Region III Quarterly

Volume 2 - No. 3

July, 1940


By Dr. W. B. McDougall,
Regional Biologist.

It has been said that a visit to the desert invariably brings a desire to return. There is a peculiar, unique sort of charm that grips you, especially after you have slept out under the stars among the cacti, ocotillo, and palo verde trees. A love of the desert seems to grow within you and become more intense each time you return.

There are various kinds of desert, such as the sagebrush desert and the creosote bush desert and the spurge desert of Africa, but in certain respects the cactus desert, which reaches its noblest development from southern Arizona southward through Mexico and Central America, is the most unique and the most charming of all. With the exception of a single genus, the members of which grow as epiphytes on other plants in Africa, the cacti are strictly American plants. Every national park and monument in Region III boasts of certain species of cacti, but if you wish to see the most wonderful natural displays of cacti in the United States, go to Saguaro National Monument, east of Tucson; and the Organ Pipe Cactus National Monument, south of Ajo, in Arizona. If you ask the custodian of either of these monuments how many kinds of cacti there are in his monument, he will give you a number that will surprise you, but he will admit that he does not know the exact number because the areas have not been explored thoroughly enough to determine the numbers.

In North and South America together there are now known to be more than 1,200 different species of cacti. They vary in size from the little fishhook cactus that is seldom mere than 2 inches high, to the giant cactus, or saguaro, that sometimes reaches nearly 50 feet in height. There are certain characteristics, however, that are common to all cacti. They all have very fleshy stems in which they can store great quantities of water to tide them over periods of drought. The stems are always green, too, so that they can manufacture starches and sugars from water and the carbon dioxide of the atmosphere, just as green leaves do. This is important because most cacti do not have any leaves; those that do have a few small leaves usually lose all of them very soon after the end of a rainy season.

The flowers of most cacti are very showy. The sepals, petals, and stamens are numerous, but there is only one pistil. The ovary is below all of the other parts of the flower so that the other parts appear to be growing from the top of the ovary. After the other parts of the flower have withered and dropped away, the ovary develops into a large edible berry which in many cases is sweet.

The cacti have no very close relatives. Plant families that are closely related are grouped together into plant orders, but in the order in which the cactus family is placed there are no other families. Probably the nearest relatives of the cacti are such plants as the evening primroses, the myrtles, the begonias, and the pumpkins and melons. It is believed that during the evolution of the plant kingdom the cacti and all of these other plants that I have mentioned as being related to the cacti were developed from roses or rose-like plants.

Quite often plants that are totally unrelated to the cacti are mistaken for cacti. I remember being on a train going west when a salesman came through the car offering for sale some beautiful handmade handkerchiefs which he said were made from certain cacti of the desert. He promised that a few miles farther along he would be able to point out the species of cacti from which the handkerchiefs were made. He did point out some beautiful desert plants but they were the ocotillo, or desert flame, which are not cacti and are not even closely related to cacti. At another time, in northern Arizona, I saw a young man pointing out certain plants and overheard him telling a friend from a foreign country that they were the plants from which cactus candy is made. The plants were yuccas which are related to lilies and not to cacti. The joshua tree is another plant that is sometimes mistaken for a cactus. It is fully as unique as the cacti but it is a yucca and not a cactus.

The largest of all the cacti is the saguaro, or giant cactus, (Carnegia gigantia) the largest specimens of which are nearly 50 feet tall and nearly 250 years old. The genus name, Carnegia, was given to the plant in honor of Andrew Carnegie, through whose philanthropy the Desert Laboratory of the Carnegie Institution of Washington was established near Tucson, Arizona, early in the present century, specifically for the study of desert plant life. The saguaro grows very slowly. At 10 years of age it may be from 4 to 6 inches tall. In 30 years it may have reached a height of 3 feet. At 50 to 60 years of age, and with a height of 15 to 20 feet, it may be ready to produce its first flowers and it may then produce a crop of flowers and fruits annually for 200 years. Usually several branches are produced about 8 to 12 feet above the ground. Normally these branches, or arms, grow outward nearly at right angles to the main stem and then curve upward to a vertical position, giving the plant the appearance of a huge candelabra. Often, however, these arms assume most grotesque positions. One saguaro may have an arm uplifted as though greeting you with a respectful salute, while another may cause you to wonder if it is not laughing at you and trying to hide its derision behind an uplifted arm.

The structure of the stem of the saguaro is rather remarkable. There is a cylindrical core consisting of 12 to 24 rods which are technically called fibrovascular bundles. Each of these bundles or rods is composed partly of strengthening tissue and partly of conducting tissue for the vertical conduction or transportation of sap. Both inside and outside of this cylindrical core of rods is the succulent, water-holding tissue which makes up the bulk of the stem. The rods, which vary in diameter from 1 to 2 inches, make the stem strong enough to resist the violent winds that often sweep across the desert during the short rainy seasons. These rods are used by Papago Indians for fuel and for building materials. The outer surface of the stem is fluted like an accordian, with furrows 1 to 2 inches deep, depending upon the amount of water in the stem. The stem is thus able to expand its diameter during a rainy season as it fills up with water, and then to contract slowly as it uses up the stored water during a prolonged dry season. Because of its remarkable water storage capacity the plant is able to produce flowers and fruits even if an entire year passes without a drop of rain.

blooming saguaro

The saguaros usually begin blooming in May and continue for a month or so. The fruits ripen in June and July. The flowers are white and 2 or 3 inches across. They bloom only in the night but remain open until sometime during the following forenoon so it is not necessary to stay up all night in order to see them. The flowers are visited for nectar and pollen by both night-flying and day-flying insects which, incidentally, aid the plant in transferring pollen from stamens to stigmas which is necessary before seeds can be produced. The fruits are pear-shaped, about 3 inches long, greenish-purple on the outside and crimson within. These fruits are edible and are as important to the Papago Indian as are pinon nuts to the Navaho.

