An Introduction to Rare Plants of Ontario

This website is intended to educate the public about rare plants in Ontario. We have selected 12 plants to showcase in our database and have provided a complete list of rare plants in Canada. For complete scientific information on all plants, select one of the sites from our links page.

Introduction Ontario's Flora - Background Information Vegetation Zones Ontario's Plant Geography - Climate, Glaciation and Vegetation Bedrock geology Soil texture and composition Available water Distribution of Rare Species

Introduction Plants - what would our world be without them? All we have depends on these green marvels, for only they are able to capture and store the sun's life-giving energy in a form that other living things can use. Yet despite its importance, our green legacy is fast disappearing, and with it a large variety of dependent animal life.	A moose feeding at Algonquin Park
Forest industry in the Brazilian Rainforest	According to the World Wildlife Fund, we will lose an average of two plant species each day for the next 50 years. Around the world up to 40,000 species are in trouble, facing pressures that may drive them to the brink of extinction. Though public attention has recently focused on the fate of tropical rainforests, plants found much closer to home face similar pressures, and this site has been created to draw attention to that fact. Loss of biodiversity as a result of habitat destruction is a global problem, be it deforestation for cattle ranching in Brazil, or draining a small southern Ontario wetland for a new housing development.
The species discussed in this site vary in past and present distribution and abundance. Some are among our rarest plants, while others are still common in localized areas. Certain species shown in the on-line database ere never abundant and so have always been relatively vulnerable. Others were once more common, but have not been able to withstand widespread habitat loss. We have tried to represent a cross-section, rather than select the 12 most threatened species. Though this site focuses on wildflowers, it is important to realize that many of our rarest plants are far less conspicuous, including certain grasses, sedges and ferns. We hope that you will find this material to be of assistance as you integrate information on Ontario's endangered species into your teaching. Please help us to improve future editions of this site, by sending your comments and suggestions to our e-mail address.

^top

ONTARIO'S FLORA - BACKGROUND INFORMATION

FACTORS INFLUENCING PLANT DISTRIBUTION

Vegetation Zones in Ontario (go to clickable search map) Different parts of the world are well known to have different vegetation. The plants of the arctic are obviously different from those of the tropics, and those of the desert are unlike those of the rain forest. Even within temperate regions, there are vegetation zones with distinctly contrasting aspects. Ontario, which exceeds 15 degrees in latitude from south to north and approaches 21 degrees in longitude from east to west, includes portions of four such zones (or five in some classifications). These four zones divide the province from south to north, and are correlated with climatic factors, primarily temperatures. The terms given to these divisions differ from one reference to another. They have been called life zones, life areas, plant formations, forest regions and floristic provinces. The prevalent term for such a zone in modern scientific literature is biome, which recognizes that these zones differ from one another not only in the dominant vegetation of undisturbed habitats, but also with respect to all groups of plants, animals and microorganisms.
A hardwood forest in Eastern Ontario	The names given to the individual vegetation zones or biomes also vary from one reference to another. In Ontario, however, the southernmost zone in the province is usually referred to as "Carolinian Life Zone" or "Carolinian Forest". This life zone barely extends into Canada; most of it lies in the United States, where it is often called the Eastern Deciduous Forest. The prevailing natural vegetation of this zone, as one of its names implies, is deciduous forest, with more tree species per unit of area than in any other zone in Canada. North of this zone is the Hemlock-White Pine-Northern Hardwoods zone or Great Lakes-St. Lawrence Forest (essentially comparable to the Alleghenian Life Zone), with mixed forests of deciduous and coniferous trees. Some of the dominant tree species of the Carolinian or Deciduous forest are also among the dominants in this zone. Many of the Carolinian species are absent however, and some tree species that are infrequent in the Carolinian forest are among the dominants in this zone.
The next zone northward is the Boreal Forest or Northern Coniferous Forest, also known as taiga. The southern part of this zone, where the forest is dense and the trees are relatively large, constitutes the Closed Boreal Forest (Canadian Life Zone). The northern part, toward James Bay, is generally recognized at least as a distinct subdivision or sometimes as a distinct zone, called the Open Boreal Forest or Forest and Barren region (Hudsonian Life Zone). Here the trees are smaller and scattered, with shrubs, sedges, mosses, and lichens covering much of the area. Only a proportionately small part of Ontario, near the shore of Hudson Bay and the northern part of James Bay, is the Arctic Tundra (Arctic Life Zone). This zone is devoid of trees; the vegetation is dominated by small shrubs, sedges, mosses, and lichens. The boundaries of these vegetation zones or biomes are by no means distinct in nature. Well within the Carolinian zone as mapped, the vegetation of north- and northeast-facing slopes is more characteristic of the Hemlock- White Pine-Northern Hardwoods zone, and Boreal Forest species prevail around some wetlands. The presence of some Tall-grass Prairie communities within generally forested regions is discussed below.	Dense boreal forest

