The fact for today:
Lichens may be the evolutionary link for the transition of plants from water to land.
What's a lichen, you ask? Simply, a lichen is not a single organism- it is two organisms that interact in a symbiotic way- in other words, they help each other. The organisms: fungi (think mushrooms) and algae (think green stuff in the water).
Fungi are interesting in that they breakdown their food before ingesting it. Humans inject our food, and then break it down, but fungii breakdown rocks and other materials in their local environment and then absorb it- this is how they eat. Algae, just like plants, make energy from sunlight.
So, the algae make energy for the fungi, and the fungi breakdown minerals from rocks for the algae. Together, they're called lichens. They are still around today, and are some of the oldest known organisms on the planet.
Pretty cool eh?