The earliest unambiguous records of the group date to the Jurassic, and they achieved their highest diversity during the Early Cretaceous.

Ephedra species, known as "jointfirs" in the United States, have long slender branches which bear tiny scale-like leaves at their nodes.

Infusions from these plants have been traditionally used as a stimulant, but ephedrine is a controlled substance today in many places because of the risk of harmful or even fatal overdosing.

With just three well-defined genera within an entire division, there still is understandable difficulty in establishing an unambiguous interrelationship among them; in earlier times matters were even more difficult, with Pearson in the early 20th century discussing about the class Gnetales, rather than the order.

[11] In general the evolutionary relationships among the seed plants still are unresolved, and the Gnetophyta have played an important role in the formation of phylogenetic hypotheses.

[14][15][16][17] Although the most salient morphological evidence still largely supports the anthophyte hypothesis, some more obscure morphological commonalities between the gnetophytes and conifers lend support to the gnetifer hypothesis.These shared traits include: tracheids with scalariform pits with tori interspersed with annular thickenings, absence of scalariform pitting in primary xylem, scale-like and strap-shaped leaves of Ephedra and Welwitschia; and reduced sporophylls.

[7] Some morphological characters that were suggested to unite the anthophytes include vessels in wood, net-veined leaves (in Gnetum only), lignin chemistry, the layering of cells in the apical meristem, pollen and megaspore features (including thin megaspore wall), short cambial initials, and lignin syringal groups.

[2][14][15][18][19][25][26][27][28][29][excessive citations] Several of these studies have suggested that the gnetophytes and angiosperms have independently derived characters, including flower-like reproductive structures and tracheid vessel elements, that appear shared but are actually the result of parallel evolution.

[18] These kinds of major morphological changes are not without precedent in the Pinales, however: the Taxaceae, for example, have lost the classical cone of the conifers in favor of a single-terminal ovule, surrounded by a fleshy aril.