Placopsis Gelida

Day 261: Bullseye! It's easy to see how Placopsis gelida got its common name "Bullseye Lichen," although the cephalodium is not always as perfectly oriented as it is in this specimen. It is this nitrogen-rich feature of lichen anatomy which makes it possible for Placopsis to colonize the seemingly bare surface of recently broken rock. When wet, this lichen may exhibit a greenish-blue tint. Placopsis is a "pioneer" species, i.e., one of the first to establish itself on freshly exposed surfaces. It contributes to the breakdown of rock and in decay, supplies both the matter and nutrients in which vascular plants can establish themselves. The next time you see a rock cliff dappled with wildflowers, thank the lichens which made it possible for them to thrive.

Placopsis Gelida, Bullseye!

Day 177: Many crustose lichens are easy to overlook. At a glance, they might appear to be an inclusion in a rock face or a mineral deposit on the surface. For example, this specimen of Placopsis gelida (a "bullseye" lichen, ref. Vitt et al) could have been mistaken for a discoloured bit of quartz in a darker matrix when seen from a distance. Up close, the lichen reveals its complex form, brown cephalodia (wart-like structures) dotting the pale green thallus and darker lobes extending like fingers along its margins. Crustose lichens adhere tightly to their substrate material; it would be difficult to lift one of those tiny projections even with a pocket knife.