The Opera HTHC screening system provides a performant system to detect and count stomata on leaf samples. We have applied this method to the detection of stomata in several monocots, including maize and its close relative Teosinte, as well as two Brassicaceae species, Arabidopsis thaliana and Biscutella didyma. Results have revealed both genotypic and environmental variation have a significant impact on the density of stomata on the leaf surface. Comparison with phenotypic measurements of growth and drought resistance have established the adaptive and agronomic relevance of this trait.