Prepared by Judith Jones

Willowleaf Aster (Symphyotrichum praealtum) is listed as threatened under Ontario’s Endangered Species Act, 2007 and on Schedule 1 of the federal Species at Risk Act (SARA). It is a herbaceous, perennial plant that spreads vegetatively from rhizomes, forming colonies. The species is fall-flowering with pale lavender flowers. Willowleaf Aster requires cross-pollination from a genetically different individual for seed set. A recent genetic study found considerable genetic variability both among and within Willowleaf Aster populations in Windsor.

In Canada, Willowleaf Aster occurs only in southwestern Ontario. At least nine natural and two restoration populations are known to be extant. Most individuals of Willowleaf Aster are found in the City of Windsor and Town of LaSalle within an area of approximately 20 km2. In this strategy, this area is treated as a single population. Outside this area, there are five other populations in Windsor – LaSalle, two elsewhere in Essex County, and one on the Walpole Island First Nation. In addition, there are four populations with unknown status and four considered historical or extirpated. Tens of thousands of stems of Willowleaf Aster were found during preparations for the Detroit River International Crossing and Windsor Essex (Rt. Hon. Herb Gray) Parkway and are being transplanted into 34 restoration sites in Windsor.

In Canada, Willowleaf Aster is found in tallgrass prairies, oak savannas, meadows and woodland openings as well as open anthropogenic habitats such as abandoned fields, along railways and roadsides, and on the banks of streams, drains and ditches. The habitat must have disturbance, such as fire or human-made clearing, to remain open and suitable. The species prefers moist soils.

Threats to Willowleaf Aster include development, an altered disturbance regime, invasive species, conversion of habitat to agricultural use, mowing, herbicide use, habitat degradation and deer browsing.

The recovery goal is to maintain the current distribution, number and viability of all extant populations and corresponding subpopulations of Willowleaf Aster by maintaining, improving, and protecting habitat and reducing other threats. The protection and recovery objectives are to:

  • assess threats and plan measures for mitigation and reduction;
  • maintain or improve habitat suitability at all existing sites;
  • ensure adequate habitat and species protection by monitoring and initiating recovery actions when necessary; and
  • fill knowledge gaps.

It is recommended that the area to be prescribed for a habitat regulation include all sites where Willowleaf Aster has been reported unless the species is proven extirpated. In natural tallgrass prairie and oak savanna vegetation, it is recommended that the entire Ecological Land Classification (ELC) polygon in which Willowleaf Aster is present plus a protective zone of 50m around the outside of the polygon boundary be prescribed. In anthropogenic habitat and in natural tallgrass woodland vegetation it is recommended the entire continuous open area be prescribed, as well as a 50 m protective zone beyond the outside boundary, with a minimum 50 m radial distance around patches of Willowleaf Aster. In linear habitats, such as railway embankments, it is recommended that the prescribed area have a maximum length of 100 m. It is recommended that restoration sites be included in the habitat regulation.