Peltigera Britannica

Day 136: Peltigera britannica is fairly easy to distinguish from other similar lichen species in the field when it is fruiting. Its cephalodia (layman's term: "little black spots") are easily detached. In fact, they are so easily detached that a good rainstorm can complicate identification by removing them. Each cephalodium is capable of reproducing another lichen, and large masses of Peltigera are not uncommon where conditions are ideal. This lichen attaches to its substrate by means of rhizines which, although they resemble roots, do not absorb nutrients. They serve solely to hold the lichen in place on rock, tree trunks or soil. The same species can exhibit a brown upper surface, many times growing side-by-side with a spring-green companion.

Peltigera Britannica

Day 109: Any of my regular readers will vouch for the fact that I love lichens. In fact, I refer to them as the "wildflowers of winter" because so many of them come into fruit during the cold months of the year. Peltigera britannica is an example. If you look closely at the photos, you will see that the green surface of its lobes are flecked with tiny black dots. These are its cephalodia, small gall-like propagules which are at this point composed of cyanobacteria. Britannica's cephalodia detach easily when mature, often washing off during rainy periods. They then capture the same green algae (Nostoc) found in the parent lichen, and begin to develop lobes of their own. This lichen may also reproduce through the spores contained in its "painted-fingernail" apothecia (photo, right). Many lichens demonstrate more than one reproductive strategy, insurance for their survival.

Cephalodia Scrape-Test

Day 128: New word for you: cephalodia (SEF-uh-LO-dee-uh, singular "cephalodium"), i.e, "a small gall-like growth that contains cyanobacteria and occurs within the tissues or on the surface of some lichens with green algal photobionts." What the definition neglects to mention is that each cephalodium is a reproductive structure, in essence a mini-lichen which when detached, can reattach to the substrate and become a full-sized specimen.

"Detach" is the keystone word in this story. When I first discovered this colony, it was quite dry and the cephalodia were firmly attached to the thallus. Consequently, I misidentified it as Peltigera aphthosa. After the lichen had rehydrated some months later, I happened to brush against one of the lobes while examining something else, and noticed as I drew back that the cephalodia had fallen from one section. I tested another area with a swipe of my finger. Sure enough, the little black dots wiped away easily. "Well!" says I. "You're britannica after all!" (Parkie friends are used to me talking to natural objects.)

Compare the areas circled in red in these two photos. Although lightly attached, the cephalodia were easily scraped off by my thumbnail, leaving behind small white dots (the green algal photobiont came away with them). This is a quick and easy field test which will separate these two confusing Peltigeras. Yes, I cleaned them out from under my thumbnail and left them where they could continue to reproduce.

Common Freckle Pelt, Peltigera Aphthosa

Day 101: Nothing excites me more than finding and identifying something I haven't previously catalogued. It doesn't have to be a rare species, although that's certainly a bonus. It just needs to be new to me. As many times as I've walked around Longmire Campground, I have failed to notice the abundance of this "pelt" lichen until today when the brilliant green thallus drew my attention during a rather wet lunchtime patrol. Later on my walk, I discovered several colonies in fruit, the large mahogany-brown apothecia sticking up like little flags. The scattered cephalodia (greyish-black dots which contain cyanobacteria) are what give this lichen its common name, Freckle Pelt. It is one of four species which host a green algal photobiont, the photosynthetic component of a lichen. In Peltigera aphthosa, this component turns brown when dry or when exposed to sunlight, undoubtedly the reason I overlooked it until now.