The gnepine hypothesis is a modification of the gnetifer hypothesis, and suggests that the gnetophytes belong within the conifers as a sister group to the Pinaceae.
Carlquist studied wood anatomy of the Gnetophyta and was an author of many plant taxa, including species of the carnivorous plant genus Drosera, the Western Australian genus Stylidium, and the odd Australian genus Alexgeorgea whose female flowers are almost entirely underground.