Forming Attachments

Day 48: At some point in my illustrious career, I identified this lichen as Parmelia hygrophila, and I choose to believe that I would not have ventured out onto a limb without being 99% sure. This post, however, is not so much about one particular species, but about forming attachments, and trust me, lichens are amazingly good at it. They can grab onto almost anything: wood, rock, bone...even metal or plastic, as can easily be seen on my garden gate (above) and the vinyl siding on my house. All it takes is a film of dust and a tiny bit of texture/porosity, the latter not something one generally associates with painted surfaces. The trick to their tenacity lies in rhizines, root-like structures on the underside of their lobes. In many cases, these rhizines are too fine to be seen with the naked eye. Unlike roots, though, rhizines are not concerned with nutrient uptake. They're there solely to hang on, and if you were to try to peel this delicate Parmelia away from its metal friend, you'd be in for an argument which might surprise you with its vehemence.

Forest Zombies

Day 83: This is how spooky stories begin: hands clawing up through the soil, wrinkled and darkened skin peeling back in shreds, yellow fingernails overgrown and seeking out victims. The Forest Zombies are coming to get you! You have to admit that the Peltigeras have a corner on "creepy" when it comes to their morphology, but the "fingernails" are in fact the apothecia (spore-producing structures) of these common lichens. Some "Pelts" are difficult to tell apart. Others, like Peltigera membranacea (Membranous Dog-lichen, above) are fairly easy, with naked-eye observation of the rhizines (root-like structures on the back of the lobes) being definitive. You should be able to tell it from any others, at least if you're brave enough to get close to a Forest Zombie.

Peltigera Membranacea

Day 177: You might wonder (as did I) why Peltigera membranacea is referred to as a "dog-lichen." One source claims that it is because the rhizines resemble a dog's fangs. Whether this is accurate or not, I can't say, but it makes sense in a left-handed sort of way. The Peltigeras were once believed to be a remedy for rabies, based on what is known as the "doctrine of signatures," i.e., that herbs and plants having a similar appearance to a body part can be used to treat an affliction of that part. The resemblance of the rhizines to canine fangs suggested being bitten by a dog, therefore the lichen must have been useful against hydrophobia. Kids, don't try this at home! The "doctrine of signatures" is a myth, and a dangerous one at that.

So, that said, the "fangs" of Membraneous Dog-Lichen are the clue to its identity. Other lichens may share the same upper-surface characteristics, but only Peltigera membranacea has rhizines growing singly rather than in clusters or groups. This can be seen quite clearly in the righthand photo. These structures are often mistaken for roots, but their true function is to attach the lichen to its substrate. Many lichens have rhizines, although some can't be seen without a magnifier.

Peltigera Membranacea, Membranous Dog Lichen

Day 90: Although they resemble roots, rhizines such as those found on the undersides of Peltigera lichens, these non-vascular structures do not play a role in the lichens' uptake of nutrients. Rather, they are what attach it to its substrate material. They occur in many forms and sizes: hairlike, forked, branched, bottle-brush; short, long, dense, sparse and so on. The morphology of the rhizines is diagnostic in many foliose lichen genera, so a hand lens is a valuable tool to have in the field. In this instance, we have Peltigera membranacea, commonly known as Membranous Dog Lichen. Why "Dog?" The common name has always baffled me, so I turned to the internet for help with the mystery. According to Encyclopedia Britannica, it addresses the resemblance of the fruiting bodies to dogs' teeth. Personally, I think they look more like zombie fingernails.

Dichotomously Branched Rhizines

Day 1 of YEAR EIGHT! I'm going to start you off with a couple of those big "science words" I throw around so freely because it's crucial to know what to look for if you're trying to identify this particular common lichen. Parmelia hygrophila grows on tree bark and is grouped with others as "shield lichens," meaning that they form a mass which adheres closely to the substrate (i.e., the bark, in this case). We refer to this as being "tightly appressed," but that's a feature shared with a lot of other lichens. The words I'd like to introduce are "rhizine" and "dichotomous." "Rhizine" refers to the root-like structures on the back side of the thallus (body). Sometimes these structures are so fine that you need a microscope to see them. At the very least, you need a hand lens to tell how those of the Parmelias branch. Enter "dichotomously," i.e., they form two-pronged forks ("di-" means "two").

Looking at these under a 20x stereo microscope, it's easier to identify individual rhizines if you view a piece of the thallus from the top and observe where they stick out along the sides. Viewed from the bottom, they just look like a mass of tangled threads. Note the inset in the upper left. See how some of the threads have split ends? That's "dichotomous branching." Parmelia hygrophila exhibits dichotomous branching, as opposed to its look-alikes P. saxatilis (unbranched) and P. sulcata, which has squarrulose ("bottlebrush") rhizines. We'll save "squarrulose" for another day.

