This study examines the variation of bark thickness within and among populations of baldcypress [Taxodium distichum (L.) Rich. var. distichum] and pondcypress [T. distichum var. imbricarium (Nuttall) Croom] to determine its usefulness as a taxonomic character. Baldcypress from 14 populations and pond- cypress from eight populations were sampled for bark thickness and trunk diameter. Significant difference was observed in the relation of bark thickness to diameter between the two taxa. When bark thickness to diameter (BT/D) ratios were analyzed, the ratios for baldcypress ranged from 1.2 x 10-2 to 8.9 X 10-2 with a mean of 3.2 x 10-2, while the BT/D ratios for pondcypress ranged from 3.7 x 10-2 to 12.5 x 10-2 with a mean of 6.6 x 10-2. Bark thickness ratio may be a useful diagnostic character when classifying populations when used in conjunction with other characteristics, but it should not be used exclusively for classifying individuals. A correlation between bark thickness and habitat type may exist, and the thicker bark of pondcypress may provide higher tolerance to fire and hydroperiod fluctuations.