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Pholisma sonorae is an obscure, parasitic plant with strange attributes. The plants are gray and mushroom-shaped, and height depends on the degree to which blowing sand covers the scaly stem. This succulent stem extends 1-2 m below the sand, and is attached to roots of nearby host plants. The scales on the stem are actually modified leaves. Pholisma appears to be perennial (G. Yatskievich, 1985), dying back to undifferentiated tissue at the infection site on the host plant every year. Incredibly, host plants do not appear to be depleted by Pholisma infestation, and Pholisma plants have been unearthed and weighed, with the weights exceeding those of host plants. Some of the host plant species include Tiquilia plicata, Psorothamnus emoryi, Ambrosia dumosa, and Pluchea sericea. There has been speculation as to whether Pholisma absorbs water independently from host plants, but this has been discounted as Pholisma has no root hairs. Instead, water is probably absorbed through the many stomata on the scale-like leaves (Yatskievich, 1985). This water taken directly from the sand can then move into the host plant during times of drought stress. Thus, the relationship between Pholisma and the host plant is not parasitic in the strictest sense. The inflorescences form the 'cap' of the mushroom-like plant, bearing numerous purple flowers arranged in a ring toward the outer edge of the cap. Each flower is surrounded by a hairy calyx, and the massed together calyces give the inflorescence a gray-white fuzzy appearance, while protecting plants from sun and heat. Fruits are capsules having 12-20 tiny seeds, similar in size to the surrounding grains of sand.
Stems of plants were eaten raw or roasted by native American tribes (Sand Papagos and Cocopas). The flavor of the stems is slightly sweet, with the texture of a crisp radish. Peter Brady, a member of a party surveying the sand dune area for a suitable railroad route, wrote of the Native Americans of the Adair Bay region that most had teeth decayed or eroded to the gum level. The low level of dental health in the Papago has been associated with the diet containing high proportions of sand food. Consumption of Pholisma by humans has been discontinued as a result of lifestyle changes and relocation of Native Americans who lived near the dunes.
An additional species, Pholisma arenaria, can be found nearby, on dunes having a slightly different mineral composition., and color. While P. sonorae occurs on shifting white sands, P. arenaria can be found on more stabilized (higher vegetation density) dunes of pinkish sand. Inflorescences of P. arenaria are markedly different than P. sonorae, having a narrower cone-shaped 'cap', and calyces with less hair.
Plants are not federally listed, but are considered very rare on the global scale (G1), and are protected by both Arizona and California. Current threats to Pholisma include development (conversion of dune habitat to housing and agricultural land), and off-road vehicle use. The Imperial and Algodones dunes are located primarily on BLM lands, and although a small section of habitat has been set aside in California, restricting off-road vehicle use, the majority of the land is open to the public. The nature of the off-road vehicle problem is two-fold, with both host plants destroyed and Pholisma growing close to recreational sites being destroyed. Garden staff visits such sites annually to get an idea of the degree of damage. At one exit just off the highway where Pholisma were relatively frequent three years ago, few plants could be found, and the area was denuded of host plants also. Fragments of stems of Tiquilia and Eriogonum lay on the sand, broken by those driving on them. In Arizona, plants are extremely rare, almost to the point of extirpation, due to expansion of the city of Yuma, and conversion to agriculture. The sand dune habitat is extremely limited within the boundaries of the state of Arizona. A site documented by a herbarium specimen on U.S.-Mex. Hill was visited during 1998, and no plants were located. As the site is rather remote and undeveloped, it appears that dune stabilization by associated species has sufficiently altered the habitat to the extent that Pholisma sonorae cannot grow there. Two years ago, Pholisma was located near a lemon grove, at a site documented by a herbarium specimen made by Jepson. South of the U.S.-Mexican border, far more sand dune habitat can be found, but the status of the plants is unknown for that area.
Desert Botanical Garden is currently processing seeds by hand. Collected seeds from the 1998 lot have been hand-cleaned by volunteers and counted using an analytical balance. A small mass containing hundreds of seeds were sent to Dr. Valerie Pence at Cincinnati Zoo and Botanical Garden. Seeds had been sent previously in 1987, but they had been previously frozen for an undetermined amount of time. Dr. Pence conducted tetrazolium tests on the 1987 seeds and determined that they were non-viable. Information from G. Yatskievich (pers. com., 1993) about the nature of the undifferentiated embryo, and oily endosperm led Dr. Pence to believe that freezing may have permanently damaged the seeds. Germination experiments at the Garden using rootbound host plants were also conducted on Pholisma in 1993, but no seed germinated. A dissertation on Ammobroma (Pholisma) sonorae germination requirements concluded that all known and experimental methods used to germinate seed of any plant were attempted, and no germination occurred. Seeds were recollected in 2000, and are still being cleaned.
Yatskievich, G., Cactus and Succulent Journal (U.S.), vol. 57, 1985.
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