This is a small, dark green lettuce-like algae when wet, which forms flaky coatings over rocks and boulders. Length 1cm.
It grows on rocks and stones in the splash zone, mostly frequented by seabirds which drop their faeces from which it gets its nitrates to flourish. A common and widespread species, but mainly seen in spring and early summer.
Photographs of Prasiola stipitata taken April 2013, Llandudno, Wales. © Pete Hillman 2013. Camera used Nikon Coolpix P500.