Article: A new genus of osmundaceous stem from the Upper Triassic of Tasmania
R. S. Hill, S. M. Forsyth and F. Green
Petrified osmundaceous trunks from the Late Triassic east of Woodbury in central Tasmania are assigned to a new genus and species, Australosmunda indentata. This species possesses an ectophloic siphonostele with a parenchymatous pith, but in other respects is similar to Millerocaulis, Osmundacaulis, or Osmunda. Although leaf gaps are absent the stele is deeply indented where leaf traces arise. A. indentata is the first osmundaceous species described which has a stele lacking leaf gaps but a parenchymatous pith, and offers convincing support for the hypothesis that the evolution of the parenchymatous pith and the evolution of leaf gaps in the xylem were independent transitions. Because of the relatively advanced nature of the leaf traces, and the presence of species with leaf gaps earlier in the record (Palaeosmunda from the Upper Permian of Queensland), A. indentata is unlikely to have been an intermediate stage in the development of leaf gaps, but probably represents a relatively advanced species which has maintained a primitive stelar feature.