I'm aware of experiments using extremophiles, though not lichens. The Martian atmosphere, being almost pure carbon dioxide, would probably be ideal conditions for plant life and would make seeding the planet with suitable lichen spores or whatever for the purposes of oxygenation a viable possibility. I would be surprised, in a nice way, if anything could be grown in the Martian soil, which to the best of my understanding is far too oxidised to sustain life (though having said that: http://www.space.com/12695-mars-soil-lif...study.html). We live in interesting times.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'
