Mesozoic Cycads & Cycadeoids
Early Jurassic - Late Cretaceous
Understanding the relationships between the component parts of prehistoric plants can be difficult at best. Here I have prepared four illustrations of Mesozoic cycads and cycadeoids, the bennettitales. Cycadophytes are gymnosperms (naked-seed plants) and comprised a significant part of many Mesozoic floras. Pseudoctenis is a true cycad and was common during the Jurassic period, its leaves being found worldwide. Like many living cycads, it exhibited arboreal characteristics, its trunk growing to several metres in height and leaves growing to two metres in length. Indeed, its foliage is so similar to the extant genus Encephalartos, that it may prove to be of the same family. The cone (strobilus) of Pseudoctenis is called Androstrobus.
Nilssoniopteris leaves are slender, often undivided and have been found in association with the thin smooth trunk of Lioxylon. Some researchers debate whether simple Nilssoniopteris leaves belong to a cycad or a seed fern. The component parts of many prehistoric plants are often found and described separately, making their reconstruction more problematic.
Superficially resembling cycads in appearance, the bennettitales were a sister taxon that flourished from the Early Jurassic to the Late Cretaceous. They can be divided into two groups, the Cycadeoidaceae with stout barrel shaped stems and the Williamsoniacea with taller trunks. The name Williamsonia refers to the seed-bearing cone of the plant, and like other bennettitales Williamsonians differ from true cycads in several ways, most notably microscopic breathing pores (stomata) on the underside of their leaves and the presence of pollen-bearing flowers called Weltrichia. Unlike true cyads bennettitalian leaves detached from the trunk at their base, resulting in a column of compressed leaf scars. Williamsonia leaves are of the pinnate Pitilophyllum type while Cycadeoidea leaves are of the Zamites foliage type. The flowering structures of the bennettitales and how they attached to the main body of the plant are still poorly understood.
Ink & graphite on paper.
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