^top

Ontario's Plant Geography - Climate, Glaciation and Vegetation Glacial ice covered our entire province as recently as 15,000 years ago, and so our flora is a relatively new phenomenon. As the most recent continental glacier melted and the Ontario's climate underwent a series of changes, plant species gradually migrated northward. In some cases, isolated populations of species characteristic of more northern or western regions represent remnants of earlier stages in Ontario's vegetation. When the receding glacial front was still in southern Ontario, ca. 9000 years ago, at least a narrow zone of arctic species is believed to have to have existed adjacent to it, with predominantly coniferous forests much like the present-day Boreal Forest covering an extensive zone where deciduous forests prevail today.	Glacier in the Yukon Territory
An active glacier in retreat, carving out the landscape	As the climate continued to become warmer and the glacier continued to recede, the arctic and boreal species spread northward and were generally succeeded in present-day southern Ontario by the species of the Hemlock-White Pine-Northern Hardwoods and Deciduous forests. Some arctic and boreal species persisted, however, in exceptional habitats where local environmental conditions resembled those prevalent farther north.
Likewise, some populations of prairie species are presumably remnants of an expansion of prairies to the north and east of their present distribution that occurred during a relatively warm, dry period ca. 3500 years ago. Other prairie species in contrast, obviously arrived at some Ontario sites much more recently, through long-distance dispersal. Their later arrival is indicated by their presence in newly disturbed sites that have provided prairie-like conditions only since the forest was cleared. Still other species, although regularly found in prairies, are also characteristic components of the vegetation of open or naturally disturbed areas within the forested zones.

^top

Although climate determines the boundaries of the major vegetation zones, there are many other factors that determine the distribution of plant species, some operating on a scale nearly as large as that of climate, others being much more local in their effects: 

Bedrock geology is a major factor, because the underlying rocks are generally the parent material of the mineral component of the soil. Most of Ontario south of the French and Mattawa rivers is underlain by sedimentary rocks, and most of these rocks are high in calcium and magnesium, producing fertile soils.	The Scarborough Bluffs, near Toronto, ON
In contrast, an area bounded approximately by the routes of the Trent-Severn and Rideau waterways and by the St. Lawrence and Ottawa valleys is geologically an outlying portion of the Canadian Shield. The rocks here are igneous and mostly low in calcium and magnesium. They are slower to weather; consequently there is much exposed bedrock, and the derived soil is coarse-textured, acid, and relatively low in most mineral nutrients. Northern Ontario is largely underlain by the Shield, and the same generalities apply to most of its mineral soils. ^top
Soil texture and composition often vary significantly even within a small area and greatly affect the distribution of plant species. Some parts of southern Ontario for example, were formerly the beds of lakes formed by glacial meltwater; the soils derived from such lake-bed deposits are generally fine-textured and rock-free. Rushing rivers in front of or under the melting glacial ice deposited large quantities of sand and gravel that still affect modern soil texture.	An example of lake formation by glaciers
Moraines -- ridges of mixed coarse and fine rock fragments deposited by the glaciers -- are the sites of rocky soils with diverse components. Great depths of highly organic soils have accumulated in some wetlands. All of these soil types, and others, occur within a single climatic zone, and each soil type supports plant species not found elsewhere, as well as species -- like poison ivy! -- that grow well in many types of soil. ^top

Available water obviously determines the distribution of plant species. Some, like the Yellow Lotus and the more familiar water-lilies, are aquatic, and grow only where there is permanent standing water. Water clarity, depth, and current all affect the distribution of aquatic plants. Some plants, although not found in open water, are associated with the relatively wet habitats of marshes, swamps, fens, and bogs, some being tolerant of seasonal flooding whereas others survive only above the high-water line. Species requiring well-drained sites differ in their ability to withstand drought. Consequently topography, as it determines the availability of various kinds of wet and dry habitats, also determines the distribution of plant species.

