Gigantopteridales

Description

Gigantopterid plants had simple, bilaterally symmetrical leaves, woody stems, and spines, and they produced new parts by shoots. Their fronds resembled fern fronds when young but matured into leaves with reticulate venation. For instance, Gigantopteris nicotianaefolia has leaflets shaped like tobacco leaves. They grew at least 20 cm tall, possibly over 50 cm, depending on whether they were scrambling vines or erect.

Some species preferred wetlands, while others thrived in arid habitats. Their vascular tissue contains vessel elements, resembling that of Gnetophyta in some taxa, and they had a cuticle similar to other seed plants. Male sporangia (Gigantotheca) and seeds (Gigantonomia, Cornucarpus) have been tentatively assigned to this group. Chemical analysis shows they produced oleananes, compounds otherwise known from flowering plants, though also found in some modern ferns.

At least some gigantopterids were climbers; Gigantonoclea is thought to have twined around the tree fern Pecopteris in a helical pattern.

Systematics

Gigantopterids are probably a non-monophyletic form taxon, as plant life from their era is difficult to organize. They have been variously allied with seed ferns (Peltaspermales, Callistophytales), Gnetum, and Magnoliophyta, but currently can only be classified as spermatophytes. They are unlikely to be close relatives of acrogymnosperms, cycads, or ginkgos, as those lineages were already distinct in the Late Permian. Vegetative leaves of Emplectopteris were once included but are now placed in Emplectopteridaceae within Callistophytales.

Some experts propose the name Gigantonomiales for presumed core taxa, but many remain skeptical until more is known. Several genera have been assigned to the family Gigantopteridaceae with numerous subfamilies by Gen-ichi Koidzumi; some of his divisions may prove useful. However, even if Gigantopteridales is verified as a clade, the family would likely be more narrowly circumscribed, possibly limited to the two genera in Gigantopteridieae. Named genera include Cathaysiopteris, Gigantonoclea, Gigantopteris, Gothanopteris, Gigantopteridium, Palaeogoniopteris, Zeilleropteris, Delnortea, Emplectopteridium, Emplectopteris, Neogigantopteridium, and Vasovinea.