Fourwing Saltbush (Atriplex canescens) Seed Transfer Zones

摘要

Atriplex canescens (Pursh.) Nutt. is the most widespread species of perennial Atriplex in North America. Throughout its distributional range, A. canescens shows considerable between-population variation. Some of this variation may be due to phenotypic plasticity but most of it appears to be genetic. Mutations, polyploidy, introgressive hybridization, and segregation from interspecific hybrids all appear to have contributed to its extensive heritable variation. Polyploidy is unusually common with numerous chromosome races (2x, 4x, 6x, 8x, 10x, 12x, 14x, 20x). Fourwing saltbush is widely used for reclamation plantings. Proper identification is important to the utilization of fourwing saltbush in such plantings. While many of the races have been formally named as varieties, others have not. Even though differentiated by ploidy, chemical constituents, geographic distribution, and statistical distribution of morphological characters, races may lack sufficient diagnostic characters to allow facile identification, at least in the herbarium. Rather than combining unnamed races under those that do have a taxonomic name, it seems better at present not to use the formal infraspecific categories in treating the fourwing saltbushes, but to consider them all as races. Seed transfer should be within the geographical distribution limits of each race. The most common race, by far, is Occidentalis. We recommend four overlapping seed transfer zones for race Occidentalis in the United States: (1) Northern Intermountain, (2) Western Great Plains, (3) Colorado Plateau/Great Basin/Columbia Basin, and (4) Southwestern. Source seed populations from near the planting sites generally do well; and populations generally perform better when moved south and/or to lower elevations than when moved north and/or up in elevation.