Top-shaped multiciliate male gametes, and the mature seed which bears only one embryo with two cotyledons, are characterised features of:

Step-by-step solution

Cycads are the gymnosperm having largest top shaped multiciliate male gametes. Conifers have sperm that do not have flagella, but instead are conveyed to the egg via a pollen tube. It is important to note that the seeds of gymnosperms are not enclosed in their final state upon the cone.