Many species have been described. However, the taxonomy is rather confusing. M. Hieb's Plant Fossils of West Virginia branching axes Calamites M. Hieb's Plant Fossils of West Virginia outer surface with branch scars Calamites sp. Mazon Creek Exhibit, Illinois State Museum Calamites sp. The narrow lancet-like Annularia leaves are placed in whorls, positioned at the nodes.
All leaves lie in one plane and the whorls are circular to oval in outline.
Several dozens of species are distinguished, some of them being valuable index fossils. Annularia radiata M. Hieb's Plant Fossils of West Virginia Annularia radiata M. Hieb's Plant Fossils of West Virginia Annularia radiata Fossils of Nova Scotia Annularia mucronata Plant fossils from the Northen Anthracite Field Annularia stellata Plant fossils from the Northen Anthracite Field Annularia stellata Fossils of Nova Scotia Annularia sp. Mazon Creek Exhibit, Illinois State Museum Annularia sp. The narrow needle-shaped leaves are also positioned in whorl inserted at the nodes but all leaves are directed towards the apex of the shoot. The leaf whorls are laterally compressed.