Prepared by Judith Jones, Jarmo Jalava and John Ambrose

The Large Whorled Pogonia (Isotria verticillata) is an orchid with a single yellowish-green flower above a whorl of leaves. The species requires mycorrhizal fungi in its roots for nourishment. The Large Whorled Pogonia can remain dormant, sometimes being absent for a number of years. The species is listed as endangered under the provincial Endangered Species Act, 2007and the federal Species at Risk Act.

Canadian locations of Large Whorled Pogonia are all in Carolinian woodland in southwestern Ontario. There are two populations presumed extant, one population possibly extant and one historical population last seen in 1879. The three populations declined steadily from the 1960s to the early 1990s. The last observation of the species in Canada was in 1996 despite some subsequent searches. However the maximum dormancy period for this species is unknown and sites have not been searched in consecutive years; therefore it is premature to presume the species is extirpated.

The habitat of Large Whorled Pogonia generally is moist, deciduous or mixed forest with a semi-open canopy on sandy acidic soil with thick leaf litter and abundant humus.

Human impacts on habitat (land clearing, incompatible forestry practices and trampling) have probably played a significant role in the decline of Large Whorled Pogonia in Canada. Other threats include the effects of fragmentation of woodlands and resulting isolation of small populations and natural processes such as flooding by beaver. As well, exotic earthworms and atmospheric pollutants are potential threats that may alter soil conditions and deleteriously affect the symbiotic mycorrhizal fungi that the orchid requires to survive. Invasive plant species may also be a potential threat.

Determining if any Canadian populations are extant is an urgent knowledge gap. The recovery goal is to recover and maintain long-term, self-sustaining, viable populations of Large Whorled Pogonia and its habitats within the current and historic range in southern Ontario. Recovery for Large Whorled Pogonia will present a number of challenges. Propagation and re-introduction can be difficult to do with orchids because of the necessary mycorrhizal associations. The objectives toward achieving the recovery goal include the following.

  • Determine current status of Large Whorled Pogonia populations in Ontario through inventory of the three known populations, historic reports and other potential habitat.
  • Protect and manage habitat to maintain extant populations in Ontario through:
    1. appropriate management of public lands;
    2. appropriate land-use planning for private lands;
    3. stewardship on private lands;
    4. site securement; and
    5. site restoration and rehabilitation.
  • Address knowledge gaps relating to the biology, ecology, habitat and threats of Large Whorled Pogonia in Ontario.
  • Coordinate recovery activities with other plant species of the draft Carolinian Woodland Plants Recovery Strategy and work towards increasing the amount of high-quality interior moist forest habitat (to enhance the chances of natural dispersal and colonization of new sites).
  • Develop educational and outreach materials for naturalists, orchid enthusiasts and the general public highlighting the significance, uniqueness and vulnerability of the species.
  • Investigate the feasibility of reintroducing Large Whorled Pogonia to sites where it is deemed extirpated if suitable habitat remains, or to other suitable habitat.

The maximum length of dormancy for this species is not known, so as a precautionary principle a habitat prescription should be made for the populations presumed or possibly extant until their status can be clarified.

It is suggested that the area to be prescribed as habitat should be the Ecological Land Classification (ELC) vegetation type around the three documented populations plus any contiguous area of deciduous or mixed forest cover that has >10 cm of duff and humus and soil pH of 4.0 to 5.5. If the plants reappear in any given year and it becomes possible to fill knowledge gaps, these parameters can be further refined.