MCMANUS, H. A.*, E. L. TAYLOR, T. N. TAYLOR, AND L. D. BOUCHER. Department of Ecology and Evolutionary Biology and Natural History Museum-Biodiversity Center, University of Kansas, Lawrence, KS 66045; Department of Biology, University of Nebraska-Omaha, Omaha, NE 68182. - An Enigmatic Axis from the Triassic of Antarctica.
An axis with a complex vascular system is detailed from Middle
Triassic silicified peat of the Fremouw Formation of Antarctica. The
diameters of the four specimens identified range from 1.2 to 2.2 cm;
the longest specimen is approximately 12 cm. In transverse section,
the vascular system of the silicified axis is divided into
approximately 10 to 16 arms, which extend almost to its periphery.
The vascular segments are embedded in parenchyma and occur as single
traces or as segments connected in the center of the axis. These
segments anastomose at varying levels within the axis. Ground tissue
is located in the center of each segmented arm and consists of
parenchyma and small diameter tracheids which are presumed to
represent primary xylem. Secondary xylem borders this central ground
tissue and extends completely around the segmented arms. A cambial
zone is located external to the secondary xylem with poorly preserved
secondary phloem to the outside. Traces are given off by the segments
near the periphery of the axis; these consist of radially arranged
secondary xylem, some with apparent external periderm. The anatomy of
this axis most closely resembles the vascular tissue arrangement of
plants belonging to the Cladoxylales (Devonian-Lower Carboniferous),
but the anatomical differences, in addition to the stratigraphic age,
preclude formal assignment to this or other orders.
Key words: anatomy, Antarctica, Cladoxylales, Triassic