Plants are adapted to their local and regional environments. Recognizing this adaptive variation and the environmental causes are key to determine how seed or seedling can be moved on the landscape. Before these seed movement strategies can be implemented, it is also important to identify closely related taxa, since they also reflect adaptive divergence. Big sagebrush is a good example. Big sagebrush is composed of three subspecies that occupy different environments. These subspecies can co-occur in some areas, while in other areas they do not, depending on the heterogeneity of the environment. Moreover, subspecies can sometimes be difficult to visually differentiate in the field. These properties of big sagebrush make assessments of the subspecies composition of commercial seed collections challenging for both seed collectors and certifiers. Forest Service research evaluated seed weight variation to show that: (1) environment has very little influence on seed weight, (2) Wyoming and basin big sagebrush subspecies have significantly different seed weights, and (3) seed weight can be used as a diagnostic to assess the proportion of the two subspecies in a seed collection. This research provides land managers with information to put the seed in the right place.