The term ‘coastal plain flora’ refers to a small group of plant species that occur in wet areas, mostly lakeshores, in the Georgian Bay area of Ontario.
Most are restricted to a small region which lies roughly east of Georgian Bay, west of Algonquin Park, south of Parry Sound and North of Barrie.
Some representative species are:
Rhexia virginica
Juncus militaris
Xyris difformis
Triadenum virginicum
Panicum spretum
Bartonia paniculata
The most obvious of these species is Rhexia virginica, Virginia meadow-beauty, which has bright pink flowers with yellow centers. Other commonly associated species include:
Lobelia dortmanna
Eriocaulon septangulare
Drosera intermedia
Utricularia cornuta
Rhynchopsora fusca
Viola lanceolata
Habitat requirements
These plants have quite precise habitat requirements. They generally occur on gently-sloping sand or gravel shorelines. There is usually just enough wave energy to remove accumulations of peat that would otherwise form bogs. Water levels fluctuate. High water periods kill shrubs that might otherwise invade the habitat, while low water periods allow the coastal plain plants to regenerate from buried seeds.
Sources of risk
Although these species have occurred in Ontario for some thousands of years, there are two principal threats to their continued occurrence: (1) dams that alter the normal variation of water levels and (2) cottage developments. The principal problem with cottages is that humans prefer the same sort of sandy gently-sloping shorelines, and coastal plain plants cannot tolerate this kind of disturbance. Sometimes, too, cottage associations want water levels regulated and even increased to make it better for recreational boating. These plants are at risk because they have a naturally limited geographical distribution, rather precise habitat requirements, and occur in an area that is experiencing rapid recreational and commercial development. Many of these species are on the rare plant list for Ontario.
Origins
It is thought that these species arrived in the Great Lakes watershed after the last ice age, and when glacial Lake Algonquin still covered much of eastern Georgian Bay. Indeed, one of the most provincially important coastal plain sites at Axe Lake actually appears to be an old shoreline of Lake Algonquin.
Important sites for protection
An extensive survey of lakes in this region was carried out in the 1990s. The most important lakes for these species include Matchedash Lake, Axe Lake, Wahwashkesh Lake, and Wolf Lake. A first logical step for ensuring the survival of the coastal plain flora would be to restrict any further development on any shorelines of these lakes, and to ensure that natural water level fluctuations continue. More details can be found in Keddy and Sharp (1994).
Other disjunct coastal plain communities
There are small areas in Michigan and Wisconsin with similar species. A much larger coastal plain flora occurs in Nova Scotia, with many more nationally rare species – you can read about the Nova Scotia situation here and and consult a field guide here.
More information on the Ontario coastal plain flora
General botany and discoveries
Reznicek, A.A. and R.E. Whiting. 1976. Bartonia (Gentianaceae) in Ontario. Canadian Field-Naturalist 90: 67-69.
Reznicek, A.A. 1994. The disjunct coastal plain flora in the Great Lakes region. Biological Conservation 68: 203-215.
Description of one site on the old shore of Lake Algonquin
Keddy, P.A. 1981. Vegetation with Atlantic coastal plain affinities in Axe Lake, near Georgian Bay, Ontario. Canadian Field-Naturalist 95: 241-248.(Download PDF)
Importance of water-level fluctuations and buried seeds
Keddy, P.A. and A. A. Reznicek. 1982. The role of seed banks in the persistence of Ontario’s coastal plain flora. American Journal of Botany 69: 13-22. (Download PDF)
A survey and ranking of priority sites for conservation
Keddy, C.J. and M.J. Sharp. 1994. A protocol to identify and prioritize significant coastal plain plant assemblages for conservation. Biological Conservation 68: 269-274. (Download PDF)
Many of these species are on the rare plant list for Ontario.
To download the rare plant list from the Natural Heritage Information Center (NHIC) go here.
(Note: This page uses the species names used in the published papers from the 1990’s. Some names have changed over time and will have to be adjusted in future work.)
Paul Keddy, Ph.D. 