Fossil Plant | Annularia sphenophylloides | Spain

Annularia sphenophylloides
Late Carboniferous (~305 myo)
León Province
Spain

Plant approx. size: 2.25" x 2.25"

Matrix approx. size: 11.75" x 6.5" x 0.75" at thickest part. Average thickness approx. 0.5".

Annularia sphenophylloides is the foliage (leaf whorls) of the extinct Calamites, an arborescent (tree-like) horsetail that flourished in Carboniferous coal swamps. The plant bore leaves in distinct whorls around the stem nodes. In A. sphenophylloides, the leaves are typically narrower at the base and broader at the tip, and are arranged in whorls of 10-20. They measure about 5-15 mm long and are relatively short compared to other Annularia species.

The whorls often show a star-shaped or wheel-like appearance in compression fossils, which made them distinctive. The venation is simple, consisting of a single prominent midvein running from base to tip.

Calamites grew along rivers and wetlands, reaching heights of over 30 feet. Their rapid growth and ability to spread through underground stems helped them dominate the lush coal swamp ecosystems that later formed many of today’s coal deposits.