Is Shape of a Fresh and Dried Leaf the Same?

<div><p>Plants kept as dried herbarium specimens share many characteristics with their living counterparts, but there are some substantial differences between them. Due to dehydration, leaves of herbarium specimens change not only their mass and colour, but in many cases change their dimensions, too. The present study aimed to determine whether leaf shape changes during the drying process. A total of 794 pairs of fresh and dried leaves or leaflets of 22 plant taxa were studied. The shape of the blades was quantified using elliptic Fourier analysis combined with principal component analysis. In addition, area and mass of the leaves were measured. Statistical tests were applied for comparing fresh and dried leaves. The results indicate that the preservation process of pressing and drying plants for herbarium purposes causes changes in leaf shape. In general, the shape changes were directional. As the shape of fresh and dried plants is different, it is strongly recommended that shape analyses should be performed on datasets containing either of the leaf types.</p></div

Scatterplot for results of principal component analysis of elliptic Fourier descriptors.

<p>Small circles indicate position of fresh leaf shape in the PC1–PC2 morphospace, while the lines show the shape change. Individual scatterplots are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0153071#pone.0153071.g002" target="_blank">Fig 2</a>. Patterns of variation along PC1 and PC2 axes are shown on the top and on the left of the plot, by a mean shape and shapes +2 and -2 standard deviation (SD) distant from the mean.</p

Relationship between relative area loss and shape change expressed as vector length.

<p>Mean values for species were used, with 95% confidence of fit.</p

Values distribution of sine and cosine of the angles between shape-change vectors and the principal component 1 (PC1)-axis.

<p>Mean values marked with black points. The sin α values correspond to direction of the vector along PC1-axis, while cos α values correspond to its direction along the PC2-axis. All sin α means are positive, which points out that there exists a strong generalised tendency of directional shape change toward lower values of PC1. No general trend has been detected in cos α values, although strong tendencies can be observed for some species.</p

Shape changes resulted from principal component (PC) analysis of elliptic Fourier descriptors for fresh and dried leaves for each group of analysed plants.

<p>Arrows represent shape changes in the PC1–PC2 space. The starting point indicates shape of a fresh leaf and its head corresponds to its shape after drying. Vector lengths are, in general, not comparable between diagrams, as their scaling is not identical. Leaf silhouettes on the right present mean shapes of fresh leaves.</p

Plant material used in the study and significance of differences between groups of fresh and dried leaves in shape parameters, as well as their area loss and mass loss.

<p>Plant material used in the study and significance of differences between groups of fresh and dried leaves in shape parameters, as well as their area loss and mass loss.</p