Opuntiads of the USA

Skip the introduction; jump to the list of cactus species and photos.

Opuntia macrocentra, by Dave Ferguson

This Web site is for people interested in Opuntia and their relatives, the opuntiads. They are fascinating plants naturally found in many parts of the continental USA. Opuntia are scattered irregularly and far apart in the Northeast and upper Great Plains, but sometimes are so numerous that they create cactus forests in Texas and more westerly states. This Web site is designed to introduce some of the species that are native to continental United States. Additionally, a few other cacti, and other xeric plants will also be described.

Opuntia and related species are found from Canada to southern Argentina and Chile, and are one of the most successful cactus groups in terms of biomass, habitats conquered, and geographic distribution. Their flowers are often large and colorful, but they may be delicate in color. Their fruits and cladodes are consumed by animals and people in many countries, and the plants serve as barriers and landscape items for many people.

Opuntiads are characterized by their jointed stems, which may be flat or cylindrical. Platyopuntias have flattened stems called cladodes. The cladodes function as photosynthetic organs; the pads are not leaves. Like most stems, cladodes have shoots and leaves and can bear branches and flowers. Platyopuntia leaves are small and short-lived, typically falling off when the shoot is young. Such leaves may be just an eighth of an inch long and not noticed by the casual observer because their time on the plant is short. Alternately, some opuntiads may have leaves 2 or 3 inches long that can last many months on the plant.

In contrast, cylindropuntias also have modified stems that serve as photosynthetic organs, but these are cylindrical and not flat. Cylindropuntia genera include Cylindropuntia, Tephrocactus, and Austrocylindropuntia. Other opuntiads may have club-shaped cladodes (eg, Grusonia), or semi-spherical cladodes (Cumulopuntia).

Another characteristic of opuntiads is the presence of glochids at areoles. Glochids are small spines that can cluster in great numbers at areoles.

In the wrong place Opuntia can be destructive weeds; they can overrun cattle grazing lands or displace native plants. In the Americas and other continents they may be serious pests. In addition to ruining grazing areas, Opuntia may also out compete certain native plants and thereby upset ecosystems. Opuntia have some of the nastiest spines (including glochids) found in cacti. Glochids are tiny spines that may appear hair like; they are smaller than typical spines and are produced in areoles along with "regular" spines. An unfriendly encounter with an Opuntia can leave a lasting bad memory.

The emphasis herein is on plants that have the beaver-tail look because this group of opuntiads is the most numerous in the USA. However, other opuntiads are described as well because they are interesting or because they used to be treated as members of the genus Opuntia.