What is "gnetidae"

Gnetidae is a subclass of Equisetopsida in the sense used by Mark W. Chase and James L. Reveal in their 2009 article "A phylogenetic classification of the land plants to accompany APG III." This subclass comprises the gnetophytes. The Gnetidae subclass is equivalent to the division Gnetophyta and class Gnetopsida of previous treatments.