Definition of "symbiotic"

Orchids rely on fungi to reproduce. Their tiny seeds don't have any on-board nutrients (like beans and apples) and will not germinate until they are infected by a symbiotic fungus which supplies them with food. Known as a protocorm, this tiny orchid-fungus ball grows, turns green and eventually starts to photosynthesise.

2014 April 5, “Quite interesting: A quietly intriguing column from the brains behind QI, the BBC quiz show. This week; QI orchids you not”, in The Daily Telegraph (Weekend), page W22