I get strange weeds, mosses all the time on cork. One I collected, off a cork tube, I have begun propagating. Its great. Bright green, fluffy, and spreads really fast. Ive had monocots grow for 2 weeks and die. I have had clover and liverworts pop up. Its hard to tell exactly bc the frogs trample and spread things around. Who knows where. I get all kinds of things that grow out of the soil from other plants I buy.