• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS:

Plains prickly-pear is a perennial, typically reaching 4 to 12 inches (10-30 cm) in height and rarely growing more than 16 inches (40 cm) tall [42]. The glabrous, flattened stems are 2 to 4 inches (5-12 cm) broad, 2 to 5 inches (5-13 cm) long, and about 0.4 inches (1 cm) thick. Spines of these stems are only slightly barbed. The species tends to form clumps or mats that extend several yards in diameter [6,42]. Mats up to 12 feet (3.7 m) in width and 30 feet (9.15 m) long were observed in the Great Plains [104].

The fruits are dry at maturity and are covered with barbed spines. Fruits develop on stem lobes. An examination of 550 randomly selected branches revealed fruit on 32% of the stem lobes, varying from none to 5 fruits per lobe. The most fruit is produced on stem branches that are 6 to 8 years old. The number of seeds varies from none to more than 70 per fruit [97]. Seeds are flat, and about 1.5 to 3.5 mm thick [70].

Plains prickly-pear has a shallow, laterally extensive root system that takes advantage of rainfall as scant as 2.5 mm. Its high water retention capability in aboveground tissues allows it to survive drought. A clump 1 foot (0.3 m) in diameter may have a root system 4 to 6 feet (1.2-1.8 m) in diameter [17,22,71,97].

Opuntia plants usually live less than 20 years, but vegetative propagation can ensure a very long life span for the clonal colony [93].

RAUNKIAER [75] LIFE FORM:

Stem succulent

REGENERATION PROCESSES:

Plains prickly-pear reproduces by seeds, layering, and sprouting from segments mechanically separated from the parent plant. Stem die-back in mature clumps can separate the plant into several individuals [56,70,97]. Detached stems buried in soil or litter may grow horizontally before sprouting [6,38,62,71,97,103]. Root sprouting has been documented in diploid populations of Opuntia polyacantha var. polyacantha in New Mexico [38,70]. Root sprouting may occur in other Opuntia polyacantha populations and  infrataxa, but is poorly documented in the literature and in herbaria specimens [70].

Following a severe July hailstorm in northeastern Colorado, researchers quantified the number of plants that established from the many broken and scattered stem segments. In a pasture with an original plains prickly-pear ground cover of 1.2%, the hail detached an estimated 1,660 segments/acre (4,100 segments/ha). In another pasture that had 3.3% plains prickly-pear ground cover, 7,700 segments/acre (19,100 segments/ha) were detached by the storm. By August of the following year, 1,400 and 2,400 of the segments had rooted, respectively, in the 2 pastures [56].

Seeds of plains prickly-pear fall near the parent plant or are dispersed by mammals that consume the fruits. They are also dispersed when barbs on the fruits or lobes attach to a passing large mammal [45,48,93,97,103,104]. Information on seed longevity was not found.

Seedling growth was measured for 3 years in 22 field plots in northeastern Colorado. By the end of the 3rd growing season plains prickly-pear seedlings were only 2.5 to 3 inches (6-8 cm) in length. The diameter of well-developed clumps may increase 3 inches (8 cm) annually. Plains prickly-pear clusters 3 feet (0.9 m) in diameter may take as much as 15 years to develop [97].

SITE CHARACTERISTICS:

Plains prickly-pear occurs on dry sites in 22 central and western states and provinces. It is common in the Great Plains, Great Basin, and Southwest [,6,45]. Plains prickly-pear occurs both on grazed ranges and in areas not used by livestock [38,97]. It occurs in disturbed roadside areas [63] and in old, relict, pre-agricultural plant communities [3,25]. It is found on clay loam and sandy loam soils but is infrequent on sand dunes. In grasslands, prickly-pear does not occur in areas characterized by abundant soil moisture, such as swales and depressions. Its frequency decreases in wet years. Precipitation is a primary determinant of the distribution and abundance of plains prickly-pear [76,97].

Plains prickly-pear was classified in a Utah salt-gradient study as having a low tolerance to salt [86], but a survey of saline areas (visible salt crystals on the soil surface) in southern Alberta and Saskatchewan revealed that plains prickly-pear was present on more than 11% of the sites [11].

Throughout its range, plains prickly-pear occurs from as low as 1,000 feet (300 m) in the Great Plains [83] to at least as high as 8,000 feet (1,600 m) in the southern Great Basin [6].

Elevations reported in the literature are as follows:

4,300 to 7,500 feet (1,310-2,285 m) in Colorado [25,40]
2,250 to 5,700 feet (685-1,735 m) in Montana [61,83]
4,920 to 6,560 feet (1,500-2,000 m) in Utah [31]
1,000 to 5,000 feet (300-1,525 m) in the northern Great Plains [83]
1,000 to 8,000 feet (300-2,440 m) in the southern Great Plains [6,83]

SUCCESSIONAL STATUS:

Although plains prickly-pear is present and often abundant in climax or late-successional communities throughout its range [3,25,37,103], it is often regarded a disturbance-adapted, early seral species [83]. It increases in number in response to disturbances such as drought [103], grazing pressure [79], and severe hailstorms [56]. Plains prickly-pear cover decreases as precipitation normalizes following drought [45,97,103].

SEASONAL DEVELOPMENT:

Fruits ripen approximately 2-1/2 months after flowering [70]. The phenology of plains prickly-pear over a 1-year period in northern Colorado was as follows [64]:

Pads regreening	March
Pads enlarging	April
Floral buds developing	May
Flowering	June/July
Fruit developing	July/August
Fruit drop	September

Plains prickly-pear showed a decline in carbohydrate reserves throughout winter quiescence, regreening of pads, and flowering, with a low point reached at the end of flowering. A maximum in the root carbohydrate reserves was found at fall quiescence [64].

In a southern Colorado study site, plains prickly-pear bloomed for 21 to 28 days, beginning in late May. Individual flowers were open from 7-11 hours per day [68].

Flowering generally occurs from June to July in Montana and North Dakota [21].

Related categories for SPECIES: Opuntia polyacantha | Plains Prickly-Pear