Turning the corner, the roots twist condense, leading to a basal nexus underground. This must be the spot where Nayadra poisoned the tree. It looks kind of like a taproot, but larger than any you've ever seen, and partially rotting away. Jekaena clasps the book and grimaces...
"Ah, I think the reward Hurzevarkh was offering was to let you live. But I also think he's not planning to follow through on that one. Anyway, we're here. I'll get to work, but it'll take a while. Our enemies will be upon us before I've completed this task. I need to borrow Carrow briefly, but I think I can get him back to you before we're under attack..."
I posted an updated map with the corner and the heart chamber in the Discord. The fountain represents the taproot, and should be considered a floor-to-ceiling obstacle for movement/vision in the chamber. Jekaena must remain adjacent to the taproot, but you may position all other party-members however you like in preparation for defending her. Assailants can arrive from all four directions, either through the corridor you've just traversed (you did leave two pathways unexplored on your way here) or through the root maze that makes up the other three walls of this chamber.