TROPICAL PLANT ENCYCLOPEDIA
Hydnophytum moseleyanum
Ant PlantFamily: Rubiaceae
Origin: Southeastern Asia
The caudex is hollow, and forms a perfect nest for the ants, which protect the plant, and gets home and sweet sap in exchange.
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Link to this plant:
https://toptropicals.com/catalog/uid/hydnophytum_moseleyanum.htm