Moss

Moss is a grass-like plant plant that grows on stone blocks. It comes in five colors, and one color can be found throughout each third of a given map (three colors per world), either randomly on cave surfaces or in "moss chambers" with a matching mossy stone wall. Moss sprouts fuzz that can be cut like grass weeds, and mossy stone requires one more hit to break than clean stone, but otherwise moss does nothing. Moss will be destroyed if the stone block it is on becomes ebonstone, crimstone, or pearlstone.

Spread
Moss slowly spreads across exposed stone blocks. Although there are no moss seeds, a player can grow extra moss by building "bridges" of stone for existing moss to grow across. Moss cannot grow above zero depth.