Temporal range: Early Cretaceous
|Details of the preserved fertile structures of Cyathea cranhamii.|
Smith, Rothwell & Stockey, 2003
C. cranhamii has sori arranged in two rows on narrow pinnules. They are covered by globose indusia which resemble those of Sphaeropteris species in morphology. Sporangia are circinate (ring-shaped) and bear multicellular stalks. They diverge from a basal, vascular receptacle. The sporangia contain 64 trilete spores which bear sculpturing on their outer covering (perispore) ranging from irregular granulate or echinate to prominent rodlets. The annulus is nearly vertical and arranged in a single series. It is not interrupted by the stalk.
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".
- Smith, Selena Y., Gar W. Rothwell & Ruth A. Stockey 2003. Cyathea cranhamii sp. nov. (Cyatheaceae), anatomically preserved tree fern sori from the Lower Cretaceous of Vancouver Island, British Columbia. American Journal of Botany 90: 755-760.