The saguaro, like practically all cacti, is covered everywhere with spines. These spines contain a considerable amount of resin. If you take one from the plant and touch a match to its end it will burn like a candle. The spines afford considerable protection against certain animals. One of the best and most dense forests of saguaros is found in Saguaro National Monument.

The organ pipe cactus (Lemaireocereus thurberi) is, in many respects, as unique and interesting as the saguaro. Its distribution in the United States is much more restricted than is that of the saguaro. It is believed that more than 90 per cent of all organ pipe cacti in the United States are within the boundaries of the Organ Pipe Cactus National Monument, south of Ajo, Arizona, but the species also extends south into Mexico. It is a large plant but not so large as the saguaro. It branches from the base, usually producing from 5 to 15 upright sterns which curve inward at the base and grow from 10 to 15 feet high. The general structure of the stems is similar to that of the saguaro. The large white flowers are produced at about the same time as those of the saguaro. The fruits are gathered by the Papago Indians and mixed with those of the saguaro in order to produce a slightly different flavor to the jam made from them.

The night-blooming cereus (Paniocereus gregii), sometimes called sweet potato cactus because of its large tuberous root, produces flowers that are among the most beautiful and fragrant of all known flowers. The species is found from southwestern Texas to Arizona and south into Mexico. There are probably many more of these plants within a 100-mile radius about Tucson, Arizona, than in all the rest of the United States together. The stems are 4 or 5-angled and rather slender. The plants are often found growing at the base of the palo verde tree where the weak stems can lean against the tree for support, if necessary.

The night-blooming cereus blooms in June. The blooming date is looked forward to with a great deal of interest each year at Casa Grande National Monument, Arizona. Sometimes more than 90 per cent of the flowers in a given locality bloom on the same night and for that one night the atmosphere is filled with the delicious, spicy fragrance of these exquisite, white blossoms. They open at sundown and one can actually watch the process, for the major part of it takes place within an hour, although it may be two hours more before the flower is fully expanded. When fully open, the flowers are 6 to 8 inches long, including the ovary and tube, and 3 inches or more across. The next morning, shortly after sunrise, the flowers close up almost as rapidly as they opened. The scarlet, fleshy fruits are 1 to 1-1/2 inches long and about 1 inch in diameter. They ripen in September or October and are edible.

I am sometimes asked why Nature spends an entire year in getting ready to produce such perfectly beautiful and fragrant flowers and then causes them to bloom during the night and way out in the desert where they may "blush unseen and waste their fragrance on the desert air." As a matter of fact, the flowers of the night-blooming cereus never blush unseen and their fragrance is never wasted. It must be remembered that Nature does not produce flowers to please the eye of man. She produces them to please the eye of insect. It is our good fortune that the flowers are pleasing to us, but it is the insects that need to be attracted to the flowers because it is the insects that bring about the transfer of pollen from one flower to another which is so necessary in the orderly process of reproduction; and reproduction is the greatest event in the life of a plant, just as it is in the life of an animal. Thousands of moths and other night flying insects are actively at work while these flowers are in bloom, and they both see and smell the flowers.

Organ pipe cactus

One of the largest and most widely distributed of the groups of cacti is the genus Opuntia. This is the genus to which the prickly pears and chollas and related forms belong. All members of the genus have jointed stems, but in the prickly pears the joints are flat, while in the chollas they are cylindrical. Like most cacti, the Opuntias all produce beautiful flowers, some of them yellow and some of them rose or pink, and many of them produce edible fruits. Some of the prickly pears grew upright and may become 6 feet or more in height. Others spread over the ground, take root from those joints that come in contact with the soil, and form an extensive mat. Such plants aid in protecting the soil from surface erosion.

The jumping cactus (Opuntia fulgida) is the spiniest and most aggressive of the larger cacti. The joints do not actually jump at you but they seprate from the plant very easily and if you accidentally touch the plant you are likely to regret it. I well remember one personal experience when I was standing near one of these plants in Organ Pipe Cactus National Monument, talking with a couple of friends. As I talked, I motioned with my hands, as a Scotchman will, and suddenly I found a cholla joint clinging to the back of my right hand. I used a stick to pry the cholla from my hand, painfully, but it left behind about a hundred spines sticking into my flesh. They had to be pulled out one by one and, since each spine has a barb at the end, it was just like pulling a hundred little fish hooks from the back of my hand. The joints of the cholla serve as a means of reproduction. Each one, under favorable conditions, will take root and grow into a new plant. More new plants are produced by this means than from seed.

The barrel cactus (Ferocactus), of which there are several species, has saved many a man from death by thirst, in olden days when travel was slow. The barrel cactus produces a single upright stem and may become several feet high and a foot or more in diameter. If the stem is broken open and the pulp crushed, a considerable amount of juice is obtained. This juice is not particularly palatable. It reminds one somewhat of the taste of a raw cucumber. But when one is sufficiently thirsty, he does not quibble over the flavor of the only liquid available.

I have described only a few of the numerous kinds of cacti to be found in our southwestern national parks and monuments. There are the rainbow cactus, which produces such beautiful pink flowers with white centers; and the strawberry cactus, whose fruits are so highly prized, and many others. But lack of space prohibits further discussion at this time. And, anyway, the only way to acquire a full appreciation of this unique and charming family of plants is to go and see its members in their natural homes. It cannot be obtained by reading about them.

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Date: 17-Nov-2005