Cacti of Canada

(From Cota-Sanchez, H. 2002. Taxonomy, distribution, rarity status and uses of Canadian Cacti. Haseltonia 9: 17-25)

The cacti of Canada include four taxa: Escobaria vivipara var. vivipara, Opuntia fragilis var. fragilis, O. humifusa, and O. polyacantha var. polyacantha. These species are well adapted to survive the freezing temperatures prevalent during the long Canadian winters.

Although the taxonomic diversity of the Cactaceae in Canada is low, the family is distributed in the central and southern portions of the country, and its west to east range includes the provinces of British Columbia, Alberta, Saskatchewan, Manitoba, and Ontario. The Canadian flora includes four species in two genera: Escobaria Britton and Rose and Opuntia Mill. (Benson, 1982; Scoggan, 1979). These species have developed extreme resistance to cold and represent extreme examples in this typically xerophytic family.

The Northernmost Distribution of the Cactaceae

It is evident that the specialized morphological features in the Cactaceae are directly related to the environment in which they are predominant, i.e., usually arid and semi-arid habitats. However, some species occur beyond what is considered the “normal” ecological environments for the family, such as humid tropical rain forests (where they often grow as epiphytes) and areas of high latitudes (and altitudes) characterized by freezing temperatures. Out of an estimated 20 cold-resistant genera of cacti listed by D’Arcangeli (2002) and Nobel and Bobich (2002), the Canadian cacti are most adapted to withstand cold, harsh winters.
Tolerance to low temperatures varies among cactus species. The most-cold resistant cacti in the Northern Hemisphere are Escobaria vivipara var. vivipara, Opuntia fragilis var. fragilis, O. humifusa, and O. polyacantha var. polyacantha. These exceptional species have evolved to withstand long and extended periods of freezing temperatures, which affect important physiological processes (photosynthesis and respiration) for the survival of the species. The extreme low temperatures that can be tolerated for these species varies from –48°C in O. fragilis -250C in O. humifiusa, -180C in O. polyacantha, and -220C in E. vivipara (Nobel and Bobich, 2002).

The four Canadian native cacti are far beyond the frost line to which most cacti are restricted. The following summary of the distribution of cacti in Canada is based on data compiled from the collections of major Canadian herbaria, namely the Royal British Columbia Museum Herbarium (V), the University of Alberta (ALTA), the University of Winnipeg (UWPG), L’Université de Montreal (MT), the University of Regina (USAS), and the University of Saskatchewan (SASK). The data indicate that Opuntia fragilis var. fragilis is the cactus that reaches the northernmost distribution. Several herbarium specimens collected in the Peace River area in Alberta support the distributional range of this species. According to information obtained from herbarium specimens, the northernmost locality of this species is recorded from the Beatton River, SW of Cecile Lake at 56 17’ N latitude and 120 39’ W longitude. The area of the Peace River system and the environs of the town includes a mixture of cropland, rangeland and pasture in which O. fragilis var. fragilis grows particularly well on hillsides and flat areas with sandy and/or clay soils (Moss, 1994).

Key to Native Cacti of Saskatchewan

(Adapted by J. H. Cota-Sanchez from: Anderson, E. A. 2001.The Cactus Family, Timber Press, Portland, OR and Harms, V. L. 1983. Blue Jay 41: 131-139)

Cactus images used with permission of "Canadian Prairie Wildflowers". These images and many more excellent native plant images are available at the Canadian Prairie Wildflowers Website.

1a. Plants clustering, stem globular, solitary or tufted only from base, tubercles prominent, conical bearing an apical areole with central and radial spines. Areoles hairy; with 3-7 central spines and 12-16 radial spines. Flowers bright pink to violet; perianth parts lanceolate, less than 1 cm wide; outer perianth parts greenish, ciliate-fringed; purplish red; fruit an ellipsoidal smooth, fleshy berry

Escobaria vivipara (Nuttall) Buxbaum (Purple Ball or Pincushion Cactus)

1b. Stems branched, joined into flattened and pad-like segments with constricted joints; spines less than 12 per areole; the areoles with a small series of brown glochids at the base of the spines; flowers borne on the areoles on top of young pads; perianth parts bright yellow; fruit a berry

2 (Opuntia) - see below for species

2a. Plant shrubby, very low growing. Stems segments usually less than 5 cm long to 2.5 cm wide, thick and not strongly flattened, terminal pads detach easily. Leaves (when present) conical to 3 mm long. Areoles 3-6-8 mm apart, with brown to tan glochids and 1-6 barbed spines spreading straight, from 1-3 cm long. Flowers yellowish, sometimes greenish 3-4 cm long to 4 cm in diameter. Fruits ovoid, green or reddish green

Opuntia fragilis (Nuttall) Haworth (Brittle Prickly-Pear)

2b. Plants shrubby with many branches. Stems segments round to broadly obovate mostly over 5 cm long and 3 cm wide, not readily separable. Areoles more distant (8-10 mm apart). Glochids yellow, inconspicuous. Spines 6-10, needle-like 1-2.5 cm long. Flowers yellow, 4.5 to 6 cm long. Fruit ovoid, tan or brown

Opuntia polyacantha Haworth (Plain or Many-Spined Prickly-Pear)

Taxonomic Key to Native Cacti of Canada

(From Cota-Sanchez, H. 2002. Taxonomy, distribution, rarity status and uses of Canadian Cacti. Haseltonia 9: 17-25)

The taxonomic key below is adapted from Anderson (2001), Harms (1983), and McGregor et al. (1986) and includes the major distinctive morphological characters useful in the identification of Canadian cacti.

1a. Plants clustering; stem globular, solitary or tufted only from base; tubercles prominent, conical, bearing an apical areole; areoles hairy, with 3–7 central spines and 12–16 radial spines; glochids absent. Flowers bright pink to violet; perianth parts lanceolate, less than 1 cm wide; outer perianth parts greenish, ciliate-fringed, purplish red. Fruit an ellipsoidal, smooth, fleshy
berry

Escobaria vivipara var. vivipara

1b. Plants low to prostrate; stems branched, consisting of flattened and pad-like segments with constricted joints; glochids present

………………..………………………………………………. 2

2a. Plants creeping. Spines without barbs. Fruit fleshy at maturity, not spiny (but glochids usually present in the areoles)

……...………………......……… Opuntia humifusa

2b. Plants creeping or prostrate. Spines weakly to strongly barbed. Fruit dry at maturity, spine

………………..………………………………………………. 3

3a. Stem segments usually less than 5 cm long to 2.5 cm wide, thick and not strongly flattened, terminal pads easily detached; areoles 3–6 mm apart; glochids brown to tan, conspicuous; spines 1–6, barbed, spreading straight, from 1–3 cm long. Flowers yellowish, sometimes greenish 3–4 cm long, up to 4 cm in diameter. Fruit ovoid, green

…………………………………….O. fragilis var. fragilis

3b. Stem segments round to broadly obovate, mostly over 5 cm long, 3 cm wide, not readily separable; areoles more distant (8–10 mm apart); glochids yellow, inconspicuous; spines 6–10, needle-like, 1–2.5 cm long. Flowers yellow, 4.5–6 cm long. Fruit ovoid, tan or brown

………………………….O. polyacantha var. polyacantha