The Saguaro Cactus (Carnegiea gigantea) is an Arizona icon. They are the largest cacti in the United States and are native only to the Sonoran Desert in southern Arizona and Sonoran Mexico. Although they can grow very tall, they have mostly very shallow roots. When the desert receives a good rainfall, the Saguaro absorbs as much water as possible, and the pleated sides expand to hold the moisture. The cactus is supported by woody ribs, corresponding to the pleats visible outside. The pleats are covered with long spines to protect the waxy soft skin from predators like ground squirrels and rabbits. Desert birds often make their nests inside the Saguaro, depending on the cactus’ natural ability to heal such a wound, leaving a cavity inside the cactus to be reused year after year.
How old is that Saguaro? Here is the official story from the Desert Botanical Garden in Phoenix: “on average and under the natural conditions existing just west of Tucson with 10 inches of rainfall annually, a saguaro often weighs less than an aspirin at age five and it may take about 10 years to get just an inch and a half tall, about the size of your thumb! Under these natural conditions it may take 20 years to almost attain one foot in height and 30 years to reach two feet tall, but by age 40 it may be up to four feet tall, by age 50 up to seven feet tall, by 75 up to 16 feet, and by age 100 almost 25 feet tall. Throughout its range and depending upon soil and rainfall, it first blooms between 40 and 75 (average 55) years old, usually starts to grow arms when it is between 50 to 100 years of age (average 70), and it may live for perhaps 200 years or more (again, no one knows for sure)”
According to that, this little one is probably 20 years old.
Known as the Tree of Life to the Pima Indians, the Mesquite (mess-KEET) is common in the deserts of Arizona. There are three native species in Arizona, the Honey Mesquite, the Velvet Mesquite and the Screwbean Mesquite. Mesquites can grow into large, shady trees and are used in landscaping as well as found growing wild.
Mesquites are members of the Fabaceae Family, one of the largest plant families. A familiar member of this family is the pea plant. The unifying characteristic of these plants is the seed pod they create, called a legume. Many legumes are able to convert atmospheric nitrogen into compounds useful to plants, through the nodules they have on their roots. Mesquites are able to do this and this makes them valuable to the other plants in the poor growing conditions of a desert. They also act as nurse trees for slow-growing plants. Birds, insects and other animals rely on the Mesquite beans as a food source and for shade and nesting. Often the Mesquites found throughout the desert are no more than a shrub, but under good conditions, they become large trees. Mesquites bloom in the Spring with creamy yellow dense, narrow clusters.
Historic records show that every part of the Mesquite had a use to the native peoples, for wood, for flour made of ground pods (pinole), the bark for baskets, medicines, and fabric. Today they are used in much the same ways. Mesquite burns slowly and is nearly smokeless, so it is popular as fuelwood. It makes an aromatic charcoal for barbecuing. Mesquite honey is very popular.
The Velvet Mesquite, Prosopis velutina, is very common in the southern part of Arizona. It is remarkable in appearance because of fuzzy, short hairs that cover the entire tree and pods, making it look velvety. The pods when ripe are narrow and brown and up to 8 inches long. This tree can grow a very long taproot, allowing it to access water deep underground. The Velvet Mesquite can get quite large, with a two-foot trunk and 30 feet tall or more. They can be found along streams or washes in shady thickets. Along some desert rivers, like the Verde and the San Pedro, dense mesquite bosques (forest in Spanish) can be found.
The Honey Mesquite, Prosopis glandulosa, has large spikes or thorns of up to three and a half inches and a sweet taste that make its beans delicious. The bean pods are mostly straight and up to 8 inches long. Its flower is a favorite of bees. It is a smaller tree than the Velvet Mesquite.
The Screwbean Mesquite, Prosopis pubesens, like the Velvet Mesquite, has rough bark that separates into long, narrow strips. The bean pod on this tree gives it the name, Screwbean, because instead of a long straight pod, the pod is tightly coiled and spirals to 2 inches.Tweets by @fanofnmtn
Two plants found in Arizona that are similar in appearance are (links) Lupine and Locoweed. There are several species of each plant. They are both members of the Fabaceae, or Pea Family. They have another similarity: they are both very toxic.
Cattle, sheep, horses and goats all have died from the effects of eating these plants.
Locoweed poisoning is the most widespread poisonous plant problem. Look closely at the leaves of Locoweed. They grow in clumps close to the ground and each leaf has 19-29 leaflets attached in pairs. They are covered with soft, fine hairs. There are 300 species of locoweed. Pictured is only a single species, native to northern Arizona. Locoweed contains toxic levels of swainsonine, a poisonous alkaloid. There has been extensive loss of range animals caused by eating locoweed. Horses in particular seek out Locoweed and become addicted. Signs of poisoning may not immediately appear, even for months. Then horses quickly die from damage to brain, digestive organs, or congestive heart failure.
Examine the leaves of the Lupine. Each leaf is palmately compound. It looks like your palm with fingers splayed. There are 5-7 leaflets to each leaf. Lupine is also toxic. The seeds and pods are the most toxic parts. Poisoning with Lupine can cause nervousness, foaming at the mouth, depression, reluctance to move about, birth defects, difficulty in breathing, twitching leg muscles, loss of all muscular control, convulsions, coma and death.
The flowers on both plants are remarkably similar, since they are all in the Pea Family. They are a beautiful blue addition to the flora, but be cautious about handling them, and don’t you or your animals eat them.