MORPHOLOGY AND SYSTEMATICS OF CORDAITES OF PENNSYLVANIAN COAL SWAMPS OF EURAMERICA

Cordaites are extinct coniferophytic shrubs and trees of the Late Paleozoic. They were most prominent in tropical coal swamps existing from the Westphalian A-B boundary of Western Europe to the middle Desmoinesian (Westphalian D) of midcontinental United States. Structurally preserved coal-ball cordaites from Pennsylvanian Euramerican coals were analyzed for whole plant understanding, morphological variation, and indications of ecological tolerances. Organ assemblages for individual species were established from coals where coal balls contain single cordaitean seed species. Cordaitean organ assemblages were stratigraphically compiled, compared, and cross-correlated.;Other cordaitean assemblages examined included Mesoxylon from the lower Westphalian A of Lancashire, England; the lower Middle Pennsylvanian of eastern Kentucky; and the lower Desmoinesian of Iowa.;Cordaitean assemblage comparisons of most known coals with coal balls confirm organ assemblages established for Pennsylvanioxylon, and indicate that Mesoxylon bore Mitrospermum ovules. Mesoxylon and Pennsylvanioxylon are the only coal-swamp Pennsylvanian cordaitean genera recognized herein. They are consistently different in stem xylem development, leaf and branch trace formation, in amount of cortical sclerenchyma and associated organs. Morphology of coal-swamp cordaites, especially cortical aerenchyma in Pennsylvanioxylon, indicates semi-aquatic ecological adaptation. Coal-swamp cordaitean lineages may demonstrate both gradualistic and punctuational evolutionary changes.;Two Pennsylvanioxylon species assemblages occur in Middle and Upper Pennsylvanian coals of the Illinois Basin Coal Field. The Pennsylvanioxylon birame assemblage was reconstructed from specimens of an unnamed western Indiana coal that is approximately equivalent to the Illinois Murphysboro Coal Member. Pennsylvanioxylon birame is a small tree (LESSTHEQ) 5 m. tall with a basal diameter (LESSTHEQ) 7 cm. It bore Cardiocarpus spinatus ovules, Cordaianthus concinnus fertile shoots, Cordaites principalis leaves, and Amyelon iowense roots. The Pennsylvanioxylon nauertianum assemblage from the Summum (No. 4) Coal Member of northern Illinois includes Cardiocarpus oviformis ovules, Cordaianthus duquesnensis fertile shoots, and leaves and roots similar to the assemblage of the Ohio Duquesne Coal Bed. Reconstructed plants are small shrubs (LESSTHEQ) 1 m. tall. Pennsylvanioxylon birame occurs in the lower Desmoinesian in the Interior Coal Province of the United States. Pennsylvanioxylon nauertianum occurs in the upper Desmoinesian in the Interior Coal Province, in the Missourian of Illinois, and the Conemaugh of Ohio.