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Image Title: In the indusium of Cyathea cranhamii
Image Credit: Selena Smith, University of Alberta, Gar Rothwell, Ohio University, Ruth Stockey, University of Alberta
Intended End User: Teacher, Student
License Details: BSA - Terms for Image Use
Copyright held by: Selena, BSA
Date Created: 7/1/2002
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About the Image

Tree ferns occur throughout the world in predominantly tropical habitats. The group has a long history and is known since the Jurassic, ca. 160 million years ago. Fossils of this family, Cyatheaceae, are usually carbon imprints (called compression fossils) of leaves. Other fossils, such as the stems of tree ferns, are petrified, with the organic plant material mostly replaced by minerals. This image of the indusium of Cyathea cranhamii Smith, Rothwell et Stockey shows sporangia with spores. Spores are triangular with a trilete mark. The sporangia have areas with thickened cell walls (the annulus), which help in dehiscence (the opening of the sporangium) and spore dispersal. Sporangial stalks are visible as small clusters of four to six cells in cross section. Cyathea cranhamii comes from late Cretaceous (ca. 130 million years ago) sediments of British Columbia, Canada and represents the first known permineralized reproductive tree fern material.

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