Plant fossil assemblages are biased samples of the capacity of the once living source vegetation to produce litter (leaves, flowers, pollen, spores, fruits, seeds, twigs, branches, trunks, roots etc.). The “image” that the depositional system “sees” of the vegetation is in terms of isolated plant organs (or parts of organs) that are produced in greater or lesser quantities depending on the organ type. For instance throughout the life of a tree hundreds of thousands of leaves, many millions of pollen grains but only one trunk are produced. Only very rarely do plant fossil assemblages consist of entire or nearly entire plants. Instead assemblages consist of a mixture of organs in various states of completeness derived from a number of different taxa (each of which produces different organs in different relative amounts) growing at various distances from the depositional site.