"Window" Lichens Mimic Highly-Adapted Desert Plants

Lichens come in all colors and shapes, but many lichens are green when hydrated and metabolizing, due to their green algal photobionts. So it is not surprising that lichens are often mistaken for plants, even if they actually represent symbiotic fungi and hence are more closely related to animals. To make the confusion perfect, the internal anatomy of many lichens resembles that of plant leaves, with the photobiont layer positioned in a similar way as the chlorophyll layer in leaves.

Since almost all plants are required to be continuously turgescent, that is, have their cells fully hydrated, those plants that grow in areas with high water stress, such as hot deserts, have adapted to these conditions in various ways, for instance in being succulent. Some plants, so-called "window plants", have developed a particular anatomy that allows them to be buried (and protected) in the ground while receiving light through window-like structures. And not surprisingly, some lichens have adopted a similar strategy: their thalli are furnished with large crystal clusters that guide the incoming light to the deeply immersed (and hence protected) photobiont layer. This adaptation is found in several unrelated species and is here shown with the example of a recently discovered, yet undescribed species of the genus Leucodecton from Hawaii, growing on exposed basalt. In the pictures, the anatomy of the lichen leaves a characteristic pattern on the surface.