Temporal range: Carboniferous
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 8-13 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 32 feet (10 meters).
Specimen of Annularia stellata from Italy on display at the Museo Civico di Storia Naturale di Milano
The foliage of Calamites