Eastern prickly pear (Opuntia humifusa, formerly Opuntia compressa)* of the Cactus (Cactaceae) family is a mostly prostrate stem-succulent with large, bright yellow, spectacular flowers. Like most members of its family, the species is adapted to thrive in arid habitats. Interestingly, the cactus family (with the exception of a single species) is native only to the New World. Cactus-looking plants in African and Asian deserts typically belong to either the Spurge (Euphorbiaceae) or the Milkweed (Asclepiadaceae/ Apocynaceae) families.
The genus name, Opuntia, originated in the first century for a cactus-like plant found near Opus, Greece. The specific epithet “humifusa,” from Latin for “spread out,” refers to the plant’s growth habit. Eastern prickly pear, the most widely spread cactus in the eastern U.S., occurs from New Mexico and Colorado east to Connecticut and south across all interior states to the Atlantic and Gulf Coasts. In Arkansas, it occurs across the state except for the Mississippi Alluvial Plain and lower elevations of the West Gulf Coastal Plain. Other common names include devil’s-tongue and common prickly pear.
Eastern prickly pear occurs as scattered individual plants or may form a mat-like colony over time. A succulent species, it is highly tolerant of drought and, unlike most cacti, cold temperatures. It grows well in a wide variety of habitats, varying from full-sun rocky hillside glades and sandy prairies to woodland openings with partial sun. Plants do well in xeric to dry-mesic soils that may range from acidic to alkaline. Plants in areas of encroaching tree cover often die out due to lack of sunlight.
Photo 1: This two-year plant has a round stem at its base and a broadened stem above. With maturity, fewer spines will be present.
Eastern prickly pear is composed mostly of water-storing stems with the lowermost portion being round in cross-section while the remainder of stem comprises thick, flattened, oval to obovate segments (pads or cladodes) that grow chain-like from the upper margin of one pad to the next. Stems to 3 feet long are prostrate, except for terminal pads that may stand up to 8 inches or so. The lowermost portion of the stem extends into soil as a stub from which a few long fibrous roots extend out at shallow depth for several feet. Size of pads is dependent on habitat, but pads may be 5 inches long, 3 inches wide and ½ inch thick. New pads, growing from the distal margins of previous year’s pads, break-off easily and, when in ground contact, can root to form a new clonal plant. The lowest portions of mature plants become woody.
During the growing season, mature pads have a medium green to blue-green waxy, glabrous surface marked by regularly arranged areoles positioned diagonally across both sides of pads and also along upper pad margins. All areoles have tight tufts of short hair-like reddish bristles (glochids) with barbed tips. Areoles on upper sides of pads and along upper pad margin may bear one or two light-colored, stout, needle-like spines to 3 inches long (spines sometimes absent on pads or entire plants). Areoles along upper margins of pads also produce new pads or flowers (see below). Both glochids and spines are painful to human touch; however, the short glochids can be more painful due to their flesh-retaining tips. They are also much more difficult to remove. During drought and with approaching winter, pads lose water content and become thin and wrinkled, but quickly revive with improved conditions.
Photo 2: This plant, which may be four years old, does not have any spines. Note the diagonally arranged areoles with tufts of glochids. Photo in late August.
When new pads develop, side and marginal areoles bear single, short, narrowly conical (subulate) ¼ inch, more or less, vestigial leaves. These leaves quickly drop off, leaving all food-making function (photosynthesis) to the green stems.
In late May into June, solitary flowers grow from areoles along the distal curved margins of previous year’s pads. Multiple flowers may grow from a pad. Early on, flower buds have light green triangular sepals that cover several overlapping series of tepals (sepals transitioning into petals). Flower buds are prominent with a short-conical shape (when seen from side) and are positioned at the tip of inverted-cone-shaped elongate ovaries that are several times longer than buds. Ovaries are glabrous with diagonally arranged, well-spaced, spineless areoles along with a ring of areoles outlining the wide, distal end. The ovarian areoles have the same leaves as new pads, but without spines. Ovaries are slightly ridged.
Photo 3: In this mid-May photo, a previous year’s pad bears a new pad and two flowers growing from areoles at its upper margin. Areoles of new pad bear short conical leaves that will quickly drop off.
At anthesis, the perfect (with male and female parts) diurnal flowers, to 3 inches across, show light to bright yellow overlapping waxy petals. The eight or so petals in the upper series have narrow bases and a broad upper portion with a central point and often two side points. Uppermost petals may or may not be marked by a reddish-orange “flame” that extends upward from the base. Underlying series of petals gradually change shape, grading into the lowermost series. Flowers have numerous short stamens, with light yellow elongate anthers on darker yellow filaments, that encircle a single, white, stout style tipped by a bulbous partitioned stigma.
Photo 4: This orange-centered flower has three points on its petals. Triangular green sepals can be seen on the bloomed-out flower to the right. A young pad behind this flower still bears its small conical leaves.
Spent flowers quickly fall from the ovary (developing fruit), exposing a concave scarred upper surface. As the elongate fruit (berry) matures, it becomes fleshy and purplish. Fruits remain on the stem into the next growing season. Fruits contain 20 to 30 light colored, flattened and circular seeds that have an indentation on one margin and a protruding edge all around. Seeds are dispersed by small mammals and birds.
Photo 5: Central pad bears five flowers and no new pads. Light colored lines across old pads may result from pad shrinkage during winter or droughts. Photo in early June.
Photo 6: In this early January photo, the two fruits are 2½ inches long and ½ inch in diameter. Inset shows seeds in a fruit as well as three cleaned seeds that bear imprint of embryonic plants.
In a garden setting, eastern prickly pear may be suitable for xeriscape and rock gardens where the plants could remain untouched and where other vegetation would not invade the area. Plants can be easily started by setting the end of a detached pad at the chosen permanent site. Eastern prickly pear is a dependable bloomer. Fruit and pads of prickly pears are edible and may be found in grocery stores labeled “nopalito” (pads) and “tuna” (fruit). However, care must be taken to remove the glochids from pads of our native species.
Along with eastern prickly pear (Opuntia humifusa), a second native cactus occurs in Arkansas, namely, western prickly pear (Opuntia macrorhiza)*. This second species is recorded from scattered counties in the Interior Highlands. Opuntia macrorhiza, also known as plains prickly pear, has more than two spines per areole, with spines occurring in areoles across the entire pad surface. It is also sometimes reported to have thicker, tuberous roots in comparison.
*The taxonomy of the genus Opuntia is widely debated. The treatment presented here follows the traditional (and most simplistic) view of Arkansas prickly pears. However, some authorities believe we have several additional species within the state, but delineation of those species and the most appropriate application of names to those species is not settled. Some of those authorities believe we do not have true Opuntia humifusa in Arkansas, this being a species more confined to the Northeast. The name Opuntia cespitosa may sometimes be found applied to the common prickly pear in Arkansas traditionally called Opuntia humifusa. To make things even more confusing, hybrids have been reported within the genus.
Article and photographs by ANPS member Sid Vogelpohl
Arkansas Native Plant Society 