Leaf venation density as a climate and environmental proxy: a critical review and new data

In palaeobotany, leaf venation density is still primarily used as a taxonomic character although numerous studies on recent plants reveal that leaf venation density may be influenced by various environmental factors. To promote the use of leaf venation density as a palaeoclimate/palaeoenvironmental proxy we give a brief review of these studies and provide some additional data. Our review shows that environmental factors that increase transpiration of plants or decrease water availability also tend to increase the leaf venation density. Based on the analysis of leaves of some recent and fossil plants we found: (1) Venation density may be measured as vein length per area or as distance between veins, but the first parameter is more reliable. (2) Depending on the plant species, leaf venation density may or may not vary with leaf size. This `leaf size effect' has to be taken into account when leaf venation density is to be used as a palaeoclimate/ palaeoenvironmental proxy. (3) No significant effect of a changing atmospheric carbon dioxide concentration on leaf venation density was observed. (4) In Permian seed plants, intraspecific variation of leaf venation density was similar to that observed in modern angiosperms. Obviously, even in these seed plants, leaf venation density can be used as a palaeoclimate/palaeoenvironmental proxy.