Stability of leaf form and size during specimen preparation of herbarium specimens

Abstract

It is common to draw taxonomic conclusions from the analysis of herbarium material and then apply them to living, fresh material. However, some widely used morphological characters are changed during the preparation of specimens and therefore the applicability of morphometric data obtained from the measurement of dried plants is not universal. We tried to estimate quantatively how different leaf characters change during drying. Fresh and dried leaves of ten plant species were measured and scanned to determine how the stability of commonly used absolute (e.g., leaf length) characters, relative characters (e.g., relative position of maximal width) and leaf contour. For the latter, we employed landmark-based thin plate spline (TPS) analysis. We found that all absolute sizes differed significantly after drying (typically decrease original size 0.9–0.8 times), whereas leaf shape did not differ significantly between fresh and dried leaves of most species. Relative characters were more stable then absolute ones but less stable than a form as a whole. We argue that it is essential to provide measures, contours and/or photographs of fresh leaves together with herbarium material, all the more so because in two cases (20%) leaf contour also significantly changed after drying (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)