Prepared by G. Poisson, K. Ursic and M. Ursic

Four-leaved Milkweed (Asclepias quadrifolia) is a perennial herb of woodlands and forest edges that grows up to 80 centimetres in height. Leaf arrangement is in opposite pairs, with each pair separated by a short internode, giving the appearance of being whorled. In southern Ontario, maturity is attained between 5 to 10 years and reproduction is sexual. The species flowers from late May till the end of June. Pollination is mostly by bees (Bombus spp.) and butterflies (Lepidoptera). Tufted seeds develop in a pod that matures over the summer. Seed dispersal is by wind. Populations consist of scattered individuals or groups.

In Ontario, populations of Four-leaved Milkweed have been recorded from only two localities: the Bay of Quinte region along the north shore of Lake Ontario and the Niagara River Gorge connecting Lake Erie and Lake Ontario. Populations at these localities, as well as those found in New York, Vermont and New Hampshire, are at the northern limit of the species range in North America. At present, it is believed that there are only two extant populations remaining in Ontario. Both of these populations are situated in Prince Edward County in the Bay of Quinte region. Historically, Four-leaved Milkweed populations have also been recorded from the neighbouring Lennox and Addington County of the Bay of Quinte region as well as from the Niagara River Gorge.

Four-leaved Milkweed occurs in a provincially rare habitat type (Bur Oak – Shagbark Hickory Woodland on shallow soil over limestone) and there are fewer than 200 known mature individuals. This species was assessed as endangered by the Committee on the Status of Species at Risk in Ontario (COSSARO) and designated under the Endangered Species Act, 2007. At the federal level, this species was assessed as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

Major threats to conservation of the remaining populations of Four-leaved Milkweed in Ontario include:

  • habitat loss due to residential and agriculture land uses;
  • habitat loss and degradation due to woody species succession and invasive species; and
  • impacts from anthropogenic activities such as hiking and all terrain vehicle use.

The long-term recovery goal for Four-leaved Milkweed is to protect extant populations and re-establish new populations in appropriate habitat where feasible.

Specific objectives are listed below in priority sequence as follows.

  1. Identify and protect extant populations and associated habitat through public ownership or conservation easement.
  2. Prioritize and implement necessary research activities to gather required information for effective species recovery.
  3. Implement a standardized long-term monitoring program to assess the status of extant populations.
  4. Confirm known and potential threats to extant populations.
  5. Develop and implement site specific best management practices to address known and potential threats
  6. Investigate the feasibility of reintroduction at current and historic sites and other suitable habitat.
  7. Develop a communication and outreach strategy.

The approaches to recovery emphasize the protection of existing populations and their habitat, monitoring existing populations to identify and mitigate threats through management, conservation of the genetic pool through gene banking, and plant propagation and re-introduction at extant sites and/or suitable new sites, where deemed feasible.

It is recommended that the minimum area that should be considered in developing a habitat regulation for Four-leaved Milkweed include the area occupied by all extant populations and the surrounding extent of the vegetation community type (based on Ecological Land Classification for southern Ontario) in which it occurs. This will allow for future growth, expansion and migration of these populations. The habitat regulation should be subject to revision as more information on the species' ecology, habitat requirements and its pollinators' habitat requirements becomes available.