Angiosperms — the Culmination of Plant Evolution

Abstract

The precursors of angiosperms are still unknown. All we know is that angiosperms appeared in Lower Cretaceous strata (see Fig. 2-2, page 19), became abundant and varied by Late Cretaceous time and evolved by Eocene time many modern genera. Reports of pre-Cretaceous angiosperms are usually based on fragmentary evidence such as a leaf, a pollen grain, or a bit of secondary wood. None of these specimens can be unequivocally called an angiosperm rather than a gymnosperm, and paleobotanists generally remain skeptical of them. Morphologists, on the other hand, are inclined to view the complexity of the flower and the embryo sac as well as the wide variety of early angiosperms in the Cretaceous Period, as evidence that the group must have had a long period of evolution prior to Cretaceous time. Axelrod suggested that the first angiosperms arose on highlands far back from the coastal plains and so were not preserved as fossils. But unless someone makes the fortunate discovery of an unequivocal pre-Cretaceous angiosperm we must use the available evidence to learn what we can of the first angiosperms and their subsequent evolution.