The discovery of several distinctive root fragments in carbonate petrifaction material from Illinois provides the basis for the investigation of a Middle Pennsylvanian medullosan rooting system. Specimens range from minute rootlets with incomplete primary development, to large axes over 2 cm in diameter with extensive secondary development. The axes are characterized by an exarch actinostele with up to five protoxylem points. The pericycle of small rootlets is surrounded by endodermis, parenchymatous cortex, and epidermis. More mature specimens exhibit periderm at the outer margin of the pericycle, and in the largest specimens the periderm forms the outermost tissue zone. Secondary xylem is extensively developed in large specimens, and completely surrounds the primary wood. The newly discovered specimens are compared with previously described medullosan roots, and possible affinities with the Middle Pennsylvanian species of Medullosa and Sutcliffia are discussed.