Introduction

Abstract

Indubitable seeds first appeared in the Devonian (395–359 my B.P. = million years Before Present). These seeds are not enclosed in ovaries, as in flowering plants, and are designated naked. This character is the basis for grouping a large number of varied plants as a natural group, the Gymnospermae (gymnos = naked, sperm = seed). Palaeobotanical evidence suggests that the seeds evolved independently in more than one group of Palaeozoic plants and diversified rapidly during the Lower Carboniferous (345 my B.P.). In the course of their evolution, the seed plants have tended to evolve a variety of structures to protect the ovules. Some of these evolutionary “experiments” were successful, and provide insight into the origin of the carpel, while others ended in extinction (see Stewart 1983).