Gigantopterid

They bore many of the traits of flowering plants, but are not known to have flowered themselves. Gigantopterid plants had simple, bilaterally symmetrical leaf structures, woody stems and spines. They grew new parts by producing shoots, like flowering plants. Judging from the fossil remains, they were probably robust plants with fronds that resembled fern fronds when young. When mature they were more like flowering plant leaves with reticulate venation arranged in a frond. Gigantopteris nicotianaefolia for example is named thus because each of its leaflets resembles a tobacco leaf in shape. They grew at least over 20 cm (around 10 in), probably over 50 cm (20 in) tall, depending on whether it grew as a scrambling vine (the initial assumption) or erect (nowadays considered more likely). Some apparently preferred wetlands, while others throve in rather arid habitats. The vascular tissue contains vessel elements and in at least some taxa resembles that of the Gnetophyta. They had a cuticle similar to that of other seed plants. Some male sporangia (Gigantotheca) and seeds (Gigantonomia, Cornucarpus) have been tentatively referred to this group. While the sporangia are certainly not flowers, they differ from other sporangia of Permian plants. Chemical analysis of fossil remains indicates that gigantopterids produced oleananes, chemical compounds otherwise known to be used by flowering plants, for which they function as a suppressant of insect pests. They are apparently also found in certain modern ferns however. ==Systematics==

It is probable that the gigantopterids are a non-monophyletic form taxon. Plant life from their era is very difficult to document and organize. They have been variously allied with the "seed ferns" (another paraphyletic group of early seed plants) Peltaspermales and Callistophytales, Gnetum, and the Magnoliophyta. All that can be said at present is that they were spermatophytes. It is also highly unlikely that they were close relatives of acrogymnosperms, cycads or ginkgos, because these lineages were already established and distinct in the Late Permian. However, many experts remain skeptical of the new name, because they consider such a move premature until more is known about the interrelationships of the genera of "gigantopterids" and the relationships of these to other plants. It appears as if at least some of his divisions ought to prove useful when a more definite phylogenetic, systematic and taxonomic arrangement for this group is eventually found. On the other hand, the Gigantopteridaceae would with near certainty have to be more narrowly circumscribed even if the Gigantopteridales are by and large verified as a clade; they might even become limited to the two or so genera now placed in the Gigantopteridieae. Proposed subfamilies and genera Cathaysiopteridieae - may be synonym of Palaeogoniopteridieae • Cathaysiopteris • Cathaysiopteridium Gigantopteridieae (including Cardioglossieae) • Gigantonoclea - includes Cardioglossum and apparently Progigantopteris • Gigantopteris Gothanopteridieae - may be synonym of Cathaysiopteridieae/Palaeogoniopteridieae • Gothanopteris Palaeogoniopteridieae • Gigantopteridium • Palaeogoniopteris • Zeilleropteris Unresolved • Delnortea • Emplectopteridium • Emplectopteris • Neogigantopteridium - probably Cathaysiopteridieae/Palaeogoniopteridieae • Vasovinea == Use as palaeoclimate proxies ==

Gigantopterids, like the angiosperms of the late Mesozoic and Cenozoic eras, have been used as proxy estimates for palaeoclimate through a process known as foliar physiognomy. Palaeohydroclimate can be estimated based on gigantopteran leaf size, with greater leaf size generally indicating greater precipitation. Additionally, the percentage of entire margined gigantopterid taxa in a palaeobotanical assemblage has been suggested to be a function of palaeotemperature. ==See also==