Homology and heterochrony in the evolution of conifer seed cones

The homology and evolutionary origins of conifer seed cones have been debated in the plant morphology literature for over a century. Although seed cones are broadly considered to be compound, in which the ovule-bearing structure is a highly modified shoot termed the ovuliferous scale, conifer research over the last several decades has challenged this interpretation for some taxa and raised new questions about the evolution of these reproductive structures. Here I explore (1) whether structures homologous to the axillary ovuliferous shoots of ancient conifers are present in all groups of living conifers, (2) the development and evolutionary origins of the inverted vascular bundles of ovuliferous scales, (3) the role of heterochrony in seed cone evolution and its relationship to functional morphology and pollination, and (4) evidence of parallel evolution of ovuliferous scales among major conifer lineages.