Milwaukee Public Museum

by Neil Luebke

EDITOR'S NOTE: This article is reprinted from LORE magazine, a benefit of museum membership. ©1996 Milwaukee Public Museum, Inc.

Just what is a cactus? It's more than a plant with stickers. To a botanist it is a plant that has certain characteristics that place it in the family of plants known as the Cactaceae. A unique feature of cacti are areoles, small areas on the stem which contain spines. Areoles are also the places where flowers, new stems, or roots arise. A cactus is a perennial, that is it can live for many years. Most cacti are without leaves. The stem is fleshy or succulent and contains water-storing tissue. These features allow the plant to withstand periods of drought, which is a common occurrence in the habitats where cacti grow. All cacti can be called succulents, but not all succulents are cacti. In addition to the Cactaceae, succulents occur in the lily, milkweed, daisy, stonecrop, and about 45 other plant families.

The vast majority of cacti live in desert and semi-desert habitats. But they can also be found in jungles as well as other habitats that receive above desert rainfall. Although cacti have been planted in suitable climates around the world, cacti are almost exclusively native to the Americas. They range from the Patagonia region of South America north into Canada. Only the tree-perching species of Ripsalis occur naturally in Africa, the Muscarine Islands, and Ceylon. However, even there are believed to be of American origin. The question as to how many different kinds of cacti there are is open to debate. Estimates vary from 800 to about 2,000 species.

In the United States, cacti occur naturally in all states except Hawaii, Alaska, Vermont, New Hampshire, and Maine. Wisconsin's three species of cacti are Prickly Pears (Opuntia spp.). They occur on the well-drained sandy or gravelly soils in the southwestern and central part of the state. The areas richest in cacti in the United States extend east from southern California through Arizona and New Mexico to central Texas.

In the southwestern United States one sees some of the fascinating forms cacti have evolved into as they have adapted to an arid and generally hostile environment. Survival in such places has meant a no frills plant, stripped down to the bare essentials to conserve water.

One of the largest cacti is the Saquaro or Giant Cactus (Cereus giganteus). Attaining tree-like heights of up to 50 feet, the candelabra appearance of the Saguaro is the dominant feature of the Arizona Desert. Some Saguaros are estimated to be 200 years of age. Also prominent in the landscape are the tall columns of the Organ Pipe Cactus (Cereus thurberi), a large shrubby plant with many branches reaching 20 feet in height. Closely related to the Saguaro is Cereus peruvianus, the choice of landscapers in warm, dry regions and of interior decorators throughout the country. This is the tall, columnar cactus that is often planted two to the pot and which is sold by florists. In its native South America, it is often a multi-branched plant which can reach 40 feet in height.

Resembling small trees or shrubs, Jumping and Teddy Bear Chollas (Opuntia fulgida and O. bigelovii) are common throughout the grassland deserts of the Southwest. While teddy bear is a rather benign descriptive name, Jumping cholla comes closer to revealing the true nature of these cacti. Armed with numerous spines, they readily separate at a joint and attach themselves to anything that brushes against them. Any encounter with a cholla is a painful experience. Chollas also freely drop stem segments to the ground where they put out roots and grow into new plants, an adaptation that allows the chollas to quickly reproduce in an unfriendly environment.

Perhaps the most wide ranging cacti are the low mat-forming Prickly Pears (Opuntia spp.) with flattened stems or pads. while they are very adaptable to many different growing conditions, they are not a favorite of hobbyists because of the many cushions of small barbed bristles on their flattened stems or pads. These bristles are more irritating than the larger spines. Still they are the most economically important group of cacti. In some areas they are grown for their edible pear-shaped fruits called tunas, prickly pears or Indian-figs. Prickly Pear pads have even been used for cattle feed in arid regions, after burning off the spines. The famous plant breeder Luther Burbank worked with Prickly Pears to develop a "spineless cactus" to be used as a forage crop. They have also been used to prevent soil erosion. However, when introduced into South Africa and Australia, they soon became a serious weed in large areas of pasture land, and vast sums of money have been spent by governments trying to eradicate them.

Of more interest to growers of cacti are the globular shaped Barrel Cacti (Echinocactus spp., Ferocactus, spp. and their relatives). The Barrel Cacti have earned a reputation of being an emergency water resource for desert travelers. However, the juice from the pulp varies from species to species. Some contain water that is drinkable while others are reported to contain juice that is slimy and nauseating, and best drunk only as a last resort.

Cacti of the Southwest exhibit what seems to be an endless array of variation. The Mammillarieas are small, compact mounds of spines that do well as potted plants. The Living Rock Cacti (Ariocarpus spp.) of Texas resemble weathered rocks with their rough, fissured appearance. Only a true aficionado of cacti sees beauty in these. The Button Cacti, such as Peyote or Mescal Buttons (Lophophora williamsii) appear as smooth, grayish green spheres. Peyote is the "communion" to many North American Indians. Because of its hallucinogenic properties it is considered a drug plant and is off limits to U.S. growers.

Surprisingly, the array of variations and forms seems limitless for a plant so pared down by nature to survive the extremes of its environment. Not to be overlooked is the beauty cacti exhibit in their symmetry of form as well as in their brightly colored flowers. Little wonder that cacti are popular with houseplant enthusiasts.

It is also easy to understand why cacti took Europe by storm when they were first introduced there by the early Spanish explorers. These strange, exotic plants, once thought to be related to thistles, could only be afforded by the wealthy. Today, most are within reach of all.

In addition to being great looking plants, they are relatively easy to grow. Most will exist with neglect but thrive when given good care. These are plants well adapted to the dry conditions found in the home and many are able to de well with only moderate amounts of light. Not all require the high light levels cacti are generally thought to need.

As houseplants they aren't very demanding. A loose, fast- draining soil moisture is generally thought to be best, since plants won't tolerate wet soil for long periods of time. A mixture of topsoil or loam, sand or perlite, and leafmold or peatmoss with a little bonemeal works well. Organic matter should be less than 20% of the total bulk except for the epiphytic cacti such as Christmas, Easter, and Orchid Cacti which prefer more organic matter, more moisture, and less light than many of the terrestrial cacti.

When plants are watered, the soil should be thoroughly soaked, especially during the growing season. Frequency of watering varies with the mixture of potting soil, types of pot, and time of year. Plants in heavy soil, plastic pots, or during the winter, should be watered less often than plants growing in light, porous soil, clay pots, or during the growing season.

Cacti are slow growers. Fertilizers should be used sparingly except for epiphytic cacti.

Many cacti require a cold treatment during the winter to get them to flower.

Several species of Prickly Pears can be grown out-of-doors in Wisconsin. The Eastern Prickly Pear (Opuntia humifusa), Plains Prickly Pear (Opuntia macrorhiza), and Little Prickly Pear (Opuntia fragilis) all occur naturally in Wisconsin and do will when planted in gravelly, well drained soil in a sunny location. Areas under overhangs on the south side of buildings suit them well. In the autumn, plants lose water, become wrinkled, and collapse on the ground. Plants become turgid again in the spring when the soil warms. In late spring and summer, Prickly Pears produce large, showy yellow flowers.

The Little Prickly Pear is rare in Wisconsin, but common in other parts of its range. However, other cacti are rare throughout their ranges. Many of these are endangered because they are of very limited distribution or because they are of interest to collectors for private or commercial interest and have been over- collected. These cacti are listed int he Federal Register put out by the U.S. Fish and Wildlife Service and are protected by Federal Law. These plants should never be taken from the wild. For the average grower, there are more than enough kinds of cacti available commercially.

Next time you think of deserts and cacti, remember cacti are much more than plants with stickers!