Ledonia III
Ledonia III was the third planet in its star system. This planet was home to an exotic plant.

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. Dr. Bashir took the remaining fungus to the infirmary and cultivated a new batch that could sustain Dax's plant again. ()

Appendices

Background information 

According to the script, the pronunciation for Ledonia was "luh-DOE-nee-a". 

The plant was later re-used and seen again in the Incredible Tales office on Roy Ritterhouse's desk.

According to Startrek.com, the M-class planet Ledonia III orbited a star named Ledonia.   The  located Ledonia III in the Ledonia system.

External link 
 

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Ledonia 03