Some species of fungi will only grow to reproducing if they are colonised by a green algae or a cyanobacteria. The ‘guest’ species is surrounded by the host fungi, which provide it with a good environment for photosynthesis.

(The guests can live without the fungi host, but the fungi can’t live without the guest.)

What’s really interesting is that some of the fungi can live with more than one variety of guest - and will grow into different body shapes depending which one they absorb.

We call these symbiotic systems ‘Lichens’.