The effects of edaphic moisture in anatomical characters were evaluated in two different populations of Carex hirta L. with three watering treatment for 6 months to evaluate stability, and determined taxonomic value. Water availability increased (p<0.001) leaf thickness from 239 to 289μm, metaxylem vessel diameter from 17 to 23μm, air cavity size from 10 to 24% and adaxial epidermal cell height from 18 to 34μm, and abaxial from 11 to 16μm, adaxial epidermal cell length from 54 to 105μm, and abaxial from 35 to 86μm, and adaxial epidermal cell width from 20 to 33μm, and abaxial from 15 to 23μm. Stomatal index and the number of cells in the girder of sclerenchyma did not vary with water availability, hence these traits have taxonomic value. Other characters (the length and amplitude of wall undulations in the epidermal cells, the number of bulliform cells) have a doubtful relation with water availability, because they are variable even in constant homogeneous conditions.