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Populus tremuloides is the most widely distributed broadleaf forest tree in North America. However, aspen are declining rapidly in areas of the Intermountain West. Aspen in this area are prone to experiencing limited moisture and high temperatures. An important aspect of plant physiology when dealing with these stressors is stomatal function. Stomata control the rate of photosynthesis, therefore, the size and frequency of the stomata is likely to influence the survival of the species in this environment. An unusual feature of aspen is the high frequency of triploidy in the southern portion of its range. Stomatal size and frequency differences between cytotypes have not been assessed in aspen. The purpose of this study is to evaluate the differences in stomatal length and frequency between diploid and triploid aspen in Utah. If stomatal size differences are pronounced between cytotypes, this could be the basis of a rapid field-based test to distinguish cytotypes without laboratory analyses. To test this, I collected leaves from independent clones in Logan Canyon and Fish Lake National Forest in the summers of 2013, 2014, and 2015. Through flow cytometry I determined the ploidy of the trees. Using cellulose acetate impressions of the underside of the leaves I measured the stomatal size and frequency. Based on my preliminary analysis, there is a difference in stomatal size and frequency between clones rather than between cytotypes. Understanding the complexities of the different aspen ploidies is essential in future forest management and prediction future vegetation changes in a changing climate.