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Trichloris crinita and T. pluriflora are perennial grasses native from Argentina that have productive potential as forage for arid and semi-arid regions. The objectives of the present work were to analyze in both species the variations in leaf stomatal distribution and density under two different water regimes and their association with rainfall at the place of origin. Six introductions for each species were characterized. Two trials were implemented, one in a humid environment and the other in a dry environment. Measurements of foliar dimensions and stomatal counts in each material for each environment were made. The Principal Component Analysis represented 73.3% of the variation on the first two axes, responding to the effect of the evaluation environment on stomatal parameters and to the differences between species for their foliar dimensions. Significant differences were observed between introductions of T. crinita in both environments for most of the variables analyzed. Variations between introductions of T. pluriflora were observed only in humid environment. The observed variations correlated with rainfall at the collection site only for T. crinita. The variables used here were useful for the characterization of the materials analyzed: their implications for the conservation of this plant genetic resource are discussed.