Article: Cortical development in Chaloneria cormosa (Isoetales), and the biological derivation of compressed lycophyte decortication taxa
Kathleen B. Pigg and Gar W. Rothwell
Several anatomically preserved stem fragments showing a wide range of surface features have been discovered among specimens of the Upper Pennsylvanian isoetalean Chaloneria cormosa. A comparison of the specimens demonstrates that stems produced a narrow zone of periderm, and that tissues external to the periderm accounted for a moderate increase in stem circumference by two distinctive modes of cell divisions. Depending on the presence or absence of secondary cortical tissues, on differential taphonomy, and on the level at which the cortex is exposed, the surface of a specimen may be comparable to one of several distinctive decortication morphotypes. The outer surface is similar to Bothrodendron and Cyclostigma, while specimens with leaf bases removed are reminiscent of Stigmaria. When fractured through the periderm a Knorria surface is produced, while secondary cortical features immediately external to the periderm conform to Asolanus. Specimens reveal the anatomical bases for decortication morphotypes and demonstrate that such genera are produced by members of Isoetales as well as Lepidodendrales.