GENETIC DIFFERENCES BETWEEN LARGE AND SMALL ARTEMISIA TRIDENTATA PLANTS IN CONTIGUOUS POPULATIONS

Genotypic and phenotypic variation are characteristic of A. tridentata Nutt. plants. One obvious expression is the variability of A. tridentata plant stature in response to soil water conditions. Large statured plants are usually associated with mesic habitats such as gullies or swales, while small statured plants occupy adjacent xeric habitats.; The primary purpose of this study was to investigate the genetic differences of large and small statured A. tridentata plants in contiguous populations. The study tested two hypotheses: (1) genetic differences do exist between the large and small statured plants in contiguous populations; and (2) significant intermixing between the contiguous large and small plant populations does not occur.; Three sites were selected to conduct the research. At each site, the large plants grew within and along a gully. Plant height decreased with distance away from the gully.; Soil-water potential, leaf-water potential and leaf-transpiration resistance were measured during the summer of 1980 to quantify the mesic and xeric habitats. Also, soil and plant tissue mineral analyses were conducted to determine if any additional edaphic differences existed between the two habitats.; Six separate experiments tested the hypotheses. Greenhouse and uniform garden studies compared seedling growth of the large and small plant populations. Morphological, phenological and cytological studies also examined genetic differences between the large and small plant populations. A chromatographic study tested whether the large and small plants intermixed between the contiguous populations.; The results of the plant-water relationship study and soil survey quantified the soil differences in water between the mesic and xeric habitats. Small plants experienced greater drought conditions than large plants during the summer of 1980. Soils associated with large plants were Torrifluvents. The soils associated with the small plants were a Camborthid Haplargid and Torrifluvent.; The results of the research support the hypothesis that large and small plants are genetically different. In addition, the data point out that the large plants were A. tridentata Nutt. ssp. tridentata, while the small plants were A. tridentata Nutt. ssp. wyomingensis Beetle and Young. In both the greenhouse and uniform garden studies, seedlings from ssp. tridentata plants grew taller than seedlings from ssp. wyomingensis plants. Morphological measurements of field plants revealed differences between ssp. tridentata and wyomingensis plants. The leaf-length/width ratio and leader length of ssp. tridentata plants were greater than for ssp. wyomingensis. However, there were no differences in leaf length, leaf width, seed weight, and percent seed germination between the two subspecies. Phenological development during 1980 was not the same for ssp. tridentata and wyomingensis plants. Flowering of ssp. wyomingensis plants occurred earlier than did flowering of ssp. tridentata plants. The cytogical study showed that ssp. tridentata plants were diploid (2N = 18) while ssp. wyomingensis plants were tetraploid (2N = 36).; The hypothesis that the large and small populations do not significantly intermix must be accepted. Subspecies tridentata plants appeared to be separated from ssp. wyomingensis plants based on the cluster analysis of their chromatograms. Using the dendrograms from each site as a guide, contingency-table analyses were performed to test for independence between subspecies and habitat position. The results of these analyses showed the ssp. tridentata plants occurred more frequently in the mesic habitat. On the other hand, ssp. wyomingensis plants occurred more frequently in the xeric habitat. The differences in polyploidy and competitive exclusion may explain the separation of the subspecies between the mesic and xeric habitats.