This can be considered the counter-part to the "ancient tree" idea.
If the trees on a patch is killed by poison repeatedly in a certain period of time, there will be a chance that the patch became polluted. Any seeding in this polluted patch will have a chance to grow a mutant tree.
When you harvest the mutant tree, the result is unpredictable - sometimes it gives you jellisacs while sometimes beans. The mutant tree might have limited lifespan; but it sure can satisfy everybody's need - with many surprises. :D