Life on the Dunes - Part 2
by Wayne P. Armstrong
Many animals and plants have adapted to life in a sea of drifting sand. During years with favorable winter rains carpets of pink sand verbena (Abronia villosa), white dune evening-primrose (Oenothera deltoides) and yellow sunflower (Geraea canescens) may extend for miles, and the air is filled with the sweet aroma of fragrant blossoms. Deep-rooted shrubs, such as mesquite (Prosopis glandulosa), creosote bush (Larrea tridentata) and desert buckwheat (Eriogonum deserticola) provide vital shade and food for a host of animals, from insects and reptiles to birds and mammals. Often entire rodent condominiums are constructed beneath the protective cover of dune shrubs.
Dune Lizards & Snakes
Two remarkable dune residents, the fringe-toed lizard (Uma notata) and shovel-nosed sand snake (Chionactis occipitalis), are well adapted for rapid burrowing through sand, a phenomenon known as "sand swimming." At depths of only 12 inches (30 cm), the temperature may be 50 Fahrenheit degrees cooler. Fringe-toed lizards are often seen scurrying over sand dunes during mild spring days and even in the hot summer. Their toes are fringed with elongate, pointed scales which provide traction in the sand (like extra-grip tread). They can run with amazing speed across steep dunes and then stop suddenly and wriggle out of sight into the cooler layers of sand. Their special eyelids and countersunk lower jaw keeps out sand grains.
The shovel-nosed sand snake and banded sand snake (Chilomeniscus cinctus) are also well-adapted for burrowing through sand with their streamlined heads and smooth scalation which minimize friction. The way they glide swiftly through the sand is reminiscent of the giant "sand worms" in the sci-fi movie "Dune," and the terrifying sand creatures in the movie "Tremors." Although they are harmless, colorful banded sand snakes are sometimes mistaken for poisonous coral snakes; however, coral snakes have a black-tipped head and red bands that completely encircle their bodies, bordered by yellow or white bands.
Sand Food & Sand Plant
One of the most interesting of all dune plants, and certainly one of the most bizarre wildflowers in North America is "sand food" (Pholisma sonorae), formerly placed in the genus Ammobroma. This amazing parasitic flowering plant grows in the Algodones Dunes of southeastern California and adjacent Arizona, and in the sand dunes of El Gran Desierto in Sonora, Mexico (north of Bahia Adair in the Gulf of California). The southernmost extent appears to be the region around Bahia Adair on the Sea of Cortez coast of Sonora, Mexico. Within this area, the plants grow on sand dunes produced by wind transport of sand from the beaches of ancient Lake Cahuilla and the Colorado River delta.
Another unusual species of sand food (Pholisma culiacana) is endemic to rocky, subtropical thorn scrub 500 miles (800 km) south in Sinaloa, Mexico. According to Gary Nabhan (Desert Plants Vol. 2, 1980), the disjunct distribution of these two species may be explained by plate tectonics. Floras west of the San Andreas fault and Gulf rift, in southern California and Baja California, have been displaced northward at least 500 km since the Miocene epoch (about 30 million years ago). Assuming that P. culiacana is more like the tropical progenitor of both species, P. sonorae could have diverged into a more xeric (drought resistant) species west of the San Andreas fault as peninsular California moved northward. Present day populations of P. sonorae east of the fault could have migrated there by shifting sand dunes in the region.
Sand food is a root parasite with a thick, scaly stem that may extend 6 feet (2 m) or more into the dune where it attaches to the roots of nearby shrubs deep in the soft sand. The entire plant lives below the surface of the sand, with only the flower head pushing above sand during early spring. The scaly stem is without chlorophyll and is nonphotosynthetic, and all of its vital organic nutrients (amino acids and carbohydrates) come from nearby host shrubs. An old, dried flower head with a long, subterranean scaly stem superficially resembles a sand dollar attached to a long piece of seaweed.
