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Recovery Strategy for the Eastern Prickly Pear Cactus (Opuntia humifusa) in Canada

3. Description of the Species and its Needs

3.1 Eastern Prickly Pear Cactus Description

Eastern Prickly Pear Cactus is a perennial, low, spreading, succulent cactus with jointed, rounded, but flattened, green stems measuring 5 to 12 cm in length. Stem segments are fleshy or firm and become wrinkled under drought stress. Stems are sparsely covered with clusters of barbed bristles and spines. It has a shallow, efficient root system consisting of a central taproot and fleshy, lateral roots. Flowers appear in June. They are large, waxy and yellow with red centres. The fruits are oblong and turn red when mature. Eastern Prickly Pear Cactus occurs as small patches or large scattered colonies of thousands of stems. For more detailed information on this species' description please consult Benson (1982).

3.2 Eastern Prickly Pear Cactus Needs

Eastern Prickly Pear Cactus can survive across a wide range of environmental conditions as it is highly drought tolerant and has low nutrient requirements. In Canada, the species is limited to dry, sandy substrates, typically near shore dunes and sand barrens, that are in the early stages of succession (Reznicek 1982, Klinkenberg and Klinkenberg 1984, Chiarot 1992). The species is associated with the Lake Erie Sand Spit Savannas ecosystem. This ecosystem includes habitats along the shorelines of Lake Erie sand spits and in the dry interior areas of these sand spits (dry Open and Shrub Shoreline; Open, Shrub and Treed Sand Dune; Tallgrass, Mixed Tallgrass and Coniferous Savanna and some Coniferous and Mixed Woodland vegetation communities) that are characterized by the presence of semi-open, early successional vegetation situated on well-drained, nutrient-poor, sandy substrates (Geomatics International Inc. 1994). Together, these habitats share biophysical attributes and are subject to comparable geophysical processes. The more open of these habitats (Little Bluestem-Switchgrass-Beachgrass Open Graminoid Sand Dunes, Hoptree Shrub Sand Dunes and Red Cedar Treed Sand Dunes) support, or are capable of supporting, Eastern Prickly Pear Cactus. However, relict plants can be found in later successional stages of thicket, woodland and forest.

This species is limited by light exposure conditions. Optimal growth occurs with 50 to 70 percent lighting (VanDerWal et al. 2007b), while full light may result in rapid drying of the sandy soils, contributing to reduced vigour. Seedlings survive best in more open primary and secondary successional habitats.

Eastern Prickly Pear Cactus relies on bumblebees and other bee species for pollination (Kevan and Aiello 2002) and on birds and mammals for seed dispersal. It may be limited where pollinators and dispersers are in short supply or where unsuitable habitat (e.g. forests) acts as a barrier to pollinator movement (Kevan et al. 2003).