Cactus can survive our harsh winters

By Neil Gushulak
Biologist

Brittle Prickly Pear Cactus
Opuntia fragilis fragilis
There are four species of cactus and one hybrid that occur naturally in Canada. Most species are restricted to the western provinces as the soils are loose and temperatures are warmer than the Rainy River area. Of the five species found in Canada, one can be found around Rainy River in Lake of the Woods. These tiny cactus are found on many of the islands in Lake of the Woods, from the Bergland area north to the Northern Peninsula around Kenora. There are approximately 12 known localities where they can be found in Lake of the Woods.
Brittle Prickly Pear cactus are found from Ontario to British Columbia in Canada, south to the northern parts of the California, New Mexico and Texas. This species has a very large distribution and is the most northern species of cactus in the world, occurring north to the Peace River area in British Columbia. They are most common in the southern Prairie Provinces in Canada and Lake of the Woods is as far east as they naturally occur. There is a single record of this species in eastern Ontario around Kaladar, near Ottawa. This population is isolated and genetically unique and may be introduced.
Brittle Prickly Pear cactus are identified easily by their small size. They are a mat forming species and rarely grow larger than 10cm in height, although many populations may cover many square meters. These cactus have small pads, nearly oval in shape and are about 6 cm in length. They are covered in small spines, growing in clusters of 1-4; spines are typically white or brownish depending on the population and are approximately 5cm in length. In addition to spines there are many small whisker like spines called gloccids which are at the base of the spines. They are typically found on south facing islands in Lake of the Woods, usually about 10m from the water edge. In the Canadian Shield topography of Lake of the Woods these cactus are typically found in rocky fissures and cracks, they root readily when detached. Although these cactus produce beautiful yellow flowers in the early summer, most seeds are sterile. This species has adapted almost complete to asexual reproduction. As their Latin name suggests, they are fragile and the pads easily detached. Most are carried away by animals and will fall off and root in other areas. Because the pads float readily, many are transferred by water bodies; they may float for weeks before finding a suitable area to root. The populations of this cactus in Lake of the Woods and the Whiteshell area of Manitoba are thought to be distributed by the early fur traders of the region. The cactus found in the Whiteshell and Lake of the Woods areas are typically very tiny, pads are rarely longer than 3cm, the spines are greatly reduced and small. Further west in Manitoba this cactus produces much larger pads and have very large spines.
Although most desert cactus species can tolerate temperature as low as -10C, Opuntia fragilis can survive temperatures as low as -45C. I have kept this species in outdoor cactus gardens and they have survived temperatures as low as -47C. They are the most cold tolerate of any cactus species in the world. They grow explosively in the warmer months, by the fall they lose most of their water content, shrivel and appear dead. Most species found in our region are typically found in small patches of suitable habitat almost always on the islands.
The Rainy River area is blessed with a great diversity of animal and plant life, many local residents are unaware that cactus naturally occur in this area as most people associate cactus with deserts. The Brittle Prickly Pear cactus is one of the most interesting and unique plants found in our area.