They're opposed to the tree, which stands for the dominant Western reality and all of Western thought, from botany to biology and anatomy, and also gnosticism, theology, ontology, philosophy. The tree exists in a hierarchical order of a central trunk with larger and smaller branches. The trunk forms the connection between all parts, thus in a way limiting connections. A rhizome, on the contrary, can be connected with any other at any point. A tree can be cut down, whereas rhizomes are much less subject to destruction.
Rhizomes can grow again along another line if broken at some point.
Rhizomes are endless, as are desire and the imagination. It can't be exterminated, because it's like a weed. It's the voice of desire and the imagination in a world dominated by material interests and reason. Like weeds, desire can be 'cultivated' for a shorter or longer period, it can be locked up within political organisations or single issue groups, but it can never be weeded out. But it will always find a way to break out.