Sprecher
Beschreibung
A small filicalean stem, Tubicaulis weiningensis sp. nov., was discovered in the Late Permian Emeishan Basalt Formation of western Guizhou, China. It represents the first record of this genus in the Cathaysian Flora. The new fossil consists of a large central stem surrounded by a few petiole bases and adventitious roots. The stele is an ectophloic dictyoxylic siphonostele with a few leaf gaps. The leaf traces in the cortex change from an initially thick rod-shaped to abaxially curved C-shaped, with the tips incurved. When the leaf trace separates from the stele, it bears endarch protoxylem strands. Irregularly shaped sclerenchyma bundles are distributed in the concave region of the leaf trace vascular bundle. Root traces emerge laterally from the tips of the leaf traces. The adventitious roots extending along the long axis of the stem indicate an erect growth habit of a small fern. Previously reported Tubicaulis species possess a primitive protostele, and from the Early Carboniferous to the Late Permian the stele gradually became parenchymatized. The present fossil exhibits an ectophloic dictyoxylic siphonostele, representing the advanced stele type in the genus. The fossil record shows that from the Pennsylvanian to the Lopingian, the stele of Tubicaulis evolved from a protostele without leaf gaps to a siphonostele with distinct leaf gaps, accompanied by an increase in parenchyma. The future discovery of more types of filicalean stem fossils in western Guizhou will provide further evidence for understanding the evolution of ferns and community paleoecology.
Keywords: fern, Permian, Anachoropteridaceae, stele, evolution, erect growth