A New Reconstruction of the Iridopteridalean Ibyka amphikoma Skog et Banks from the Middle Devonian of Gilboa, New York State

Premise of research. Clarifying the basic anatomy and morphology of Devonian fossils is essential for understanding the origin and radiation of land plants in deep time. Iridopteridales is a major Devonian plant group for which there is no presently established whole-plant concept.Methodology. The type material of the iridopteridalean Ibyka amphikoma Skog et Banks was reprepared and redescribed to clarify the details of its branching patterns and enable comparison to the previously described anatomy.Pivotal results. At least three orders of branching are known. Insertions of laterals are dominantly whorled, sometimes imperfectly, with distinct internodes. Within a whorl, branches may substitute for dichotomous appendages, with the latter more numerous. A new reconstruction is presented. On the basis of the partially preserved anatomy and the comparison to anatomically preserved Iridopteridales, we infer that traces to the branches and appendages are emitted one from each arm of a multiribbed actinostele. This pattern contrasts with that of the only other iridopteridalean preserved both anatomically and morphologically, Compsocradus laevigatus Berry et Stein, in which traces are emitted from alternate ribs in each whorl, with angular offsets between adjacent whorls.Conclusions. This basic understanding of the essentially whorled organization of Iridopteridales, as well as their overall morphology and anatomy, will benefit attempts to infer the broader phylogeny of early land plants, including the origins of horsetails and ferns.

Automated summary

Clarifying the basic anatomy and morphology of Devonian fossils is crucial for understanding the origin and radiation of land plants in deep time. Investigation on the iridopteridalean Ibyka amphikoma Skog et Banks helps to clarify its branching patterns and enable comparison to the previously described anatomy, providing valuable insights into the phylogeny of early land plants.