Leon himself talks about his plant that it is his best friend as he never complains and they have in common that they don't have roots.
He always cares for his plant, as he doesn't only include his plant in his day routine, but also saves it in the dangerous scene at the end of the film. You wouldn't save some general plant in that situation. Matilda also plants it at her school where she names it Leon, too.
So I bother what's about the plant. Does the plant have more to do with the story what I can't see? Is it maybe a reference in real life on one of those persons? Or is it just the fact that Matilda tries to let his memory live on by giving the plant "endless life" by planting?
For what does the plant in Leon The Professional really stand?