In the rainforests of Central America lives a small gentian flower, Voyria tenella. Their flowers are a vivid blue, and their stalks pale white. These ‘ghost plants’ have no leaves, nor any trace of green. In the place of branching, exploratory root systems they have clusters of fleshy fingers that sit like small fists in the shallow soil. With no leaves and no green pigment, Voyria plants are unable to eat light and carbon dioxide in the process of photosynthesis. Their stubby rootlets are ill-suited to absorb water or nutrients from the soil. How, then, can Voyria survive?
A few years ago, I travelled to Panama to study the symbiotic relationships that form between plants and the fungi that live in their roots, known as mycorrhizal fungi (from the Greek mykes, meaning fungus, and rhiza, meaning root). More than 90 per cent of terrestrial plants depend on these partnerships. They are a more fundamental part of planthood than flowers, fruit, leaves, wood or roots, and lie at the base of the food chains that sustain nearly all terrestrial life. Fine threads of tubular fungal cells – known as mycelium – emanate from plant roots into the surrounding soil. These cells can link different plants in shared networks that have come to be known as the Wood Wide Web. This is how Voyria are able to make a living. Through shared fungal networks, nutrients and energy-containing sugars pass into Voyria from neighbouring plants. Mycorrhizal associations are so prolific that between a third and a half of the living mass of soils is made up of mycorrhizal fungi; their mycelium is a living seam that helps to hold the soil together. Globally, the total length of mycorrhizal mycelium in the top ten centimetres of soil is around half the width of our galaxy. In 1845, Alexander von Humboldt described the ‘living whole’ of the natural world using the metaphor of a ‘net-like, entangled fabric’. Mycorrhizal fungi make the net and fabric real.