It was described based on permineralised sori from the Early Cretaceous Longarm Formation deposits of Apple Bay on Vancouver Island, British Columbia.

The sporangia contain 64 trilete spores which bear sculpturing on their outer covering (perispore) ranging from irregular granulate or echinate to prominent rodlets.

[1] The specimens used to describe C. cranhamii are the first anatomically preserved tree fern sori known from the fossil record.

Smith, Rothwell and Stockey (2003) state that "they represent the most ancient evidence for fertile structures of the Cyatheaceae and demonstrate that essentially modern species of cyatheaceous tree ferns had evolved by the Early Cretaceous".

[1] C. cranhamii is named after Gerald Cranham of Parksville, British Columbia, who provided plant specimens for study at the University of Alberta.