Polyxylon australe ̵1 a New Cladoxylalean Axis From the Devonian of Australia

Abstract

Two well preserved axes discovered in the Late Devonian Mudstones at Barraba, New South Wales, Australia, have an anatomy resembling that of Polyxylon elegans described in 1939 by Read and Campbell from the Late Devonian New Albany Shale of Indiana, U.S.A. in the northern hemisphere. We have erected a new species, Polyxylon australe, for these larger axes from the southern hemisphere.

From our study of the anatomy of both the Australian and American axes we agree with Leclercq, who in 1970 grouped Polyxylon with the Cladoxylopsida. However, in Polyxylon australe the protoxylem appears to be exarch at the tips of the xylem arms while in most other members of the Cladoxylopsida the protoxylem seems to be confined to a peripheral loop in each radially aligned vascular segment. The occurrence of two species of the one genus with similar anatomical structures, geographically at great distance from one another, raises some interesting questions of Late Devonian phytogeography.