ABSTRACT
In 1827, Robert Brown proved the gymnospermy of Cycadales and Conifers. The word Gymnosperms refers to the polyphyletic group of plants with naked ovules. The Angiosperms or flowering plants appeared during the lower Cretaceous close to the equator. Gymnosperms and Pteridospermatophytes dominated the earth’s surface at that time. Gymnosperms seem particularly poorly adapted to rapid colonization of new and unstable environments. Flowering plants classically constitute a branch named Magnoliophyta that was divided into two classes: the Monocotyledons and the Dicotyledons, on the basis of various morphological characters such as leaf venation, number of cotyledons, mery, or number of pollen apertures. Monocotyledons appeared during the upper Cretaceous. They issued from a protomagnoliidian trunk of woody plants with imperfect vessels. Reproductive apparatus is as Gymnosperms but without grouping in cones; stamens with many pollen sacs, ciliate antherozoids; ovule with a pollen chamber; seed of the Cycas type.
