Citrus is one of 31 Rare Resources in the game and available from the beginning. It appears as an orange/tangerine tree with a cart and some baskets full of fruits. Like all rare resources on land, Citrus can be obtained by sending a Merchant from the Market to the resource location. Citrus provides the following benefits:
Healing effect Editrepaired at a rate of 1 hit point per 1.33 seconds and a flashing green 'glow' appears under the ship each time a hit point is restored. At this rate, most ships would take 3–4 minutes to get all their hit points restored.
The healing rate from citrus is slower than the repair rate of the Dock. The repair rate at the Dock can also be improved by researching Herbal Lore, Medicine, and Pharmaceuticals at the Granary. Ships garrisoned inside a Dock can be repaired in less time (with all three upgrades five times faster). So especially in the late game, it might be more effective to pull damaged ships back to a dock for repairs.
Also note, that transport vessels like the Transport Barge do not profit from this resource (and also cannot be repaired at a dock).
The healing effect of Citrus stacks with the natural healing of Aircraft Carriers.
Sometimes, citrus appears on land maps where there are no oceans thus reducing its effectiveness.
The effect of ships healing at sea when supplied with citrus is due to the fact that citrus prevents scurvy, a disease especially common on ships from the 15th to the early 19th century. Moreover, possibly due to the fruit and bark of citrus trees, this rare resource can contribute to the production of food and timber.