One of sand food's common host shrubs on the Algodones Dunes is dune buckwheat (Eriogonum deserticola). [The related P. culiacana has completely different host shrubs in the thorn scrub of Sinaloa, Mexico.] This endemic buckwheat is a large shrub with picturesque, twisted trunks and long, deep roots that are often exposed by shifting sand. Sand food also parasitizes the roots of two mat-like dune shrubs in the borage family, Coldenia plicata and C. palmeri. Other host shrubs include dyeweed (Psorothamnus emoryi), bur-sage (Ambrosia dumosa) and arrowweed (Pluchea sericea). The latter shrub is more typical of marsh areas, and in the early 1930s, Franklin A. Thackery discovered 106 sand food plants arising from a single arrowweed plant near an irrigation canal in Imperial County, California (north of Calipatria).
The host plant weighed just over one pound, while the 106 sand food plants weighed 46 pounds. In this remarkable case, the parasite outweighed its host by more than 3600 percent! Of course, most of the sand food's combined weight was water stored in its fleshy tissues. Thackery concluded that the parasite was not overtaxing its host, and was absorbing water on its own to supplement that which was provided by the host. Because sand food is so brittle, Thackery had to suspend each of the 106 stems with separate strings in order to take his photograph. His remarkable photograph in Desert Magazine (Vol. 16, 1953) looks like a sand food puppet show!
As in all flowering plants, flowers and seed-bearing fruits provide the vital genetic link between successive generations. The flower heads (inflorescences) of sand food develop on the surface of the sand where they can be visited by pollinators, and resemble fuzzy mushrooms or gray powder puffs bearing numerous tiny lavender flowers. Individual flowers are surrounded by a hairy calyx, and the masses of hairy calyces give the heads a sand-colored, woolly texture and appearance which undoubtedly reflects light and heat on the sun-baked dunes. The heads may reach 5 inches (12 cm) in diameter and the flowers often appear in a circular pattern.
Sand food flowers are apparently insect-pollinated, and according to R.L. Dressler and Job Kuijt (Madrono Vol. 19, 1968), the flowers of A. culiacana have a faint, sweet odor and are visited by flies, beetles and small butterflies. Sand food plants on the Algodones Dunes are sometimes infested with small ants and mealybugs. The ants may be after the small seeds, or perhaps the sweet nectar secretion from the mealybugs known as "honeydew." Following pollination, each flower gives rise to a small dry fruit (capsule) composed of 12 to 20 minute seeds arranged in a circle like wedges of cheese. Depending on favorable winter rains and pollination, each flower head may produce hundreds of seeds.
The scaly stems extend more than 6 feet (2 m) into the sand where they are attached to the roots of dune buckwheat, or another host shrub. It is difficult to trace the origin of these strange plants because the sand caves in as fast as you can shovel it out. Native Indians, including the Sand Papagos and Cocopas, ate the fleshy stems of sand food, either raw or roasted over a campfire. The stems were also dried in the sun and ground on a metate with mesquite beans, forming a flour called "pinole."
The flavor of raw stems is pleasantly sweet, with a texture similar to a crisp, juicy radish; however, this is a rare desert plant and should not be harvested by hungry nature lovers. According to the authority of desert plants, Dr. Edmund C. Jaeger, when roasted the stems resemble the flavor of well-browned yams (red sweet potatoes). The closely-related root parasite, called sand plant or pholisma (Pholisma arenarium), has a fleshy, scaly, subterranean stem and growth habit similar to sand food. It produces a peculiar egg-shaped cluster of lavender flowers in sandy areas of the Colorado Desert and coastal sand dunes in California. Unlike sand food, its raw stems are not particularly flavorful or palatable--at least in this author's opinion.
How the seedlings of these unusual root parasites are able to find the host root buried deep in the sand is truly remarkable. It is discussed by Job Kuijt in The Biology of Parasitic Flowering Plants, 1969. According to Dr. Kuijt, the sand plant (Pholisma arenarium) sends out "pilot roots" two feet (0.6 m) below the surface of the sand. When they reach the vicinity of a host shrub, the pilot roots send out special "haustorial roots" which connect and penetrate the host root.
