Gnetae are any of the species of plants in the taxonomic division Gnetophyta. The division contains three orders with 70 overall species, and are located all over the world, from deserts to tropical rain forests. Many of these can be used as food and have medicinal properties. One species can even be made into a tea. The main thing that the plants in phylum gnetophyta have in common is their reproductive structure and process. Other than this there's almost nothing to connect the three diverse orders under this strange class. 
The three orders under Gnetophyta have similar reproductive characteristics, but their physical characteristics are widely varied. They do share some physical characteristics though, because the xylem in all gnetophytes contains vessel cells, and all gnetophytes have decussate leaves (a pattern that has successive leaf pairs that are perpendicular). Other than this they are all very physically diverse.
Order Gnetum typically grows as vines but it has species that grow as shrubs or trees. The broad leaves are decussate and pinnately net-veined, and their vine-like stems have swollen nodes.  Bract-like scales have stems that bear spiky compound cones. 
Order Ephedra grows as shrubby plants that are also known as joint firs. Their leaves are decussate and have the appearance of being in whorls. Their stems are green when young and have many joints. The cones typically grow from the axils on the leaves and have single stamens joined together to form a compound cone. 
Order Welwitschia has only one species. Many describe this plant as having "bizarre" characteristics. The taproot gives way to a short stem that has branches and leaves coming out. The branches are short and woody with two (rarely three) leaves that grow from a basal meristem for the entire life of the plant. These leaves are decussate and strap shaped and the branches are unbranched. They have red pollen cones that grow on the branches and ovulate cones that grow from the roots. 
Gnetophytes are typically dioecious - having plants with either male or female reproductive structures. The male structures are typically found as compound cones with bracts and the female reproductive structures are "flowers" with one (rarely two) ovules pointing upwards, a nucellus with two to three coats, and a long micropyle in the shape of a tube.
The sperm itself isn't flagellated and therefore doesn't have the ability to move. In order for pollination to take place, the micropyle from the eggs extends and attaches itself to the pollen tubes in order for fertilization between the gametes to occur. The gnetophytes exhibit double fertilization when they fertilize. This means that two male nuclei are involved during the fertilization process, but one will disintegrate while the other will become a seed without an endosperm covering. 
Each plant order is found in different areas of the world. Welwitschia has only one species in its order and it grows only in the Namibian desert in south west Africa. The plant uses the stomata on its leaves to absorb water from passing fog. During droughts antelopes and rhinos use the plant leaves as food.
The order Gnetum is found in the tropical forests of west and central Africa. It is of commercial importance for the inhabitants there as it is valued as a quality food source and a treatment for several illnesses..
Lastly, the Ephedra are native to the North American West, but they can be found in arid, desert-like areas. They are sometimes called "Mormon Tea" since they can be prepared as a tea with medicinal properties. They are also used as herbs with stimulant properties. 
As noted in the ecology section, the members of gnetophyta are useful as a food and a medicinal herb.
Order Ephreda can be made into a "Mormon tea" when the dried leaves are strained into boiling water. This tea was used to treat mild ailments such as fever, headaches, hay fever, and colds. It is now an ingredient in some over-the-counter medications today. It has been used for over 4000 years to treat problems such as respiratory problems and asthma.
The plants in order gnetum are used as a crop for commercial trade. The leaves can be harvested as a valuable vegetable and it is actively farmed in East and West Africa. Like order Ephreda it is also used to treat a variety of ailments including an enlarged spleen, nausea, sore throat, warts, and boils. The stem is sometimes cut up and used as a way to reduce the pains of childbirth. 
- Phylum Gnetophyta Jack R. Holt. Taxa of Life.2010
- Gnetaceae The Gymnosperm Database.2010
- Ephreda The Gymnosperm Database.2010
- Welwitschia mirabilis The Gymnosperm Database.2010
- CH 22 Gymnosperms Kellogg Community College.1999
- Phylum Gnetophyta University of Wisconsin.2009
- Welwitschia Mirabilis Alice Notten.Kirstenbosch National Botanical Garden.March 2003
- Tea Time in the Desert DesertUSA.com and Digital West Media, Inc. 1996
- Gnetum domestication for livelihood improvement and conservation Charles Tekwe, Nouhou Ndam and Joseph Poteh Nkefor.XII World Forestry Congress.2003