Gnetopsida

Gnetopsida is a small class of gymnospermous plants, containing only a single order, Gnetales, and a single family, Gnetaceae. This group comprises three extant genera: Gnetum, Ephedra, and Welwitschia. Gnetophytes are characterized by their unique reproductive structures, which show some similarities to angiosperms, though they are not considered to be direct ancestors.

The Gnetaceae family is found in tropical and subtropical regions worldwide. Gnetum species are typically woody vines or small trees, bearing broad, net-veined leaves that are unusual among gymnosperms. Ephedra species are more widespread, often found in arid and semi-arid environments, and are characterized by their jointed stems and scale-like leaves. They are known for producing ephedrine, a stimulant. Welwitschia mirabilis is an iconic plant endemic to the Namib Desert in southwestern Africa. It has a short, thick stem and only two persistent, strap-like leaves that grow continuously from the base.

Reproductively, Gnetopsida exhibit double fertilization, a feature shared with angiosperms. However, unlike angiosperms, they do not form true flowers or fruits. Instead, they have cone-like reproductive structures containing ovules and pollen-producing organs. The seed of Gnetopsida is enclosed within a fleshy or leathery covering, which can sometimes resemble a fruit, but is botanically a naked seed. Their evolutionary relationships are complex and have been the subject of much debate among botanists.