Distinguishing characteristics of the phylum Gnetophyta include the presence of both tracheids and vessels in their xylem tissue, a unique fertilization feature in which a tube grows from the eggs to unite with pollen tubes, and being the only division of gymnosperms that undergo double fertilization. Gnetophyta plants include trees, shrubs, or stumpy, turnip-like growth forms with simple leaves.
The phylum Gnetophyta consists of three genera of woody plants called Gnetum, Welwitschia and Ephedra. Although the three genera are all gnetophytes, they are highly specialized to their respective environments, which makes it difficult to identify similar characteristics.
Gnetum species are mostly woody climbers in tropical forests, although the best-known member of the group is a tree. Welwitschia includes one species, Welwitschia mirabilis. It only grows in the deserts of Namibia and Angola, and has two large strap-like leaves that grow continuously from the base throughout the plant's life. Ephedra plants are known as joint-firs because they have long slender branches with tiny scale-like leaves at each node. Ephedra is traditionally used as a stimulant. The plant and its derivatives are classified as controlled substances in many jurisdictions because of the high risk of addiction, harmful side effects and fatal overdoses.