Cordaixylon dumusum n.sp. (Cordaitales). I. Vegetative Structures

Cordaitean remains are a prominent component of the vegetation at an Upper Pennsylvanian coal-ball locality in eastern Ohio and form the basis for reconstructing both endarch and mesarch cordaitean plants. The plant with endarch xylem maturation has small stems that produce abundant adventitious roots, spatulate leaves, and Cordaianthus-type cones. It is reconstructed as a small shrub and assigned to Cordaixylon Grand'Eury as C. dumusum n.sp. Structure and variation in the stems, leaves, and roots are described. Primary vascular architecture of the stems forms a sympodial system identical with that of extant conifers with helical phyllotaxis. Leaves range from needle-like with a single vein to spatulate with numerous veins and are borne in heteroblastic series. On some stems, there is a rapid transition from the needle-like leaves at the base to spatulate forms at more distal levels. On other small stems, needle-like leaves are produced throughout. Leaves are borne in a helical fashion, and trace divergence indicates that they approach 3/8, 5/13, and 8/21 arrangements, the larger stems having the more complex fractions. Branching is axillary, and root-trace xylem diverges at the nodes between the levels where leaf traces and branch traces emerge. Cordaixylon dumusum is the first cordaitean plant to be characterized from Upper Pennsylvanian deposits and the only cordaitean thus far reconstructed in full.