Southern Ontario Vascular Plant Species List - Conservation Ontario

Total Number of Species
John Morton and Joan Venn, University of Waterloo, published A Checklist of the Flora
of Ontario - Vascular Plants in 1990. The total number of species in the province at that
time was 2,888 species (including subspecies and varieties). In 1998, the Ontario Plant
List was published by the Ontario Forest Research Institute, a branch of the Ontario
Ministry of Natural Resources, which provided a listing of 3,340 vascular plants (tree,
shrub, herbaceous and fern species). A more current number of over 3,400 plant species
is listed on the Natural Heritage Information Centre (NHIC) website.
Our provincial flora is dynamic in nature, changing from year to year. Each year seeds
from non-native species are introduced into new environments within the jurisdictional
boundary of Ontario. Sometimes these are accidental introductions, where seeds are
attached to incoming railway cars, boats, or automobiles. Other introductions are a
consequence of planting horticultural species in urban landscapes, and the subsequent
dispersal of seeds into surrounding areas.
There are also a few instances when plants were deliberately introduced into our flora.
For example, White Mulberry (Morus alba) was planted in eastern north America to
provide a food source for the Mulberry Silkworm (Bombyx mori). It was hopped that a
North American silk industry could be developed replacing the importation of silk from
China and Japan. However, the invention of modern day synthetic materials put an end to
this endeavour in the mid 1940’s. Today this introduced tree species from northern China
is found in Ontario, Quebec and most of the United States.
Another reason for updating this species list is the discovery of previously unknown
native plants species after the release of the OPL in 1998. This includes the addition of
Swamp Cottonwood [Populus heterophylla], discovered in Essex County; Dwarf
Dandelion [Krigia virginica] in Pinery Provincial Park, and Trailing Bush Clover
[Lespedeza procumbens] discovered in Haldimand County. There are still some regions
of the province that are poorly botanized and may still yield some new discoveries to our
botanical flora.
Some native species are disappearing from our flora as a result of the introduction of
fungal pathogens which have been detrimental to some of our native trees. Two species in
particular, American Chestnut (Castanea dentata) and Butternut (Juglans cinerea) are
disappearing due to the introduction of infectious microorganisms. Chestnut blight and
Butternut canker, along with a loss of suitable habitat have the potential to eliminate these
species from our flora. Other plants such as Ginseng (Panax quinquefolius) are
disappearing as a consequence of the over harvesting of its underground tubers.
As a result of these influences, the total number of species in Ontario will always be
fluctuating to some extent. At best all we can do is provide a listing of the observed
documented plant species, and continue to protect the varied habitats that are essential for
their survival.
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