Bark Rash Lichen

Thursday, March 24, 2016

When I walk the forests, I'm drawn to a group of living organism of which I have little knowledge - lichens.

I know their forms, that they are composed of a fungus and an alga, a bit about their reproduction, and that they are often encountered in surprising locations.  I've seen them in our forests, in the Arctic tundra, on rocks in Antarctica, hanging from trees in New Zealand, in the Amazon, and in many other places.

But I almost never know what they are or aspects of their individual natural history.

While attending a memorial gathering for the late and great Jackeen Kelleher Churchill, one of the principal founders of the Louisiana Nature Center, I was talking to Dr. Ronald French as he stood holding a walking stick cut from his nearby Mississippi farm.  The stick was from a trunk of an American holly, Ilex opaca, and adorned with whitish, yellowish, and red splotches.  On examination, I realized that once again I knew these patterns were lichens, but I had no idea what species they were.  I photographed the red ones.

Ron said he noticed long ago the obvious multicolored patterns of American holly trunks, and finds them quite attractive.

When I got home, I sat down with my 795 page, ten-pound lichen tome (Lichens of North America, by Irwin Brodo, Sylvia Duran Sharnoff, and Stephen Sharnoff, Yale University Press). 

I spent the first hour familiarizing myself with terminology specific to ascomycete fungi, members of the Phylum Ascomycota, the primary mycobiont (the fungus half of the relationship; the photosynthetic portion, the alga or cyanobacterium, is called the photobiont).

Here are some of the primary words I needed to understand the lichens I was researching (from Brodo et al.):

• thallus - the body of the lichen; may be crusty, fleshy, or otherwise.
• ascoma or ascomata - the fruiting body of an ascomycete fungus
• perithecium - a type of ascoma, said to be flask-shaped, with a pore opening at its apex
• apothecium - a disk- or cup-shaped ascoma, usually with an exposed hymenium
• hymenium - the spore-bearing area of an ascoma
• lirellae - an elongated, possibly branched, apothecium

Did you make it through the list and are you still here?  Good.

The way I listed these terms is the way I have to work the descriptions:  a word uses another interesting word in its definition, so I have to look up that new word.  Invariably the new word's definition has a yet new word, and so on and so forth.

Fun!  This process makes me a better person.

After an hour of turning pages (Did it really take that long for me to turn 613 pages?  No, but as any good naturalist, I got side-tracked many times), I found the red lichen - the Bark Rash Lichen, Pyrenula cruenta, a richly colored, blood-red crimson with very dark bumps (perithecial warts).  It is a crustose lichen, meaning its thallus is closely adhered to the surface of its host.  It prefers trees with "green" bark (such as hollies and beeches), meaning bark with chlorophyll in or near its surface cells.  There is no evidence that the lichen derives nutrition from the tree's bark, but it is tempting to suspect they do.

The description of Bark Rash Lichens says they are crimson over the entire thallus or in patches on the thallus, and if growing in the shade, crimson around the perithecia.

For an amateur, if one looks at the photo (Photo 742, Brodo et al.), which is all crimson, and then reads the description, there is nothing to suggest that the thallus may be vanilla or yellowish.  However, the keen observations of the good Dr. French informed me that they tend to be bright crimson in the winter and less so, fading to orange, in summer.  This can be seen by the blending of these colors on a uniformly textured shiny smooth thallus (see figure to left).

This is further complicated by the presence elsewhere on Dr. French's walking stick of similarly colored yellowish-beige thalli that contain small, thin, white bun-shaped structures called lirellae instead of the perithecial warts.  We are familiar with this lichen, known as Powdered Script Lichen, Diplolabia (=Graphis) afzelii, which we see on almost every wax myrtle we examine in Jean Lafitte National Park's Barataria Unit.

It always amazes me how a natural history adventure can begin in the most unexpected of social situations.

I now can recognize three species of lichens.  Well, four, but the other is a tropical story and you have to visit www.tropicalnaturalhistory.org to see that spectacular species.

 

 

Dr. Ronald J. French and his favored lichenose walking stick from an American holly, Ilex opaca.
Photo by Flora French.

Bark Rash Lichen, with its characteristic crimson coloration and the raised perithecial warts.
Photo by Bob Thomas.

The maroon perithecial warts on a beige thallus, said to be typical of Bark Rash Lichen growing in shaded habitats.
Photo by Bob Thomas.

Bark Rash Lichen showing the gradation from red to the common yellowish-tan coloration of the thallus.  It may be that red is prevalent in winter, fading to orange or light-red in warmer months.
Photo by  Bob Thomas.

Powdered Script Lichen, Diplolabia afzelii, growing on an American holly.  Note the specialized bun-shaped lirellae where the spores are produced.
Photo by Bob Thomas.