A cleaved sample of a crustose lichen growing on limestone. The image has been hand-coloured to reveal the different structures in the image, which was originally a grayscale scanning electron micrograph. The grey areas are limestone, the orange are fungal threads and the green shows algal cells. The fungal threads anchor the algae in place, close to the surface of the lichen to optimise their position for photosynthesis. Lichens are best thought of as miniature ecosystems, the overall structure and scaffolding produced by multiple fungal species and the interior housing algae or cyanobacteria, yeasts and other microorganisms in a mutualistic arrangement. Youlgrave, Derbyshire. February. False-coloured scanning electron micrograph, produced at the University of Derby. 0.14mm across in real life, x715 magnification when printed at 10cm across.