The female gametophyte of gymnosperms is a multicellular structure serving the functions of bearing the archegonia and nourishing the developing embryo. It exhibits a progressive series of significant changes leading towards angiosperm conditions. Due to the absence of fossil records,…
Gnetales is an order of the gymnospermic seed plants. This order is composed of three genera- Gnetum, Ephedra, and Welwitschia. Chamberlain (1935) has placed all three genera in a single-family Gnetaceae. But Markgraf (1951) has been split up the order…
Coniferales is a gymnospermic order like Ginkgoales. The members of this order form the common conifers. The order Coniferales includes both fossil and present-day living genera. The Coniferales reached their maximum development probably during the late Jurassic period or the…
Ginkgoales is a special gymnospermic order having one living genus (Ginkgo biloba). The members of this order once had an almost worldwide distribution in the Jurassic period. The fossil members of this order probably appeared in the Devonian period of…
Cycadales is a gymnospermic order. Members of this order are mostly inhabitants of tropical and subtropical regions. Cycadales include both living and fossil genera. They originated in the Mesozoic era and continued up to the Jurassic and Cretaceous periods. Only…