Fossil foliage of the horsetail (Equisetophyte) *Annularia stellata* preserved in a concretion from the Pennsylvanian of the Mazon Creek area of northeastern Illinois (PRI T-1762). Note the whorls of leaves around the branch. *Annularia* is one of the foliage taxa for extinct, tree-size horsetails (Calamitaceae). Specimen is from the teaching collection of the [Paleontological Research Institution](http://www.priweb.org), Ithaca, New York. Length of surrounding rock is approximately 15 cm. Model by Emily Hauf.