Most botanists view the breeding systems of angiosperms, with pollen tube competition, genetic incompatibility systems, and diverse floral mechanisms that decrease inbreeding (e.g. herkogamy and dichogamy) as “sophisticated” compared with those of nonflowering seed plants. However, nonflowering seed plants exhibit a variety of developmental systems that may minimize inbreeding and promote maternal mate choice or interpaternal competition. In conifers, archegonia are always initiated after pollen has been received by the ovule and pollen tubes have germinated. It has long been known that the number of archegonia initiated per female gametophyte in each conifer species is variable. For example, in Pinus banksia (Pinaceae), two or three archegonia are initiated per female gametophyte; while in Widdringtonia cupressoides (Cupressaceae), between 40 and 70 archegonia are formed. Unfortunately, there is virtually no data that bear on the issue of male gametophyte – female gametophyte developmental interactions in conifers; and it is not known whether the quantity or genetic quality of pollen received by an ovule can affect the number of archegonia initiated. In Pseudotsuga menziesii (Pinaceae), greater numbers of pollen tubes and higher numbers of archegonia within an ovule do yield significantly more fertilization events per ovule. Given the constraint that each conifer seed typically matures only a single embryo (or aborts), increased numbers of sirings (of genetically identical eggs) within an ovule produces an arena in which paternal genomes and their potential compatibility with a specific female gametic genome are more stringently selected. What is now needed is comprehensive study of the developmental biology of breeding systems in conifers within a framework that appreciates the conserved phenology of pollination prior to archegonial initiation, the potential importance of phenotypic plasticity of archegonial number, and the key role that post-fertilization interembryo competition may play in shaping the paternal genetic contribution to the next generation.

Key words: conifer, gametophyte, mate choice, outcrossing, phenotypic plasticity