The 'sign-eating' tree on Malaga's Camino Nuevo

Few are those who stroll along Camino Nuevo in Malaga in the summer. The long steep, street that connects the Victoria neighbourhood with El Limonar and the La Caleta beach turns away anybody in this hot weather.

If you do take a walk, however, you will notice a curious natural phenomenon right next to the bus shelter. A sturdy London plane tree is 'devouring' a works exit sign that was hung on it years ago by workers. The only word you can see now is 'camiones', as the rest of the sign, with the words 'Salida de' has already been swallowed by the tree, as if it were its a prey.

The tree's jaws have a firm grip and it would not be easy to remove the sign. It is already part of the plant.

The tree has encysted the metal plate as a self-defence mechanism. Botanist and professor of biology at the University of Malaga (UMA) Enrique Salvo says that the tree is reacting to a foreign body. "At certain times in their growth, some trees generate a protective tissue called 'parenchyma', which has enveloped this sign," he explains.

According to the scientist, not all trees act this way in the face of external threats. "We can find some plants that integrate other plants, but in this case the voracity of the specimen is striking, as it gobbles up a metal element." The result is the formation of a large callus around the threat, i.e. the road sign, to prevent pathogens from entering the plant.

Other species have similar mechanisms, as in the case of galls formed in response to insect bites. In some cases, symbiotic systems develop in which the insect bites and the tree encapsulates it, "but together they form a type of structure that serves as mutual defense", as occurs with oaks, terebinths, and certain mastic trees, among others.

As Enrique Salvo points out, the transport of raw sap and processed sap takes place near the surface (although there is a common misconception that it happens through the central core). "In this case, what the tree has solved with this conglomerate of rough tissue is the problem of allowing the sap to keep flowing upward."

Therefore, the plant will probably try to close the callus definitively until the sign is completely covered. In many cases, these processes lead to a weakening of the tree. However, in this case, the botanist observes that the process has taken place very quickly, in a period of between three and five years - a rapid reaction that has prevented this anomaly from interfering with its vital development through the spread of infections.