Question

The early settlers on a barren area (rock) are:
A.Ferns
B.Mosses
C.Lichens
D.Diatoms

Answer 1

They are an example of symbiotic organisms. Lithosere is the succession of bare rock such as that exposed on the melting of glaciers or by the formation of new landmass by volcanic eruptions.

Complete step by step answer:
The lichens stage is the first stage in the case of a lithosere. Bare rock is first invaded by the crustose lichens, for example, graphis, Rhizocarpon, etc.
They corrode the rock at places by their hydrolytic enzymes causing foliose lichen (for example, Parmelia, Dermatocarpon, etc.) to invade and eliminate the crustose lichens. It also creates conditions suitable for invasion by mosses
In the tropics, the blue green algae are the pioneers instead of lichens in lithosere.

Hence option C is correct.

Additional Information:
Xerosere is a plant succession that is limited by the availability of water. It includes the different stages in a xerarch succession. The xerarch succession of ecological communities originates in extremely dry/ arid conditions such as sand deserts, sand dunes, salt deserts, rock deserts, etc.
Hydrosere is the plant succession that occurs in areas of fresh water. Over time, the area of the open freshwater will naturally dry out and will ultimately become a woodland. During this change to woodland, a range of different land terrains/ types. This includes the bare bottom stage, submerged vegetation stage, emerged vegetation stage, temporary pond stage, climax/ forest/ woodland stage.

Note:
Lichens are symbiotic organisms wherein a fungus and a moss coexist for the benefit of each other. It is the most efficient of air quality in an area, it is less dense and less white in areas of high air pollution. The moss is photosynthetic and provides food to the fungus, the fungus provides support and protection to the moss.