A Woody Lycopsid Stem From the New Albany Shale (Lower Mississippian) of Kentucky

Abstract

A lycopsid axis from the New Albany Shale (Sanderson Formation) of Kentucky is described. The stem, which branches dichotomously, is 45 mm in diameter and is characterized by a relatively narrow parenchymatized protostele, a 3.0 mm-thick cylinder of secondary xylem, a tripartite cortex, and a periderm that is more than 5.0 mm thick. The secondary xylem is composed of uniseriate and biseriate vascular rays and narrow tracheids with scalariform wall thickenings on both radial and tangential walls. The periderm is characterized by elongate, thick-walled cells, some of which broaden tangentially in the outer part of the tissue forming zones that appear wedge-shaped in cross section. Surface features of the axis, including leaf bases, are not preserved. The stem is tentatively regarded as a member ofthe Lepidodendrales in accordance with the numerous anatomical characters that it shares with more recent representatives ofthe order. Because the external morphology is not known, however, the possibility exists that the axis corresponds to a protolepidodendralean taxon currently known only from compression and/or impression remains or some other nonlepidodendralean plant that produced secondary xylem. The extremely narrow profile of the secondary xylem tracheids (relative to other arborescent lycopsids) is interpreted as evidence that the plants grew in a habitat that was substantially drier than the Upper Carboniferous coal swamps.

Lycaugea edieae gen. et sp. nov., a Late Devonian Lycopsid from New South Wales, Australia

“…However, the external features of this species, which has persistent leaves, clearly differ from those of L. edieae. Close to the Devonian-Carboniferous boundary, the taxa with a medullated protostele that have more characters in common with L. edieae are Wexfordia hookense from Ireland (Matten 1989;Klavins 2004), the lycopsid from the New Albany Shale in Kentucky described by Cichan and Beck (1987), and the one from Donetz referred to as "incertae sedis" and reported by Lemoigne and Itschenko (1980). The Donetz specimen, which lacks secondary tissues and is in the same range of diameter as the L. edieae holotype, differs from the latter in its persistent leaves and dentate border of the primary xylem.…”