A nutritious but famously unpleasant root vegetable from the Delta Quadrant, which Neelix worked into stews, broths and many other dishes served in Voyager's mess hall.
Leola root is Neelix's staple ingredient and the crew's standing complaint. It is rich in vitamins and minerals and grows on many worlds along Voyager's route, which makes it valuable to a ship that has to ration replicator power, but hardly anyone can stand the taste.
It is first gathered in the episode State of Flux, when an away team is collecting food on a planet shortly before a Kazon ship is found nearby. From then on it turns up in the mess hall as stew, broth, tea and garnish.
Jokes about it run through the whole series. Officers plead for anything else, and being served leola root becomes shorthand for the hardships of life far from home, though Neelix never stops insisting that it is good for them.