One Fungus - Two Lichens

Valentine's month comes to an end, and here we have another blog about lichen relationships. Lichens are a symbiotic relationship between a fungus and a green alga or a cyanobacterium. However, the reality is not that simple. Green algae and cyanobacteria have different physiological properties, allowing lichens to grow in different microhabitats. In addition, cyanobacteria are able to fix atmospheric nitrogen, which comes handy in nutrient-poor environments. While most lichens feature either a green alga or a cyanobacterium, some lichen fungi manage to associate with both at the same time. In such cases, the primary photobiont is a green alga and cyanobacteria are usually found in small pockets within the lichen, often invisible from the outside. Yet, occasionally the same fungus can form lichens that either contain green algae or cyanobacteria in separate lobes. This is shown here with the example of Pseudocyphellaria rufovirescens, a lichen common in New Zealand that usually forms lobes with green algae but often starts out associating with cyanobacteria. The two associations look very distinct and suggest that different lichen fungi are involved, but the only difference is the photobiont, which apparently then causes the lichen fungus to produce morphologically distinct lobes. The genetic base for this distinction is unknown and is subject of a collaborative project recently started by Field Museum lichenologists.