Mycorrhizal fungi form vast underground networks connecting tree roots across entire forests. A single teaspoon of forest soil contains kilometers of fungal hyphae, creating a communication and resource-sharing internet beneath our feet.
Physarum polycephalum solves network optimization problems equivalent to the Tokyo rail system. Mycelial growth follows nutrient gradients while pruning inefficient branches — a biological implementation of Steiner tree approximation.
Electrical signals propagate through hyphae at ~0.5 mm/s, modulated by ion channels. Trees under pest attack release volatile compounds absorbed by the network and retransmitted — triggering defensive chemistry in neighbors up to 30m away.