Rhizines

Day 200: Peltigera membranacea (Membranous Dog-Lichen) provides an excellent lesson in how lichens attach themselves to a substrate by means of root-like structures called rhizines which grow out from the back side of the thallus. In Peltigera, the rhizines are large and obvious; in the finely crustose lichens which occur on rock, they may be invisible without the aid of a hand-lens and yet if you were to try to peel one away, you'd soon discover why they are also referred to as "hold-fasts." Most lichenologists agree that rhizines do not assist in tranferring minerals or nutrients to the body of the lichen, although this has not been proven conclusively. Others suggest that close attachment to the host aids in retaining moisture.

Peltigera Rufescens, Field Dog Lichen

Day 27: Of any Peltigera I might have thought I'd find at Layser Cave, Peltigera rufescens wouldn't have made the list. This beautiful silver-grey pruinose pelt is normally considered a "dry-side" species, but its dense rhizines ("forming a contiguous mass") separate it from any other of its kin. After I got past the "Oooooh, what's that?" stage of discovery, the next words out of my mouth were, "Man, have you got rhizines! You's a woolly bugger! And aren't you gorgeous!" Then, with a look over my shoulder as I remembered that there had been a couple of other hikers on the trail below me, I settled into the serious business of documenting my find. Of course I didn't know it was rufescens at that point, and since I was in National Forest territory (Forest, as opposed to Park), I had only slight reservations about nipping a 1" x 1" specimen for analysis at home in case there were specifics I'd only be able to see under the microscope. I needn't have worried. The rhizines were definitive, and bingo! a new lichen for my Life List.

Analyzing Umbilicaria Vellea

Day 256: When lichens are dry, they are much less easy to identify in the field. That it was an Umbilicaria was not immediately obvious because the "belly button" effect is not pronounced in this species, but as I removed a sample, its single point of attachment became clear. With the issue of genus settled, the real work began to determine species. I narrowed it down to two, and then threw up my hands and sent photos off to a lichen contact at the UW. Under her direction and using a microscope, I was able to confirm that it was Umbilicaria vellea, a less common and smaller lichen than U. americana (from which it has only recently been separated as a distinct species) and more likely to be found in an alpine environment. A closer look at the rhizines (inset) will reveal tiny black granules which may serve as vegetative propagules for the lichen.

Nesting Nidula

Day 59: One day I returned a little late to the office after a lunchtime walk and was explaining to Kevin that I had been sidetracked by a specimen of Hemitomes congestum while searching for Drosera rotundifolia, blathering on about the uniqueness of the find and the proliferation of mycoheterotrophic species I had been observing through the months of spring, only to have him say, "Crow, I have no idea what you're talking about." It pulled me up short and made me see that while I was throwing around botanical names and terms as casually as if I had been talking about Fred and George, most people are a bit uncomfortable with scientific jargon. I realize now that it might be easier on my readers if I provided a glossary, so let me give you one to accompany this photo of one of my favourite fungi, Nidula niveotomentosa, aka "Bird's-Nest Fungus."

Very often, the Latin name of a species will tell you something about its characteristics. In this case, "-tomentosa" refers to the presence of a tomentum, a velvety or woolly texture found on the surface of a plant. The view through the microscope at the top left shows this attribute...a fuzzy-wuzzy nest for the "eggs" which give this family of fungi its common name. The "eggs" (shown in the nest in the center 'scope view) are called peridioles. These contain spores. The bottom 'scope view shows the peridioles liberated from the "cup," appropriately called a peridium.

On the right, you can see the Bird's-Nests in situ alongside a flourishing colony of Peltigera membranacea, a member of the family of Pelt lichens. The translucent structures which appear like stalactites on the underside of the "leaf" are rhizines, a root-like structure which attaches the lichen to its substrate of rock, wood or soil. If you think fungus-jive is hard to wrap your tongue around, lichen terminology is another breed of cat. We'll get to that in future posts.

Pelt Rhizines

Day 85: While the discussion of pelt lichens is still fresh in my readers' minds, I thought another view of Membranous Dog-Lichen might be appreciated. If you thought their top sides were strange, this is what you would see if you turned one over. These threadlike structures are called rhizines, and they serve as roots to attach the lichen to wood or rock. Like any other root, the rhizines allow the organism to draw nutrients from the substrate.

Don't forget to stick a magnifier in your pocket the next time you go out for a nature walk! You never know what you might find.