Western Prickly Pear

Several species of prickly pear are probably growing in the reserve. The most common appears to be the western prickly pear (Opuntia x occidentalis), a naturally occurring hybrid of three species usually found in openings in the coastal sage scrub. Despite the fierce spines, the blades and fruit are important food for Native Americans, and the pads (nopales) and fruit (tunas) can also be found in Mexican markets and restaurants.

Prickly pear hosts a variety of herbivorous insects and predatory spiders. In October, the Spider Condominium west of the Nature Center is a popular station for Family Fun Days.

Description ^2,4,23,26,59

Our prickly pear is a multi-stemmed, sprawling plant, often forming an impenetrable mass up to 5 feet (1.5 m) high and 20-30 feet (9 m) wide. The genus is variable and many hybrids are known to exist.

The plant consists of broad, flat pads or segments, which are modified stems. The green or bluish-green pads are oval or ovate and usually less than 14 inches (36 cm) long and 10 inches (25 cm) wide.  Clusters of 2-6 or more sharp spines of varying lengths arise from regular points on the surface of the pads (areoles). The long spines lack terminal barbs.  At the base of a long spine, there is a tuft of short, fine, barbed spines (glochids) that, when mature, detach readily from the areoles, penetrating easily and annoyingly.

Leaves are short-lived but occasionally seen on young segments. They are short, conical and fleshy.

Showy yellow flowers appear on the edges of the pads in May and June.¹ Petals and sepals are identical (together called tepals). There are 9-10 petal-like yellow tepals; often tinged with red. The outer edge of a tepal is irregular and may have a central notch. Stamens are numerous (> 200) and yellow. These surround the pistil that is topped with 10 or fewer greenish stigmas that resemble inward curving fingers.

The edible, egg-shaped fruit is red, sweet and fleshy.  Long spines are absent, but tufts of glochids are present.

Classification ^2,59

Western prickly pear is a dicot angiosperm in the cactus family, Cactaceae. Members of this family are characterized by succulent stems that contain chlorophyll and by spines that have evolved from leaves.⁴⁴ With one possible exception, Cactaceae evolved in the New World. Three cactus have been reported from the Reserve: coast barrel cactus (Ferocactus viridescens), coast cholla (Cylindropuntia prolifera) and the coast prickly pear (O. littoralis).⁴⁸

Opuntia species are distinguished from other cactus by their flattened stem segments,² and by the presence of glochids, tufts of very small, penetrating spines found at the base of the larger spines. The closely related chollas, which have rounded stems, were originally placed in this genus, but are now in the genus Cylindropuntia.

At the time of writing (June 2014) a single species of Opuntia has been reported from the Reserve, O. littoralis.⁴⁸ However, most of the prickly pears in the Reserve have pads that are too large to be that species. The plants that we have examined (from the Santa Inez trailhead, below the Santa Helena trailhead and the Nature Center) key to O. x occidentalis, a three-way hybrid between O. engelmanii x O. phaeacantha and O. littoralis.²  However, not all characteristics of our plants match the written descriptions. To further complicate matters, most of the native coastal prickly pears may have hybridized to some extent with the mission fig (O. ficus-indica) introduced by the early settlers for food.⁹⁶ It is unlikely that a mere mortal will untangle our plant species without genetic information.

Ecology ^60,96

Like most cacti, prickly pears are highly adapted for dry climates. Leaves are small and rarely present. Instead, the thick, waxy stems (pads) have developed chlorophyll and assumed the photosynthetic function of leaves. The internal tissues of pads are spongy, providing a large volume for storing water. The root system is shallow and extensively branched, allowing prickly pears to capture even the slightest moisture. The spines, which protect the cactus from small rodents that would chew the pads for moisture, also serve as dew points; the largest spines, which often tend downward, condense fine mist and dew and direct the resultant dew drops to the roots at the base of the plant.

In addition, cactus have evolved “Crassulacean Acid Metabolism” (CAM). Almost all plants take up carbon dioxide and release oxygen during the day when the CO₂ can be immediately used for photosynthesis. Most water loss occurs during this exchange of gasses. With CAM, cacti are able to exchange gasses at night, temporarily storing CO₂ in an acid form. Since gas exchange occurs when the temperature is lower and humidity higher, the inevitable loss of water is reduced. It is estimated that cactus lose 1/6000 ^th as much water as an average plant. This type of metabolism was first identified in the family Crassulaceae, which includes succulent plants such as jade plants and sedums. It is found in a wide variety of other plants, such as agaves, orchids and pineapples.⁴¹

Cactus flowers are designed to ensure cross-pollination. The top of the female reproductive structure, the stigma, extends above the male stamens, providing a landing place for pollinators that deposit pollen from recently-visited plants. To collect nectar and additional pollen from the target flower, the insect burrows through the pollen-loaded stamens to the nectar chamber. The stamens are thigmotactic, reacting to touch by closing inward around the insect, thoroughly dusting it with pollen. Some of this pollen will be deposited on the next flower visited.

Human Uses  

Prickly pears were used for food by Native Americans and continue to be important today. Kumeyaay, Luiseño, and Chumash relished the juicy red fruits, either fresh or dried for later use;^16,17,15 the Kumeyaay fried or boiled the pads¹⁶. In either case, the spines and troublesome glochids were knocked off, by rolling the cactus piece around on the ground or by brushing, often with coyote brush. Today, Mexican markets and restaurants offer the fruit, “tunas” and young pads “nopales” in a variety of ways.⁶²

Prickly pears have been and are used for a variety of other purposes.⁶² The Chumash made paint from the red juice of the fruit and improved the water repellant qualities of plaster with juice from the pads;¹⁵ the Kumeyaay used the long spines for applying tattoos, using charcoal as the pigment.¹⁰⁰ Early settlers used a cut pad for a black eye.³² Modern Kumeyaay make a tea as a treatment for diabetes.¹⁸

Prickly pears are important as cattle food, and often provide the only forage for range cattle during dry spells. In the early 20th century, Luther Burbank developed several varieties of spineless cactus for this purpose.⁶²

Interesting Facts  

Prickly pears in the Reserve support a variety of spiders such as the silver argiope, the dew-drop spider and at least one species of funnel weaver. Frequently encountered insects include cactus bees and prickly pear bugs (Narnia femorata, a type of leaf-footed bug).⁵⁹ The Spider Condominium west of the Nature Center is a favorite stop for docent tours and during Family Discovery Days.

Prickly pears also host the cochineal scale (Dactyliopis spp.),⁵⁹ which, like other scales, attaches itself to the plant and sucks its juices. Dactyliopis spp. infect only species of Opuntia. The insects are hidden and protected by a waxy white substance which resembles tufts of cotton. The scales contain red carminic acid, thought to be distasteful to predators. The Aztecs learned to make a brilliant crimson dye from the carminic acid, and when the Spaniards arrived they found extensive farms of prickly pears and the associated scales. Cochineal quickly became an important export for European markets, second only to silver in export value.

In an attempt to get a piece of the cochineal “action” Australians introduced several species of prickly pear to their country.²⁸⁵ The cochineal industry never developed, but the prickly pear exploded throughout eastern Australia; by 1920, 58 million acres had been destroyed by the non-native cactus. The cactus was finally controlled by the introduction of a small moth whose caterpillars feed on the prickly pear.  For a “rollicking history” of the rise and fall of the color red and the role of the cochineal scale, read “A Perfect Red: Empire, Espionage and the Quest for the Color of Desire” ⁶¹ or a shorter article based on it that is available online.¹⁹¹