Highgate resident (yellow lichen on yew tree)

Lichens are symbiotic organisms, where fungi and algae work together to exploit sunlight and create glorious stains on trees and tombs. These are foliose lichens, with small, flat leaf-like structures. The marked contrast of yellow lichen on dark bark is quite common in cemeteries. They are at their best when they catch the setting sun light.

Purple bacteria II

Purple bacteria or purple photosynthetic bacteria are pigmented by bacteriochlorophyll and carotenoids, giving them a colourful range of purples, pinks and oranges. They photosynthesize without producing oxygen as a by-product. This type of bacteria are proteobacteria which are phototrophic (produce their own food via photosynthesis).

One type, purple sulphur bacteria, deposit elemental sulphur –brimstone – instead. Others oxidise iron to form rusty banded iron formations.

Cyanobacteria at work

Also known as blue-green algae, cyanobacteria are arguably the most successful group of microorganisms alive today. They are genetically very diverse, and able to live almost anywhere, even in extreme conditions. The nitrogen-fixing cells are bright little suns here, in a stormy sea.