Coralline algae are red algae in the order Corallinales, characterized by a thallus containing calcareous deposits within its cell walls, giving it hardness. The colors of these algae are typically some hue of pink, or another shade of red, but some species can be purple, yellow, blue, white, or gray-green. Typically, these algae grow in a crustose manner ; in the intertidal zone of rocky shorelines, and within coral reefs, these algae appear as an abundance of colorful patches on rock surfaces. Unattached specimens may form relatively smooth compact balls, and use underwater photosynthesis to get food or forming warty to fruticose thalli.