Plants

An unusual tree that is not very commonly known to us is the desert ironwood. True to its name, the desert ironwood grows in the Sonoroan Desert, which is located in southwestern Arizona, southern California, and the northwestern part of Mexico. Even though the Sonoran Desert is mostly devoid of plant life, except for shrubs, the desert ironwood is able to grow.

They thrive on the rare sandy washes in the desert where water is available.
The leaves and flowers that grown from this tree are similar looking to that of the sweetpea, which is probably why this tree come from the peas family. They can grow to at least 30 feet into the air, but there are some that can grow very small. The growth rate of these trees is incredibly slow with wide spreading crowns and bluish gray-green leaves. They can live up to 1,500 years.

The Spanish name for these trees is palo fierro. Like most plants they serve an important purpose to the animals that survive in the desert by offering them food and shelter from the sun. They are seen as very important trees in the desert because they are able to provide a micro-habitat for the animal neighbors around them. Nitrogen-fixing nodules on the root system, and nutrient-rich leaf litter fertilizes the soil around it.

Native bees pollinate the ironwood flowers, which are also used as medicine. The ironwood is known as a “nurse plant”. It provides a safe place for seed germination, and protects seedlings from extreme cold. It also protects saplings from the damaging effects of the sun.
The bark on young branches is gray and smooth. Older bark becomes wrinkled and creased, eventually shredding on older trunks.

It has leathery, compound, pinnate leaves about 2 inches long with 6 to 9 leaflets about .75 inches long. The leaves are covered with fine hairs. A pair of thorns about .5 inch long grows at the base of each leaf. During the dry season the ironwoods will drop their leaves to conserve water. They never drop all of their leaves, so their canopy provides protection from frost and high heat all year round.

They bloom from April to June just before the new leaves grow back. Clusters of pea-like flowers ranging from pink, pale-rose, to white, grow in archs at the end of branches. These develop into brown, bean-like seedpods about 2 inches long. Each seedpod has 1 to 4 brown beans in it. The ironwood seeds mature at a time of year when very few plants are producing fruit. Wildlife is highly dependent on its seeds. The seeds can also be roasted and eaten, or ground into a flour.

When given enough water the desert ironwood is an evergreen tree. It is being used in landscape plantings as a shade tree. The desert ironwood is well adapted to the heat and lack of water of the Sonoran Desert however. The desert ironwood is drought deciduous, and will shed its leaves during dry periods to conserve water. This avoids loss of water through transpiration. The desert ironwood puts all of its energy towards flowering and regeneration after the spring rains.

New leaves appear shortly after the tree has begun to bloom. The leaves have a soft covering of hair which protects them from damaging ultraviolet rays of the sun. The leaf litter under the tree acts as mulch and keeps the soil around the tree moist for longer periods after a rain. Sharp thorns discourage browsing by desert inhabitants. The wood of the desert ironwood is very hard and dense.

It actually sinks in water. It was used by the Seri Native Americans of Mexico for tool handles. Today the Seri Indians make carvings of desert plants and animals from the ironwood. Dead wood is gathered from the desert floor, and the carvings are made with hand tools. Tradition has it that carvings made from the desert ironwood bring good fortune and long life. The carvings are in much demand, especially large carvings, and bring in a lot of money. Illegal harvesting of ironwood is on the rise and live trees are being cut down.

Desert ironwood burns very hot and is used to make charcoal. Woodcutting causes an average of 17% reduction in ironwood. Wood has been illegally cut even in the Organ Pipe Cactus National Monument and other protected areas.