The phylogeny of angiosperms presented by various authors is based principally upon our knowledge of modern plants. The fossil history of flowering plants has had little influence upon current concepts of primitive features of the flower. Several reproductive characters of non-angiospermous plants demonstrate the diversity of flower-like characters common to some extinct major groups of plants. Various Lower and Middle Cretaceous angiosperm reproductive structures illustrate the nature of the early receptacles, carpels and perianth parts. Pteridosperms (seed ferns), which bore separate clusters of ovules and microsporangia are considered a likely ancestral source of the angiosperms. Probable radiations of both diclinous (unisexual), mainly wind-pollinated, and monoclinous (bisexual), mainly insect-pollinated, lines are suggested for the ancestral flowering plants. The primitive flower types are thought to be quite simple with subsequent elaboration and other modifications of the flower, resulting from the adaptive ecological strategies of reproductive mechanisms through time. Insects have played a major role in floral evolution but not to the exclusion of ancient wind-pollinated forms. There have been major and minor shifts of the reproductive ecology in various groups of angiosperms so that the diverse flowers and fruits seen today are the product of reticulate patterns of evolution. © 1979.
