Families of Vascular Plants - EEB 337H

The vascular plants of Ontario

There are an estimated 270,000 species of living vascular plants that have been described world-wide; of these, more than 2,000 occur in Ontario (Morton & Venn 1990; Argus 1992; Newmaster et al. 1998).

Map by T. Winterhalt, from The ROM Field Guide to Wildflowers of Ontario, p. 9. © Royal Ontario Museum 2004.

These species are distributed in different combinations that integrate bedrock and climate in such a way as to form the five vegetation zones shown at the left. These range from treeless tundra along the coast of Hudson Bay through the remainder of the Hudson Bay lowland ("Boreal Forest - (1)" on the map) and the boreal forest region ("Boreal Forest - (2)" south to the mixed forest and, in southernmost Ontario, the "Carolinian" or deciduous forest zone.

None of these zones is unique to Ontario, since the first four form bands extending east and west across Canada, while the fifth and smallest is actually part of the vast deciduous forest region of eastern North America.

The aim of this page is to remind visitors to this site of the Ontario context for a study of plant families. Consider the way in which a knowledge of plant classification can inform an appreciation of the provincial flora and the way it sorts out into forest regions across the province. In addition, for students based in Toronto there is an attempt to make the connection between the course content and the the local flora and the "special places" that this flora creates in an urban environment.

Click HERE for a tabular comparison of tree species in the deciduous and mixed forest regions of Ontario.

These species constitute the vascular plant flora of Ontario. They represent approximately 200 families of vascular plants. Few if any of these families are restricted to any of these zones and most, in fact, are found around the globe ("cosmopolitan") or at least throughout the hemisphere ("New World," "circumboreal," etc.). Learning about the flora of Ontario at a level that emphasizes families and their major genera thus also provides the student with a sampling of the plant groups found around the world, not only in the temperate zone but also in both the tropics and the polar regions. The foregoing description applies to the plant species indigenous (i.e. native) to Ontario.

In addition there are numerous exotic species that have been introduced to Ontario from other parts of the world since European settlement began in the 17th century. These species have become naturalized in Ontario, that is they can reproduce themselves successfully without human intervention. Typically, these species share a number of reproductive and other features, such as short (e.g. annual, biennial) life cycles, abundant, easily dispersed, often long-lived seeds and (or) vigorous vegetative reproduction, and the ability to colonize exposed mineral soil. A list of invasive plant species is included in the Ontario chapter of the Society for Ecological Restoration publication, Sustaining Biodiversity - A Strategic Plan for managing Invasive Plants in Ontario (scroll down to the bottom of the page).

Another way in which the word, "flora," is used is to refer to a publication that provides a botanical account of the plants in a particular place. Flora of North America (also online) is an obvious example, as are various Canadian provincial floras (e.g. eFlora BC) and state floras from the United States (e.g. the Oregon flora project). At present, Ontario lacks a treatment of its flora. Instead, botanists rely on checklists, i.e. authoritative lists of names of species making up the flora, but without any further text, such as the one by Morton and Venn (1990), or the Ontario Plant List (Newmaster et al. 1998). In addition, Michigan Flora, by E. G. Voss (1972; 1985; 1996) is extremely valuable, and now is available in its second edition, online (Reznicek et al. 2011).

What factors determine the composition of the Ontario flora?

  • The arbitrariness of political boundaries means that Ontario includes a vast north-south slice of the major east-west vegetation zones shown in the map above. More importantly, the international boundary with the United States lies just south of the northern boundary of the eastern deciduous forest region. The presence of this vegetation zone within Ontario reflects the way in which physical and historical factors (below) operate this far north to create conditions admirably suited for plant growth. These conditions are likewise very favorable for a variety of human activities, with consequences that are also detailed elsewhere.

  • Physical factors are the most obvious explanation for the pattern of Ontario's vegetation.
    • Temperature regimes vary dramatically over the 14 degrees of latitude between the Pelee Islands in the south and the coast of Hudson's Bay in the north. This variation is due to a combination of differences in amount of solar heating and the effect of seasonal airflows on a continental scale. Regionally, the pattern of a shorter, colder growing season in the north and a longer, warmer one in the south is moderated by elevation (the Niagara escarpment and Algonquin dome are cooler than the surrounding lowlands) and the effects of large bodies of water (James Bay, the Great Lakes) that are slow to cool in fall and slow to warm up in the spring. In addition, temperature regimes affect the rate of soil development and the availability of nutrients.
      Natural Resources Canada - Winter Minimum Temperatures Natural Resources Canada - Summer Minimum Temperatures
      Winter Minimum Teperatures

      January Minimum Temperatures (Click on the map to visit the interactive online page).

      Source: The Atlas of Canada, Natural Resources Canada (www.nrcan.gc.ca)

      Accessed 27 September 2009.

      Summer Minimum Temperatures

      July Minimum Temperatures (Click on the map to visit the interactive online page).

      Source: The Atlas of Canada, Natural Resources Canada (www.nrcan.gc.ca)

      Accessed 27 September 2009.

    • Total annual precipitation varies from less than 600 mm in northwestern Ontario to over 1000 mm in the uplands of southern Ontario.
      Natural Resources Canada - Total Annual Precipitation Precipitation key

      Click on the map to visit the interactive online page.


      Source: The Atlas of Canada, Natural Resources Canada (www.nrcan.gc.ca)

      Accessed 27 September 2009.

  • Quaternary history
    • 14,000 years ago all of Ontario was covered by glacial ice. No plant species could survive in Ontario. All the species that grow here today migrated here from places south of the glacial maximum once the glacier began to retreat. Similarly, soil development has been going on only since deglaciation. The process of revegetation can be observed species by species using software and databases that are available on the internet (download the program ShowTime, or visit the NOAA Paleoclimatology website for an interactive online animation of postglacial revegetation, species by species).

These three factors are also integrated in the map shown below:

Barthlott et al. (1998); click to see high resolution version (338K)

"World map of the potential species diversity of vascular plants" by Barthlott et al. (1998). Note the N-S gradient in species density in eastern North America.


Barthlott3.jpg - 24386 Bytes


Additional readings:

Ritchie, J. C. (1987). Postglacial vegetation of Canada. Cambridge University Press, Cambridge.

| What are plant families? | How do we distinguish them? | How and why do we study them? | Selected vascular plant families of Ontario | Reading List | Course outline |

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Please send your comments to tim.dickinson@utoronto.ca; last updated 3-Oct-2011
Coastal tundra Boreal Forest Hudson Bay Lowlands Mixed Forest Mixed Forest Deciduous Forest