This is a very nice 2.3" fossil calyx of a crinoid (Eucalyptocrinus crassus), from the Waldron Shale Formation, St. Paul, Indiana. This is the calyx (body) of the crinoid. It sat atop the stem and held the Pinnule (feeding arms). It is attached to the rock it was found in. This specimen has a number of other fossil fragments contained in the rock. One edge of the rock is flat, allowing for aesthetic presentation without the need for a display stand.
Crinoids, sometimes commonly referred to as sea lilies, are animals, not plants. They are echinoderms related to starfish, sea urchins, and brittle stars. Many crinoid traits are like other members of their phylum; such traits include tube feet, radial symmetry, a water vascular system, and appendages in multiples of five (pentameral). They first appeared in the Ordovician (488 million years ago) and some species are still alive today.