the underside.
  • Single leaves grown on hollow, ridged, 3-4 foot stems somewhat similar in appearance to rhubarb.
  • Flowers are pink to purple and grow on a spike that emerges before foliage in spring.
  • Fruit and seeds appear in a white, flower-like tuft.

Where it is found: It is found in shaded areas with moist soil, including river banks, shorelines, wetland edges, forested floodplains and roadside ditches. It has been found between New York and Ohio.

Why is it a local concern?: It spreads easily and its large leaves shade out other vegetation, leaving bare earth beneath.

Click here to learn more about butterbur.

Garlic Mustard

Garlic mustard is established in Michigan. Its scientific name is Alliaria petiolata.

How to identify it:

  • An herbaceous, flowering plant that smells like garlic when crushed.
  • Heart-shaped basal rosettes (leaves) appear in year one at ground level.
  • In the second year, stems shoot up (1-4 feet) and develop flowers and seeds.
  • Leaves become more toothed and triangular in shape.
  • Clusters of tiny, white, 4-petaled flowers bloom in early spring.
  • Seed pods are green, long and narrow and look like stems – turning brown in fall.

Where is it found? It thrives in wooded areas and can tolerate deep shade.

Why is it a concern? It spreads quickly through woodlots and outcompetes understory plants, including tree seedlings. Seeds can be transported or blown around by vehicles. It has compounds that can limit seed germination in other species.

Click here to learn more about garlic mustard.

Giant Hogweed

Giant hogweed is established in Michigan. Its scientific name is Heracleum mantegazzianum

How to identify it:

  • White flowers in an umbrella-shaped cluster up to 2.5 feet across.
  • Plant is 7 to 14 feet tall.
  • Stems are green with purple splotches and visible, coarse, white hairs.
  • Leaves are up to 5 feet wide, lobed and deeply incised.

Where is it found? It prefers open, slightly moist areas but can be found in a variety of habitats.

Can it harm humans? Yes. Its sap can cause a severe skin reaction known as photo-dermatitis or photo-sensitivity and damage to the eyes. If you have come in contact with hogweed sap you should wash the exposed area immediately, keep that area out of sunlight and seek medical care.

Click here to learn more about giant hogweed and see the plants it’s commonly mistaken for.

Read: Worse than poison ivy: How to identify, report dangerous hogweed plant found in Michigan

Himalayan Balsam

Himalayan Balsam has been detected in Michigan. Its scientific name is impatiens glandulifera. It’s also known as ornamental jewelweed, touch-me-not, Indian jewelweed, policeman’s helmet.

Officials are concerned because this herb can alter the behavior and composition of pollinating insects.

How to identify it:

  • Grows between 3 and 6 feet tall.
  • Purple/red stems are smooth and hollow.
  • 5-10 flowers on each stems.
  • 5 petals per flower-purple, pink or white in color.
  • Fruit capsules explode when ripe and touched.

Where is it found? It can be found in wetlands, forests, gardens, yards and on the side of the road.

What is concerning about it? It competes with native species and alters the behavior and composition of pollinating insects. It can also alter water flow at high densities which can increase risk of erosion and flooding.

Click here to learn more about Himalayan balsam and see the plants it’s commonly mistaken for.

Japanese Chaff Flower

Japanese chaff flower has not been detected in Michigan, but is on the watch list. Its scientific name is Achyranthes japonica.

How to identify it:

  • Perennial herbaceous plant growing 3-6 feet high.
  • Simple, smooth-edged leaves with pointed tips grow opposite.
  • Flower is a green, bottle brush-like spike with no petals.
  • Stem at the ground is red, even in seedlings.
  • Stems remain erect and turn brown to orange-brown in the fall and winter.

Where is it found? It is native to East Asia. It prefers partial sun and moist areas, including floodplains and shorelines. It can also grow in shade, full sun and dry areas. It has been found along the Big Sandy and Ohio rivers: Illinois, Indiana, Ohio, Missouri, Kentucky, West Virginia, Tennessee, Alabama and Georgia.

What is concerning about it? It outcompetes native species and forms large, dense strands in floodplains, forested wetlands, ditches and vacant land and other disturbed edge habitats.

Click here to learn more about Japanese chaff flower and see the plants it’s commonly mistaken for.

Purple Loosestrife

Purple loosestrife is established in Michigan. Its scientific name is lythrum salicaria.

How to identify it:

  • Perennial herb with a woody, square stem covered in downy hair.
  • Height varies from 4 to 10 feet.
  • Leaves are arranged in pairs or whorls.
  • Magenta flower spikes with 5-7 petals per flower are present for most of the summer.

Where is it found? It thrives along roadsides and in wetlands. Seeds can germinate in water. It prefers full sun, but can tolerate shade. It has been found in every state except Florida.

What is concerning about it? It can replace native vegetation. It can lead to a reduction in plant diversity, which reduces habitat value to wildlife.

Click here to learn more about purple loosestrife.

Spotted Knapweed

Spotted knapweed is established in Michigan. Its scientific name is centaurea stoebe.

How to identify it:

  • An herbaceous, bushy, perennial plant growing 2-3 feet.
  • Elongated, bluish- or grayish-green leaves divided into lance-shaped lobes.
  • Pinkish-purple flowers are thistle-like and bloom from July through September.
  • Long, stout tap-root can send shoots to start new plants.
  • Seeds are carried on fine, white tufts emerging from the flower base.

Where is it found? It is found in open fields or scrub-shrub areas with poor soils or sands and also in disturbed areas, hay fields and pastures.

Can it harm humans? It can be a skin irritant. It is poisonous to other plants and threatens pastures and dry ecosystems.

Click here to learn more about spotted knapweed.

Wild Parsnip

Wild parsnip has been detected in Michigan. Its scientific name is pastinaca sativa.

How to identify it:

  • Biennial flowering herb on a single stem that grows to 5 feet tall.
  • Leaves consist of 2 to 5 pairs of leaflets that grow across from each other along the stem, and one diamond-shaped leaflet on the end.
  • Leaflets are toothed and often shaped like a mitten.
  • Yellowish green flowers form umbrella-shaped clusters 4 to 8 inches across.
  • Flowers bloom in June and July.
  • Stem is green, 1-2 inches thick and smooth with few hairs.

Where is it found? It is often found in open areas, pastures, fields, roadsides and disturbed areas. It is found everywhere in the U.S. except for Florida, Georgia, Alabama, Mississippi and Hawaii.

Can it harm humans? Stems, leaves and flowers contain chemicals that can increase skin sensitivity to sunlight and cause severe rash or blistering.

Do other plants look similar? Yes. Other members of the carrot family, including cow parsnip, angelica and Queen Anne’s lace, are often misidentified as wild parsnip.

Click here to learn more and review similar plants.


Is there something in Michigan that you think we should write about? Reach out to me via email at kclarke@wdiv.com. See previous coverage by clicking here.



About the Author:

Kayla is a Web Producer for ClickOnDetroit. Before she joined the team in 2018 she worked at WILX in Lansing as a digital producer.