Part 1 COSSARO candidate species at risk evaluation form – June 2010

Eastern Prickly Pear Cactus (Opuntia humifusa)

Current designations:

GRANKG5 (NatureServe 2010)
NRANK Canada – N1 (NatureServe 2010)
COSEWIC – Endangered (COSEWIC 2010a); originally designated by COSEWIC as Endangered in 1985, and has remained as such in each subsequent review (1998, 2000, 2010)
SARA – Endangered, Schedule 1 (Species at Risk Public Registry, 2010)
General Status Canada – At risk (Wild Species 2005)
ESA 2007 – Endangered, O. Reg. 72/10
General Status Ontario – At risk (Wild Species 2005)

Distribution and status outside Ontario:

Eastern Prickly Pear Cactus is widespread in eastern North America, occurring in 35 states, from Massachusetts and Florida west to South Dakota and Texas. It is more abundant in the southern parts of its range. In the northernmost states in which it occurs (Massachusetts, Rhode Island, Connecticut, Pennsylvania, Ohio, Wisconsin, and Iowa), it is relatively rare, being ranked as S1 or S3 (COSEWIC 2010a).

Eligibility criteria

Native status

✔ [yes] Although there are several populations in southwestern Ontario that clearly are introduced, there are two populations for which no questions have been raised regarding their natural occurrence.

Taxonomic distinctness

✔ [yes] Eastern Prickly Pear Cactus is a distinct species; Opuntia humifusa var. humifusa is the only variety that occurs in Ontario.

Designatable units

One. The species occurs only in the Carolinian region (Ecoregion 7E) in Ontario.

Priority-setting criteria

Recent arrival

✔ [no] There is no evidence to suggest that the species has arrived recently, or that it was introduced by aboriginal people for medicinal purposes; it was first discovered in Ontario on Long Point in 1883 by John Macoun (COSEWIC 2010a).


✔ [no] Immobile; resident in Ontario.

Primary criteria (rarity and declines)

  1. Global rank

    ✔ [not in any category]. G5.

  2. Global decline

    ✔ [not in any category]. No evidence of global decline.

  3. Northeastern North America ranks

    ✔ [not in any category]. S1, S2, SH, or SX in 21% of its northeastern jurisdictions.

  4. Northeastern North America decline

    ✔ [not in any category]. No evidence of northeastern North American declines, although its habitat is threatened in many places.

  5. Ontario occurrences

    ✔ [Endangered]. Only two natural (non-introduced) occurrences in Ontario (three, if Point Pelee is treated as being two distinct populations)(an additional five occurrences are known to be introduced; COSEWIC 2010a).

  6. Ontario decline

    ✔ [Special concern]. One of three populations (33%) appears to have disappeared since historic times (the Long Point population has not been seen since the 1950s; COSEWIC 2010a).

  7. Ontario’s conservation responsibility

    ✔ [not in any category]. Ontario’s portion of the species' range constitutes less than 1% of its overall range.

Secondary criteria (threats and vulnerability)

  1. Population sustainability

    ✔ [not in any category]. There is no evidence of recruitment failure, nor has a formal Population Viability Analysis been conducted. There is some unquantified evidence that habitat is diminishing, but this element of sustainability is dealt with in the "Direct Threats" criterion below.

  2. Lack of regulatory protection for exploited wild populations

    ✔ [not in any category]. Both Ontario populations are contained within regulated protected areas, and therefore, receive protection under the National Parks Act or the Provincial Parks and Conservation Reserves Act. The species is regulated under both the federal Species at Risk Act and the provincial Endangered Species Act, as well.

  3. Direct threats

    ✔ [Endangered]. Most cacti are subject to horticultural collecting, but this taxon tends to be weedy and abundant at many localities within its American range, and it is resilient to collecting activity there (NatureServe 2010). However, it is neither abundant nor weedy in its Ontario locations. Nevertheless, the risk from collecting should also be minimized because of the regulatory tools that are in place.

