Grottonus
Grottonus was a planet.
In 2381, Lieutenants jg Beckett Mariner, Brad Boimler, D'Vana Tendi, and Sam Rutherford were assigned to investigate moss inside a cave on Grottonus. During the away mission, they were trapped inside the cave when tremors collapsed the entrance. While attempting to contact the USS Cerritos, they discovered that the cave moss was carnivorous and sentient, and interested in hearing stories of their past adventures. Unbeknownst to the four, the situation had been engineered as a morality test by the Vendorians. (LD: "Caves")
The name Grottonus is a play on the word "grotto", or cave.