A Systematic and Developmental Analysis of Arthropitys deltoides Sp. Nov.

Abstract

Arthropitys deltoides sp. nov. is described from Pennsvlvanian sediments of southeastern Kentucky. The axes are characterized by parenchymatous interfascicular rays that broaden conspicuously toward the periphery of the wood and secondary tracheids with diameters that are more than twice as large as any yet described in Arthropitys. In addition, there is a well-developed rhytidome composed of several concentric periderm lamellae. The species is compared with other late Paleozoic calamites that possess persistent interfascicular rays, and the differences between them are described. Based on the presence of broad parenchymatous zones in the wood, large-diameter thin-walled tracheids, and the relatively small size of the axes, it is suggested that A. deltoides was a liana. An analysis of the secondary xylem reveals that there is a marked ontogenetic increase in the size of the secondary rays and the width of the individual parenchyma cells. The data suggest that analyses of this type are important in distinguishing between developmental and taxonomic variation and that such an approach may prove useful in characterizing individual calamite species and, ultimately, in assessing systematic relationships within this group.