The most effective method is a cold dragon (lv 10 left) and a plant dragon (lv 10 right).
The lichen dragon unlocks at user level 9. It takes 6 hours to breed, and another 6 hours to hatch. It gives 6,000 experience points when hatched. It can be purchased in the market for 100 gems. The egg is light blue with green vertical wavy stripes.
Some other breeding methods are (listed left to right and level 10):
I got mine with a magnetic dragon and a lichen dragon and got it while trying to get another apocalypse dragon.
Fire Dragon and Lichen Dragon
It will make a lichen dragon
You don't breed a Kairos Dragon in DragonVale. You have to get parts to complete it.
A lichen, poison, bluefire, or frostfire dragon.
you breed a ice dragon with a mine dragon
You have to breed a plant and a fire dragon.
As of July 2012, there has not been a star dragon in DragonVale.
You would either get a Cactus dragon, a Storm dragon, a Lichen dragon, an Ash dragon, a Hail dragon, a Sun dragon, or a Moon dragon.
You have to breed a sun and moon dragon together
You have to breed a metal and a water dragon together.
You have to breed a plasma dragon with a salamander dragon.