Annularia is a
form taxon name given to leaves of
Calamites. In that species, the leaves formed radiating leaf whorls at each stem node, in a similar way to the branches of
Equisetum, an extant genus of
horsetails.
Annularia leaves are arranged in whorls of between 8 and 13 leaves. The leaf shape is quite variable, being oval in
Annularia sphenophylloides and linear to lanceolate in
Annularia radiata, but they are always flat and of varying lengths.
Calamites were arborescent and grew to a height of . ==Fossil records==