Drought periods are becoming more extreme worldwide and the ability of plants to contribute towards atmospheric flux is being compromised. Properly functioning stomata provide an exit for water that has been absorbed by the roots, funneled into various cell parts, and eventually released into the atmosphere via transpiration. By observing the effects that weather conditions such as climate change may have on stomatal density, distribution, and functioning, it may be possible to elucidate a portion of the mechanisms trees use to survive longer periods of water stress. This study analyzed stomatal density (SD), stomatal conductance (gs ), CO2 assimilation (A), instantaneous water-use efficiency (WUEi ), and transpiration (E) rates in six native tree species in the Midwestern USA and showed that trees within the same ecotype followed similar trends, but that trees within the same family did not when exposed to identical greenhouse conditions. Naturally drought tolerant tree species demonstrated lower g s and higher WUEi , while intolerant species had higher SD. This study showed negative or no correlation between SD and g s , A, E, and WUEi and positive correlations between E and A and gs and E. Drought periods are becoming more extreme worldwide and the ability of plants to contribute towards atmospheric flux is being compromised. Properly functioning stomata provide an exit for water that has been absorbed by the roots, funneled into various cell parts, and finally released into the atmosphere via transpiration. By observing the effects that weather conditions such as climate change may have on stomatal density, distribution, and functioning, it may be possible to elucidate a portion of the mechanisms trees use to survive longer periods of water stress. (SD), stomatal conductance (gs), CO2 assimilation (A), instantaneous water-use efficiency (WUEi), and transpiration (E) rates in six native tree species in the Midwestern USA and showed that trees within the same ecotype followed trends, but that trees within the same family did not when when exposed to identical greenhouse conditions. Naturally drought tolerant tree species demons This study showed negative or no correlation between SD and g s, A, E, and WUEi and positive correlations between E and A and gs and E.