iGrow for Craftbukkit allows for the use of "recipes" to grow / create blocks and plants on a CraftBukkit server based on the time and distance set in the configuration. This plugin allows for moss grow on cobblestone (among other things,) just like grass grows on dirt.
key/value recipe lines (eg. old:AIR,new:GLOWSTONE,needs:LEAVES,chance:30/100,world:myworld,near:false)
This allows lines to be read in any order, easily verify recipes, default values for world & near so doesn't matter if these are left out.