The Protoctista Kingdom includes one celled and simple multicelled protozoa, slime moulds and algae.

Protozoans

These are minute one celled organisms and include the simplest ‘animals’ such as amoeba, sporozoans and flagellates. Being unicellular (made up of only one cell), you will need a microscope to see them. They are present in large numbers yet have been little studied in caves. Some probably live in the caves and others are washed in.

Slime moulds – these strange things are amoeba like during their feeding stage, and produce brightly coloured fungi when mature. They have characteristics of both plants and animals.

ALGAE

Some free living algae are found deep in caves and some have an absence of chlorophyll. These algae use non-photosynthetic metabolic pathways to survive without light. Many species exist in the soil. Organic matter in water can be used as a substitute for photosynthesis by algae.
Some of these microrganisms (algae, bacteria and small fungi) are eaten by cave insects, others may live inside the insect digestive system – both enabling the cave insect to survive in an environment where food is scarce.

Kent's Cavern. Patches of green algae can be seen growing on the flowstone.

HIGHER PLANTS

Higher plants (higher refers to their more advanced structure rather than height) need sunlight and are only found above ground, consequently they are limited to the threshold zone of caves, although roots can be seen deeper into the cave if the passage lies sufficiently close to the surface. They can be found growing around the lights of show caves.

Roots in Corbridge cavern