Eocene Green River Horsetail Cone Plant Fossil

The Green River Formation deposits of Wyoming, Colorado, and Utah are best known for their immaculately-preserved fish, but other examples are known as well, as this specimen attests. This is an example of a strobilus (cone-like structure) of a scouring rush or horsetail known as Equisetum. The tip shows the sporangiophores which bore the spores by which the plant reproduced. The modern-day examples have been used to clean cookware due to their high silica content. The deep brown color is a fine contrast to the light shale matrix. The extant Equisetales are represented by the single genus Equisetum. Fossil examples are often denoted by the name Equisites. Whichever name is used, they are a mere shadow of the immense Equisetales that existed in the Carboniferous, some of which grew to be in excess of 10 meters tall.