Evidence for patterns of distribution from the past
This chapter investigates the methods available for reconstructing past distribution patterns. Palaeobotanical evidence for the past distribution of plants depends above all on the happy chance that many groups of plants are found fossil with their harder parts preserved. In practice two broadly different types of fossil are recognised and these require different analytical techniques in their study. The most commonly recognisable macro-fossils are wood fragments, leaves, fruits and seeds. Methods for their study, extraction and counting are given in the Handbook of paleontological technique. In the main, plant microfossils comprise the pollen grains of higher plants and the spores of lower plants, although such matter as leaf hairs and epidermis and the skeletons of diatoms and desmids are also important. The two key properties of pollen grains and spores which make them as significant as microfossils are their great morphological diversity, which facilitates identification, and the resistant nature of their wall, which promotes their survival in sediments.