A Great Blue Heron at home in a marsh

Many other factors affect the geographic ranges and abundance of species. Some factors, like the environmental tolerances of pollinators or parasites, are less readily discerned, and so much remains to be learned about why some Ontario plants are rare. Any attempt to preserve a plant population or an entire species from extinction requires a great deal of research. Merely moving individual plants away from a construction site is not enough! ^top

DISTRIBUTION OF RARE SPECIES Many of Ontario's rarest species, including nearly all of the province's rare trees, are restricted to the Carolinian zone. One reason for the rarity of these species is that this zone is by far the smallest in Ontario. Also, since this part of Ontario is the most attractive for human settlement and the most productive agriculturally, much of its natural vegetation has been destroyed by urban and agricultural development. The remaining natural vegetation in this zone is now fragmented into small tracts that are stressed from all sides. Even though an area may now be designated a nature reserve, its vegetation is subjected to pressures from the surrounding cities, through air and water pollution, siltation, excessive or abusive recreational use, naturalization of introduced weeds and commercial exploitation of native plants.	Construction's effect on natural lands
Agricultural lands	Some rare species, although restricted to the Carolinian zone, are not part of the characteristic flora of the Carolinian forest. These include prairie species. The Tall-grass Prairie is yet another vegetation zone, associated with drier climates than those of the forested regions to the east. Its northern boundary extends from its eastern limits in Ohio northwest to southern Manitoba. Just a few small outlying areas of prairie, near Lake St. Clair and the western part of Lake Erie, were part of Ontario's natural vegetation at the beginning of European settlement. Much of this vegetation has been eliminated by the advance of agriculture and urbanization. Relatively few of Ontario's rare species are found in the extensive Hemlock-White Pine-Northern Hardwoods or Closed or Open Boreal Forest zones. The exceptions are mostly either primarily Appalachian species in the easternmost part of the province, or western species that reach their eastern limits near the Manitoba border. The tundra has a number of species classified as rare in Ontario, these being arctic species with ranges barely extending into Ontario along the Hudson Bay shore.
Other rare species are not part of the prevailing vegetation of any of the major vegetation zones, but instead are restricted to special habitats of limited extent within one or more of these zones. Species growing in crevices in cliff faces are an example. Some of the species associated with the Niagara Escarpment have highly restricted ranges in southern Ontario, because few steep outcrops of calcareous rocks occur anywhere else at comparable latitudes. Some particularly attractive rare species grow in fens. These relatively small wetlands are somewhat like bogs in aspect but, unlike bogs, are rich in calcium and magnesium from the surrounding calcareous mineral soil and bedrock. Both cliff and fen habitats have been considerably reduced in extent, the former by quarrying, the latter by drainage for agricultural purposes. In modern times, these habitats face more subtle threats, such as recreational use of the Escarpment and development that affects the level and the quality of water in fens.
Rocky shores of Lake Superior	Some special habitats supporting rare and especially attractive plants are found along the sandy shores of the Great Lakes, especially along the east shore of Lake Huron. One such habitat is the older sand dunes that have become stabilized enough to support some vegetation but not to the extent that trees have become established. Other special habitats are in the depressions or swales between the relatively recently formed dunes near the shore. These provide open sites with sandy but constantly moist or wet prairies and share some of the same rare plants, as well as having some of their own. The rocky shores of the Great Lakes, especially on the north shore of Lake Superior, also support some rare species and populations of species remote from their usual subarctic and alpine ranges. As well as being open habitats in a predominantly forested region, these rocky shores are also characterized by unusual combinations of extreme temperatures. The weather is often cold at that latitude, and cold winds from the lake delay spring. Nevertheless, the microenvironment of the roots may become very warm as the sun heats up the exposed rock. This energy is gradually released from the rock during the night.
Obviously there are many more rare plant species in Ontario than the twelve published on our site. Some, like the dwarf lake iris, have never had extensive ranges. Others have more extensive ranges, but these ranges barely extend into Ontario; these species may still be common in other parts of North America. Still others, like the small white lady's-slipper, have relatively extensive geographic ranges, but have become rare or endangered throughout their ranges as a result of human activity. Human activity, through habitat destruction, is the greatest threat to all of our rare species, here in Ontario as well as in the far-off rain forests.

<< back

^top

next>>