The haustorial connection (haustorium) absorbs carbohydrates and amino acids manufactured by the photosynthetic host shrub. Other factors may also be involved in finding the host roots. The small seeds may move downward through the sand or may be buried by continually shifting sand dunes which are subsequently colonized by new host vegetation. They may also be carried deep into the sand by harvester ants and by rodents (kangaroo rats) that burrow into the dunes under host shrubs.
Antlions & the Infamous Sand Wasp
Any discussion of denizens of drifting sand would be incomplete without mentioning two very unusual insects, the antlion and the sand wasp. The antlion resembles a grotesque small scale version of the sand creature in the Star Trek II film, "The Wrath of Khan." It builds a circular crater in the sand and then waits patiently under the sand at the bottom of the pit for a hapless passerby. The steep crater walls make escape by small crawling insects virtually impossible. Struggling victims are literally pulled into the sand and sucked dry by the hollow fangs (jaws) of the antlion. If antlions were 6 feet (2 m) long, they would be a formidable desert sci-fi monster that could easily grab humans!
Sand wasps (Bembix species) dig tunnels in soft sand where they live in elaborate "condominiums." They are readily distinguished from other wasp species by their elongate, triangular labrum (lip). Sand wasps differ from spider wasps, mud daubers and many other digging wasps that provide their larvae with a single cache of food that must last throughout the larva's development. Sand wasps continually catch insects, such as flies, and bring them home to their burrows. They are often seen hovering over dunes in search of small insects to feed their young. Although they are not social insects like hornets, yellow jackets and honey bees, they do nest in the same vicinity, and tend to develop a primitive type of colony.
A well-camouflaged desert iguana (Dipsosaurus dorsalis) peering out of its burrow in the sand. Tolerant of high temperatures, this lizard can be seen scurrying across sand hummocks and roads on hot, sunny days when most other lizards seek shelter.
Sand Dune Preservation
Many people ask why sand dunes should be preserved; "they are just piles of sand devoid of plants and animals." Nothing could be further from the truth. There are hundreds of dune species throughout the southwestern United States and Mexico, some of which are considered rare and endangered by the United States Fish and Wildlife Service. This is because their limited and specialized habitats are threatened by urbanization and various motorized off-road vehicles.
In addition, some sand dunes have unique habitats that occur in no other dune chains. For this reason, the Bureau of Land Management has closed a section of the Glamis dunes north of Highway 78 in Imperial County, California to all motorized vehicles. This area has been designated a National Natural Landmark, and only represents a small part of the enormous Algodones Dunes, most of which are still open to off-road vehicles. At least one section of this magnificent chain of sand dunes will remain in its pristine form for educational activities and field research; for photographers, naturalists, scientists and anyone who enjoys accessible, picturesque dunes.
To read part one Sand Dunes: Phenomena of the Wind #1
References About Sand Dune Inhabitants
1. Armstrong, W.P. 1980. "Sand Food: A Strange Plant of the Algodones Dunes." Fremontia 7: 3-9.
2. Armstrong, W.P. 1980. "More About Sand Food." Fremontia 8: 30-31.
3. Dressler, R.L. and J. Kuijt. 1968. "A Second Species of Ammobroma (Lennoaceae) in Sinaloa, Mexico." Madrono 19: 179-182.
4. Jaeger, E.C. 1941. Desert Wildflowers. Stanford University Press, Stanford.
5. Kuijt, Job. 1969. The Biology of Parasitic Flowering Plants. University of California Press, Berkeley.
6. Nabhan, G. 1980. "Ammobroma sonorae, An Endangered Parasitic Plant in Extremely Arid North America." Desert Plants 2: 188-196.
7. Stebbins, R.C. 1966. A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin Company, Boston.
8. Thackery, F.A. 1953. "Sand Food of the Papagos." Desert Magazine 16: 22-24.
Wayne P. Armstrong is Professor of Botany
Life Sciences Department - Palomar College - San Marcos, California.
He is publisher of WAYNE'S WORD®: A Newsletter of Natural History
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