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''Cyathea cranhamii'' is an extinct species of tree fern. It was described based on permineralised sori from the Early Cretaceous deposits of Apple Bay in Vancouver Island, British Columbia. ''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". Numerous ''Cyathea'' species are present today in the Americas, especially the Greater Antilles, the Caribbean, and Central and South America. ''C. cranhamii'' is named after Gerald Cranham of Parksville, British Columbia, who provided plant specimens for study at the University of Alberta. ==References== *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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cyathea cranhamii」の詳細全文を読む スポンサード リンク
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