“The interaction between two different organisms living in close physical association, typically to the advantage of both”
My Christmas cactus and African violet both sit year-round on the windowsill in the kitchen. The Christmas cactus blooms several times every year. The African violet blooms only once a year, but every time it blooms, the Christmas cactus also blooms.
This year the Christmas cactus bloomed in late November rather than at Christmastime. But as soon as the African violet began to bloom in January, the Christmas cactus bloomed again. In fact, whenever the African violet is in bloom, the Christmas cactus is sure to follow.