FOSSIL PLANTS/Angiosperms 421 Figure The 1998 Angiosperm Phylogeny Group classification of living angiosperms at the ordinal level The recognized groupings are based on both molecular and morphological characteristics Some families (not shown) are not placed within orders features, such as the flower, was difficult to assess Second, although the fossil record is replete with information on pollen, leaves, fruit, and wood, the record of flowers is much sparser First-hand information on the nature of early Cretaceous flowers has been hard to find This means that one of the crucial features of flowering plants has remained poorly characterized in early members of the group Also, because most fossils represent organs or plant fragments rather than whole individuals, their implications for angiosperm origins are not always easily interpreted Third, although it is clear that angiosperms arose from within the gymnosperms, there are conflicting ideas on which living or extinct groups of gymnosperms constitute the closest relatives Furthermore, living angiosperms have diverged substantially from related plants in a number of ways This makes it difficult to draw comparisons between, for example, aspects of the angiosperm flower and putative equivalent structures in gymnosperms In other words, angiosperms are divergent, and this obscures their relationships to other groups of plants Fourth, ‘angiosperm origins’ is really a discussion about the origins of two groups, not one, and this can lead to confusion and argument (Figure 6) There is the issue of the origin of the crown group, which is the group that contains all living species and their most recent common ancestor Members of this group typically