Algae-like growths: Dark green or blackish jelly-like growths that often appear in damper, cooler weather over the surface of the lawn, making it slippery are caused by a cyanobacteria called Nostoc. These are sometimes referred to as gelatinous algae or blue-green algae but are technically classified under bacteria, not algae.
Lichens: In turf the most common lichen is Peltigera spp. (dog lichen); it is brown or grey and formed of flat structures that grow horizontally in the turf.
Liverworts: Liverworts on lawns usually have a green, flattened body and no leaves. A common example is Marchantia, which is often topped with umbrella-like sexual organs.
Slime moulds: Wet weather in autumn or spring can also lead to the growth of slime moulds. These growths, which may be white, yellowish or orange, produce small grey fruiting bodies that subsequently release masses of purplish-brown spores. The growths are purely superficial and do not harm the grass but they are unsightly.