Mesoxylon priapi Trivett and Rothwell, sp. nov.

Stems with non-septate, parenchymous pith; leaves approaching an 8/21 phyllotaxis on some stems; leaf traces diverging from margin of pith as two bundles. Leaves up to 5.7 cm wide and 1 mm thick with bluntly rounded margins, comparable to Cordatites felicis. Branching axillary with one vegetative bud, one cone, or one bud and one cone at some nodes. Traces to paired branches originating by division of a single stele in stem cortex. Cones compound, consisting of elongate, rectangular primary axis (ca. 1-2 mm x 4-5 mm) bearing numerous, alternately arranged four-ranked bracts subtending secondary axes. Stele of primary axis rectangular in cross section, having narrow pith and a narrow band of randomly arranged tracheids surrounded by radially aligned tracheids. Cortex two-parted; inner zone of large and small parenchyma cells interspersed with resin or secretory cells with dark contents, and outer hypodermal zone of small, dark, thin-walled cells. Surface of axis irregularly striate. Secondary axes approximately 1 mm wide x 4 mm long, radially symmetrical, bearing up to 28 helically arranged scales; fertile scales (≤5) apical-most and typically bearing four pollen sacs in linear file at tip. Pollen sacs maturing simultanuously and containing Sullisaccites-type prepollen (ca. 75 µm x 95 µm). Basal sterile scales of secondary axes imbricating tightly to ensheath completely fertile apex prior to maturity; at maturity, fertile scales elongated, extending pollen sacs beyond tips of sterile scales.