[lutusp]

Nice sci-fi idea, but the surface conditions on Mars are so hostile that the poor defenseless moss would roll over and die.

* Temperatures nearly always below the freezing point of water, often several hundred degrees lower.

* Very small amount of air pressure, 0.6% that of earth, and no oxygen at all.

* Because of the two factors above, no liquid water at the surface.

* High levels of radiation directly from space (primarily the solar wind) to the surface, for lack of a global magnetic field. Astronauts visiting Mars will also need to protect themselves from this threat.

Poor defenseless moss. :)

[brownbat]

I don't think anyone was talking about a garden variety:

http://en.wikipedia.org/wiki/Extremophile

Some organisms can already handle the radiation: http://en.wikipedia.org/wiki/Tardigrade