Seed anatomy and development in cycads and Ginkgo, keys for understanding the evolution of seeds

Cycadales and Ginkgoales constitute two of the most ancient lineages extant seed plants as such are prime candidates for study evolution seeds genes involved. The ovules these plant formed by a single massive integument that, ovule matures into seed, is comprised stony layer covered fleshy coat. However, literature on their morphology anatomy, which key understanding land plants, scarce not easily accessible. Here we provide review highlighting diversity megastrobilus morphologies. Additionally, present further morphological anatomical descriptions, making comprehensive description ovulated structures in Cycadales. In general, similar amongst species, with three well differentiated zones: sarcotesta, sclerotesta endotesta, from outer zone to inner zone. Cycad have sets vascular bundles: one sarcotesta another region between endotesta nucellus (i.e., pachychalaza). Ginkgo does any vasculature ovule. Other differences species that mainly related number cell layers abundance location ergastic substances.