Male Cone Evolution in Conifers: Not All That Simple

Abstract

Despite the simple structure of male conifer cones, there is an enormous variability in cone properties observed upon more careful examination. The diversity ranges from simple cones to compound cones. Moreover, cones can be distinguished according to different spatial distributions on the tree. Simple cones are distributed either as solitary cones or as fascicular or clustered aggregations, while compound cones only exhibit fascicular or clustered aggregations. Here, we demonstrate that these different spatial distribution patterns correlate with distinct leaf types and variable branching frequencies. Furthermore, we provide new insights into the evolution of the sporangiophore, particularly in Taxaceae. Two notably important and fast-evolving characters of conifers are the number of sporangia per sporangiophore and the number of sporangiophores per cone. We demonstrate, across many species and types of cones, how these characters are able to adjust according to the optimal amount of pollen.