STUDIES OF SPHENOPHYLLUM SHOOTS: SPECIES DELIMITATION WITHIN THE TAXON SPHENOPHYLLUM

Structurally preserved ultimate vegetative shoots and attached foliage of Sphenophyllum multirame and two additional taxa from Upper and Middle Pennsylvanian coal balls are described. Shoot axes of all taxa are delimited by small cube‐shaped epidermal cells and contain three isolated strands of protoxylem tracheids separated by undifferentiated procambial cells. Metaxylem maturation is delayed for some distance below the apical meristem. Branches originate from a single protoxylem strand and are contiguous with the subjacent leaf trace for a short distance. Sphenophyllum multirame is considered a valid taxon. It is suggested that shoot and foliar anatomical characteristics may form valid criteria for species delimitation within the genus, and S. reedae is delimited by such characteristics. An additional form is tentatively suggested as a possible new species. Anatomical similarities between 5. reedae and Peltastrobus reedae suggest that these taxa represent vegetative and reproductive structures of the same plant.