Observations on the Lower Carboniferous Lycopod Oxroadia gracilis Alvin

Abstract

ABSTRACTA stem-base of Oxroadia gracilis is described showing 12 distal rhizophores and 72 roots. The rhizophores branch in a manner interpreted as dichotomy in successive planes at right angles. Each has a siphonostele which may possess medullary tracheids. Root-traces are monarch and wedge-shaped in section and their departure leaves ramular gaps in the siphonostele. The largest root may have functioned as a tap-root formed earlier than the rhizophores and exogenous. Only two out of ten known rooting specimens show rhizophores.An aerial stem with leaves shows secondary xylem up to the level of the probable second dichotomies.Leaves have slightly decurrent clasping bases forming low cushions and are recurved. Ligules (when preserved) occur in deep cavities of leaf-bases. In the apical region young leaves are small, recurved, and grooved distally below, giving a pseudo-forked appearance in cross sections of the stem.Only incomplete strobili are known.Comparisons are made with ‘Lepidodendron’ saalfeldense Solms-Laubach, and Trabicaulis ftabellilignis Meyer-Berthaud; these are considered co-generic.Oxroadia is recorded from the Oil-Shale Group (late Viséan or Asbian) near Kinghorn, Fife, Scotland; and from the Cementstone Group (late Tournaisian or Courceyan) East Lothian, Scotland; Berwickshire, Scotland; and Northumberland, northern England.