You may well be asking why on earth I have started this post with a picture of an underpass, but on a windy day in Boulder here I was.

I have always been fascinated by the life that manages to persist in heavily disturbed urban areas like the plants sprouting through cracks in the sidewalk. While sometimes easy to simply dismiss the life that persists in these places, to wish that native species could be flourishing instead of the non-native weeds, bugs and animals, I think learning what can live in the midst of all of humanity is a worthwhile task. As I set off my soap box I present to you one such organism.

I was quite surprised to see large patches of a yellow lichen growing on some material presumably used to help keep the dirt in place on the retaining wall. I was even more surprised when I looked closer and determined it was a species I had clearly never seen before. When attempting to key out this specimen I had no good answer it asked me what substrate it was growing on! If you believe it construction material wasn’t an option. Presuming I have the species correct in Tom Nash’s excellent Lichen Flora of the Greater Sonoran Desert Region. Vol 3 possible substrates for the species are “on wood, bark, bryophytes, non-calcareous or calcareous rocks.” This to me shows that the species can be rather opportunistic when it comes to where it can grow. Perhaps a reason it chose this man-made material as a home.

Next time you are on a walk through the city and you see a splash of color where you don’t expect take a closer look you may just find a lichen adapting to the new urban environment we have created.

One of the main reason’s I wanted to start writing on lichens is to show others how to start identifying them. So watch out I’m going to get technical down here and describe this lichen.

Let’s start with a description of the thallus. Step one, it has a thallus, this is the yellow portions in the above photo, and is the main body of the lichen. In some of the small crustose species the entire thallus can be hidden within the substrate and only the apothecia are showing. The thallus also has no distinct leaf-like shapes at the edges (non-lobate) and only consists of little individual specks (areolate).

Second step color, yellow and orange lichens are rather distinctive and, in general, are going to belong to only a few groups of lichens. When presented by a new yellow or orange species a chemical test with Potassium Hydroxide solution is a good step. Lichen aficionados call this a K test. Fun fact K is a product used for some dermatological applications and is super easy to buy. Please inform your spouse before they ask why you purchased foot fungus medicine. I digress. Treat a small section with the reagent and it may well turn blood red. If this is true you have a member of the family Teloschistaceae, as was true today.

Next step is describe the reproductive structures (I hope for a full post about this soon). In the last photo we have apothecia disc or cup shaped structures, but looking closer there is more.

Looking closer we see powdery masses on the margins, these are soredia. This powder can disperse in the wind or hitch a ride on an animal and if it find the right place to live a new lichen can form. Lichens are weird, as you may have picked up on, this specimen reproduces both sexually (apothecia) and asexually (soredia). Talk about keeping our options open.

Hopefully those that kept reading learned a new term of two. Identifying lichens can be extremely hard, and a good key is necessary, or even specialized equipment. If you think I blundered this ID (very likely) let me know I would love to know why.