Lichen - an introduction

Hiking up Camelback Mtn the other day I was once again impressed by the proliferation of yellow-green lichen following a good winter rain.  I decided to take some pictures and got a bit of a surprise with some of the results.  This shot is actually from Papago Park (pretty much same sandstone conglomeration as the head of Camelback) and shows the big three. The most common lichen you'll find easily without really looking for them.

Pale green one is a Xanthoparmelia species

Rust one is a Caloplaca species

Yellow-green one is Acarospora socialis

The names alone aught to impress you. That I should be able to identify them - not as impressive. I enlisted the help of ASU Professor Tom Nash to identify these and the others.  ASU is part of the North American Consortium of lichen herbariums.  The ASU website ASU herbarium for lichen  has pictures to help identify lichen, but as they are listed by scientific names and not by colors or other identifying factors, I wasn't about to go through and click species after species to luck upon the correct one.  Definitely a site for those who know a bit about lichens! I never would have dreamed there are so many different kinds of lichen.

What are Lichen?

Simply put, lichen are a combination of algae and fungi.  Algae is found pretty much everywhere in the world - in water, on land, high mountains, low valleys, wet soils and dry places.  Fungal spores can pretty much go where the wind blows, which is also pretty much everywhere in the world, and sure enough, you can find lichen just about anywhere.  They have a unique adaptation and symbiant relationship that allow them to survive even the driest climes. 

The algae conduct photosynthesis and provide nutrients...the fungus uses this to grow, obviously. When it rains after an extended period of drought, the fungus cannot immediately begin growing again - the water begins a process in which nutrients are broken down which in turn both the algae and the fungus use.

There are way more complicated explainations out there and you can google lichen to learn more than you may ever need to know about them. One thing about the algae - there is a simpler bacteria form called cyanobacteria which may be a host. And just as algae & bacteria take on a myriad of colors in their various blooms, so do the lichen.