The Vegetative Anatomy of Schopfiastrum decussatum from the Middle Pennsylvanian of the Illinois Basin

Schopfiastrum decussatum, a monostelic pteridosperm, has been recovered from Middle Pennsylvanian age coal balls from six localities within the Illinois Basin. Additional features of stem anatomy include the presence of horizontal sclerotic plates in the inner cortex, secretory ducts in the inner and outer cortex, and adventitious roots. The primary xylem is interpreted as bilobed, emitting massive leaf traces in a distichous manner. Five orders of frond members are described, including pinnules. All orders of the frond contain secretory ducts and tissues characteristic of Schopfiastrum stems. The rectangular, bilobed protostele, and method of leaf trace origin indicate that Schopfiastrum is more closely related to certain lower Carboniferous seed ferns than to contemporary Pennsylvanian pteridosperms.