Shrubs Of The Great Basin: A Natural History

Saltsage

Saltsage Atriplex tridentata SALTSAGE IS A member of a complex of several related species of small stature found in heavy, alkaline, clay soils of valley flats in the eastern Great Basin. It is particularly abundant in the Lake Bonneville Basin in Utah. This entire complex, unlike the shadscale, four,winged, and Torrey salt, bushes, is only partly woody or subshrubby. Some individuals, in fact, ap, pear to be wholly herbaceous and die back to the woody rootstock each winter. Saltsage may get to be a meter tall, though it is generally much less. Most of the branches grow upright from the root crown and bear pale gray' green, narrow to oblong leaves between I and 5 centimeters in length. The sexes are mostly on separate plants. The female flowers, clustered at the ends of the branches, have two united bracts surrounding the pistil. In the mature fruits, these bracts have three or more prominent teeth at the apex and are smooth or, more frequently, possess bumps or tubercles on the sur, face. The yellow or brown male flowers are also borne in clusters at the ends of the branches. Howard C. Stutz of Brigham Young University and his colleagues, C. Lo, renzo Pope and Stewart C. Sanderson, have carried out extensive evolution, ary studies on saltsage and its close relatives. They found that every popula, tion of this species studied is distinctive and unique. One population in Tooele County, Utah, is unusually tall (growing 90 centimeters in one sea' son), is somewhat woody, and has large fruits and leaves, while another population near Delle, Utah, is nearly prostrate and has slender branches as well as small leaves and fruits. Interestingly enough, most saltsage populations are quite uniform within. Stutz attributes this to two factors: the strong root,sprouting tendency of saltsage, which makes for a lot of vegetative reproduction within each Saltsage SALTSAGE 65 colony, and a genetic attribute associated with species that have more than the usual two sets of chromosomes, the so~called polyploids. In our discus~ sion on the four~winged saltbush we point out that all populations studied, except one, were found to be tetraploid; that is, they had four sets of chro~ mosomes. In the case ofsaltsage, Stutz found that most populations are hexa~ ploid-they have six sets of chromosomes for a total of fifty~four. Stutz speculates that the enormous variability between individual populations of saltsage is a consequence of the unexploited habitats exposed in the Great Basin by the recent disappearance of the Ice Age lakes, Bonneville and Lahontan. The desert "islands" separated by parallel mountain ranges have effectively isolated each population, and in such instances, in small colo~ nies, evolution tends to be accelerated as chance variations spread rapidly through the population. Natural hybrids between saltsage and four~winged saltbush were found by Stutz at a number of sites. These individuals had five sets of chromosomes for a total of forty~five. These hybrids in nature provide, in subsequent gen~ erations, a bridge by means of which some genes could be transferred be~ tween these two species. This process results in adaptive combinations which may eventually become new species. One of these new combinations is a low~growing form in the Reese River Valley, Nevada; another is a robust form near Knolls, Tooele County, Utah; and one is an upright, bushy type near Grantsville, Tooele County, Utah. All of this evidence makes apparent the truth of Stutz' observation that the saltbushes are in a period of ex~ plosive evolution. If so much has happened in a period of a few thousand years or less, one wonders what the saltbushes and their allies will be like in another few hundreds or thousands of years. If humans are still around then, it is comforting to realize that botanists will still have plenty of things to study, what with these new forms constantly being spewed out by the forces of evolution. Sometimes saltsage grows in nearly pure stands, and it appears to be able to withstand very high concentrations of salt in the soil. Similar to saltsage but less able to withstand an extremely saline environment is the sickle salt~ sage, A. falcata, which can be distinguished by the single, frequently curved, long, pointed tooth at the top of each fruiting bract. Sickle saltsage is not really a shrub, however, since it is woody only at the ground level. Craig A. Hanson...