    Habitat loss through successional processes coupled with restriction of natural disturbance regimes (disruption of natural coastal sand accretion processes due to shoreline obstructions such as piers, coastal erosion, including ice scouring, fire prevention, etc.) is a primary threat (COSEWIC 2010a). At both extant native locations (100%), the populations are subject to "imminent [and] or projected reduction in habitat quality owing to lack of … implementation of appropriate species-specific management measures", which has and will continue to result in invasion by competitors from later seral stages (COSSARO criteria).

    In both native populations, but particularly in the larger population at Point Pelee, there is an ongoing and relatively long-standing threat of trampling from park users on unauthorized seasonal trails, as well (COSEWIC 2010a).

  4. Specialized life history or habitat-use characteristics

    ✔ [Endangered]. Fish Point population is in Red Cedar Dune Savannah (S1) and Dry-Fresh Hackberry Deciduous Forest (S2); Point Pelee population is in Little Bluestem – Switchgrass – Beachgrass Dune Grassland (S2), Hoptree Dune Shrubland (S1), and Red Cedar Dune Savannah (S1) near the shore, and Dry-Fresh Red Cedar Coniferous Woodland, Dry Sand Dropseed Open Sand Barrens, and former agricultural lands that have succeeded into graminoid and mixed meadows, in interior locations.

COSSARO criteria met (primary/secondary)

  • Endangered – [1/2]
  • Threatened – [0/0]
  • Special concern – [1/0]


The Eastern Prickly Pear Cactus is one of two native cacti in Ontario, and the only one that is presently considered to be at risk. It occurs as a native species in sandy, open to partly shaded habitats in two locations at the western end of Lake Erie, although it is known from a small number of additional sites as an introduction. The major risk factors at these locations include habitat loss and/or degradation due to vegetation succession, shoreline erosion, and the elimination of natural disturbance regimes that would refresh the habitats upon which it depends. Restoration of its habitat is technically feasible, but only limited actions have been taken at these locations, to this point. One population is very small, while the other has over 2000 individuals, but the factors leading to habitat degradation could lead to reductions in numbers in the larger population, as well. This species remains Endangered in Ontario.

Information sources

COSEWIC. 2010a. Update COSEWIC status report on Eastern Prickly Pear Cactus, Opuntia humifusa. COSEWIC, Ottawa. 40 pp.

NatureServe. 2010. (updated to 2 February 2009; accessed on 28 May 2010).

OMNR. 2010. Ontario Ministry of Natural Resources, Species at Risk website.[]. Accessed April 2010.

Species at Risk Public Registry. 2010. []. Accessed April 2010.

Wild Species. 2005. General Status Search Tool. []. Accessed April 2010.

Appendix 1

Northeastern North America rank, status and decline

LBNot present
MBNot present
MENot present
NBNot present
NFNot present
NHNot present
NSNot present
PENot present
QCNot present
VTNot present
  • Occurs (or occurred) as a native species in [19] northeastern jurisdictions SRANK or equivalent information available for [11] of [19] jurisdictions = (58%) S1, S2, SH, or SX in [4] of [19] = (21%)

Part 2 Ontario evaluation using COSEWIC criteria

Regional (Ontario) COSEWIC criteria assessment

Criterion A – declining population

No (N/A). Although declines are suspected, the evidence suggests otherwise, probably due to altered but more rigorous survey protocols.

Criterion B – small distribution and decline or fluctuation

Yes (Endangered; B1ab(iii) and B2ab(iii)). Only two native populations occupying a very small extent (63 km2)and area (16 km2) are known in the province, and habitat quality and quantity are expected to continue to decline unless habitat management interventions occur.

Criterion C – small population size and decline

Yes (Endangered; C2a(ii)). One population contains over 95% of the individuals, and future decline is inferred through continued loss or degradation of habitat.

Criterion D – very small or restricted

Yes (Threatened; D2). There are fewer than 5 populations and the AO <20 km2.

Criterion E – quantitative analysis

No (insufficient information). No PVAs or other quantitative analyses of persistence have been conducted.

Rescue effect

No. This species is rare in most jurisdictions near southwestern Ontario. In addition, it is not adapted for long-distance dispersal.