AbstractThe relationships between the vegetative leaf dimensions, nerve width, proximal and median lamina cell dimensions, maximal alar cell width, and leaf curvature within the complex aroundDrepanocladus aduncus(Hedw.) Warnst. andD. polycarpus(Voit) Wamst. were evaluated in two sets of specimens: (1) material that was cultivated to evaluate variation within one clone, and (2) seventy-eight herbarium specimens, including most of the described variation within theD. aduncus-polycarpuscomplex. Within theD. aduncus-polycarpuscomplex most of the quantitative leaf characters studied show a statistically significant weak to strong correlation with each other. More strongly curved leaves are negatively correlated with the measurements of the other characters, otherwise the correlations are positive. The strongest significant correlation occurs between the median lamina cell length and the leaf length (r2= 0 97, single clone, r2= 0.92, herbarium material; based on median values for the character measures), but also for several other characters r2>0.50 were found. Median lamina cell length, which is often used to separateD. aduncusandD. polycarpus, and leaf length are thus two aspects of the same character. In the second specimen set, the variation of several other studied parameters, e.g. proximal lamina cell length and nerve width, are to a large part explained by the size variation of the plants. Taxa previously recognized within theD. aduncus-polycarpuscomplex cannot be circumscribed using characters studied in the present investigation, and it is suggested that new characters must be found if more than one species,D. aduncus, is to be recognized.