Abstract
Today, cycads are a small group of gymnospermous plants with a limited distribution in the (sub)tropics, but they were major constituents of Mesozoic floras. Fossil leaves sporadically found in latest Carboniferous and Permian floras have putatively been ascribed to cycads. However, their true affinity remains unclear due to the lack of anatomical evidence. Virtually all modern cycads have pinnate leaves, but this type of leaf morphology is by no means unique for cycads. Pinnate leaves of Plagiozamites oblongifolius Halle 1927 with well-preserved cuticles showing the epidermal anatomy are here described from the upper Permian Xuanwei Formation of Yunnan Province, Southwest China. The cuticles show a clear differentiation into costal and intercostal zones; stomata are confined to the intercostal zones on both the upper and lower leaf surfaces. The external morphology and the epidermal anatomy of these fossil leaves are closely comparable with those of extant cycads, particularly members of the family Zamiaceae.
Highlights
Cycads are gymnosperms, typically characterized by a usually unbranched woody trunk with an green crown of pinnate, stiff leaves
Pinnate leaves of Plagiozamites oblongifolius Halle 1927 with well-preserved cuticles showing the epidermal anatomy are here described from the upper Permian Xuanwei Formation of Yunnan Province, Southwest China
The fossil leaves described here are characterized as pinnate fronds with obliquely attached leaflets with multiple, more or less parallel veins and deeply sunken haplocheilic stomata, a combination of features typical for fossil and extant Cycadales [1,9]
Summary
Typically characterized by a usually unbranched woody trunk with an green crown of pinnate, stiff leaves. Some leaves and reproductive organs from the upper Palaeozoic have been putatively assigned to cycads. Owing to their unique morphology, the attribution of reproductive organs to cycads is usually undisputed, it should be noted that some fertile remains originally attributed to cycads turned out to be of pteridospermous rather than of cycadalean affinity [6]. Much more problematic is the nature of late Palaeozoic cycad-like foliage, which still rare, is far more common than reproductive organs. Pinnate leaves are not unique for cycads and an assignment of sterile foliage to cycads is often only possible on the basis of cuticles. Only few, very poorly preserved cuticles of late Palaeozoic cycad-like leaves have been described so far.
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