Ledonian soil contained a benevolent mycorrhizal fungus that helped the native plants retain water. When the plant life was deprived of this soil, it would quickly die.
Jadzia Dax owned a potted plant from Ledonia III. After some time, all the fungus in the plant's potting soil had almost completely died out. DoctorBashir took the remaining fungus to the infirmary and cultivated a new batch that could sustain Jadzia's plant again. (DS9: "The Wire")
According to the script, the pronunciation for Ledonia was "luh-DOE-nee-a".