The form of leaves, variations in which are largely influenced by rainfall and temperature and can be used in palaeoclimatological studies. In simple studies the percentage of leaves with entire (i.e. not serrated) margins indicates temperature (e.g. if 68–70 per cent of leaf margins are entire the mean annual temperature (MAT) is 20°C, a deviation of 4 per cent in the proportion of entire leaf margins indicating a temperature deviation of 1°C), and the length of leaves is related to the availability of water. For more reliable interpretation, these measurements are used in conjunction with other factors (e.g. the percentage of leaves with apices that are attenuated (drip tips) rather than rounded; the size of mesophylls, notophylls, and nanophylls; and the ratio of leaf length to width). Studies of leaf physiognomy have indicated that both temperature and rainfall increased substantially at the commencement of the Tertiary.
Subjects: Ecology and Conservation.