Relationship between fungus and alga in the lichen Cladonia cristatella Tuck

Abstract

The nature of the lichen symbiosis is not clear. It is generally thought to be mutualistic but this concept is not supported by experimental evidence¹. Early workers^2,3 considered that .lichens represented algae parasitized by fungi—as evidence, they noted algal cells in a lichen thallus that were dead or penetrated by fungal haustoria. Others, however, cited the seemingly healthy and long-lasting nature of lichens as evidence of mutualism. As we report here, our observations of artificial syntheses of the mycobiont Cladonia cristatella (‘British soldiers’) with different algae suggest that the relationship in this lichen is one of controlled parasitism. The mycobiont formed squamules mostly with algae related to its natural phycobiont, an indication perhaps of a long period of co-evolution between the symbionts of this lichen.