Callixylon wendtii sp. Nov., a new species of archaeopteridalean progymnosperm from the Late Devonian of Anti-Atlas, Morocco

Abstract

Archaeopterid trees were the main components of most Late Devonian forests. Their aerial axes characterised by a eustele with mesarch primary xylem strands, leaf traces departing radially from cauline bundles and secondary xylem tracheids with radial pits arranged in groups, are referred to the genus Callixylon Zalessky. The nineteen species of Callixylon described to date from North America, North Africa, Europe, Xinjiang and several parts of Russia range from the late Givetian to the Mississippian. In this paper, we describe a new species of Callixylon from two specimens collected in the Famennian locality of Mader el Mrakib in eastern Anti-Atlas. Callixylon wendtii sp. Nov. is characterised by the presence of sclerotic nests in the pith, a new character for the genus. Its wood shows narrow rays of variable height, with unevenly distributed ray tracheids. Small vascular traces crossing the wood within the two innermost growth rings are interpreted as evidence for short-lived leaves. This discovery adds to the diversity of the genus Callixylon in an area of northern Gondwana that may have been favourable to the establishment of a diverse community of archaeopterid trees.