Four-leaved Milkweed

(Asclepias quadrifolia)

Status: Endangered (COSEWIC & ESA 2010)

Table of Contents:

Species Identification
Habitat and Biology
Threats/Reasons for Being at Risk
Conservation and Recovery Strategies
How You Can Help

Species Identification:

The Four-leaved Milkweed is a perennial plant that is one of the smallest in the milkweed plant family. This plant grows up to only 80 cm tall, with four light green leaves that grow in opposite pairs. They also grow clusters of small, white-pink flowers at the top of their stems. Seed pods are brown and narrow, and they have tufts of silky white hairs for wind dispersal.

Habitat and Biology:

This species is found in North America, but it is only restricted to the Eastern United States in two distinct regions, with its northern range only extending up into southern Ontario. The far eastern region in the United States ranges from Alabama, Georgia, and South Carolina up to eastern Indiana, Ohio, Pennsylvania, and New York. The slightly more western region can be found from eastern Oklahoma and western Arkansas northward through Missouri, western Illinois and eastern Iowa. In Ontario, there are only two known populations, both of which occur in Prince Edward County. Historical populations occurred in the Niagara River gorge area, as well as up into eastern parts of The Land Between in Lennox and Addington County.

Map taken from Government of Canada: https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/four-leaved-milkweed-2010.html#_Toc266262952

The Four-leaved Milkweed species prefers habitat that was once fairly common throughout North America, but since colonization, agricultural booms, and urbanization, this habitat is now rare. The Four-leaved Milkweed prefers dry, open, rocky, and Oak-Hickory tree dominated deciduous forests. The two populations in Prince Edward County can be found on shallow soils with flat or gently sloping areas near steep limestone escarpments. They are in open and relatively dry forests dominated by Bur Oak, Shagbark Hickory, Ironwood, Easter Red Cedar, Sugar Maple, Basswood, and White Ash trees. These areas also have a fair amount of shrubby understories with Dogwoods, Juniper, and Sumacs.

Milkweed species reproduce only from seeds that are dispersed in the wind or by disturbance. Seeds do not last long in the soil and must germinate quickly in order for this species to survive. Plants are slow to mature, only reaching about 10 cm in the first 3 years of growth. Plants must reach about 33 cm in length in order to be able to produce seeds, which can take anywhere from 7 to 10 years. In order to produce viable seeds, the Four-leaved Milkweed must be pollinated by flying insect species such as bees, wasps, butterflies, and moths.

Threats/ Reasons for being at Risk:

1. Habitat loss: While their specific habitat used to be found throughout North America, colonization has led to significant habitat loss, fragmentation, and degradation. Oak and Hickory forests were historically logged to near extinction for urbanization and agriculture. The relatively flat and dry land provided colonizers with the perfect space for growing crops, and as populations increased so did the need to convert land and grow food, or raise up cities. In fact, 98% of the area in Prince Edward County that houses the two last populations is covered by subdivisions and development.

2. Invasive species: Invasive shrub species like Common Buckthorn are creating dense canopies where sun-loving plants like the Four-leaved Milkweed can no longer survive. They are also being outcompeted by more tolerant invasive herbs like Garlic Mustard and Pale Swallow-wort have been found near Ontario’s only populations, and it is predicted that if these species continue to become well established the Four-leaved Milkweed will soon become Extirpated from all of Ontario.

3. Trampling: Off road vehicles and people and pets travelling off of roads and designated paths pose a threat to the Four-leaved Milkweed since it is a sensitive plant that can be heavily damaged by trampling. This species prefers more open and edge habitats and can be found beside or near trails, which are more likely to be trampled when people venture off of the established trails.

4. Specific habitat needs: There are very few areas left in Ontario that are dry open forests dominated by Oak and Hickory species. In order for this species to survive, other potential areas need to be located and rehabilitated to suit this species needs. More research is needed to determine important habitat characteristics, potential new habitat locations, and important species composition of rehabilitated sites.

Conservation and recovery strategies:

The long-term goal for recovery of this species is to protect the two populations currently in Ontario, and re-establish new populations where possible. The Government of Ontario aims to identify and protect current populations through stewardship and conservation efforts, prioritize important research, implement a long-term monitoring program, confirm known and potential threats, develop Best Management Practices (BMPs), reintroduce populations to their historical ranges, and develop communication and education programs.

How can you help?

Report sightings of the Four-leaved Milkweed plant to The Land Between’s website, iNaturalist, or the Natural Heritage Information Centre, with photos and coordinates.
You and your pets should remain on marked trails at all times to avoid damaging sensitive plants and Species at Risk.
Volunteer with local organizations, nature clubs, or Provincial parks to participate in surveys or stewardship work focused on Species at Risk.
Protect our pollinators! For information on how you can help monitor pollinator populations in Ontario, see http://www.seeds.ca/proj/poll.
Keep areas on your property natural, and encourage the growth and success of natural plants and wildflowers.