Arrange the following species in general trend of succession on a rock starting from crustose-lichens stage to shrub stage.
A. Parmelia
B. Polytrichum
C. Rhizocarpon
D. Festuca
E. Phytocarpus
Choose the correct answer from the options given below:

Correct option is C

Introduction

Primary succession on bare rock (a lithosere or xerarch succession) proceeds through a defined sequence of pioneer and later communities, each modifying the substrate to make it habitable for the next.

It begins with crustose lichens on lifeless rock and advances through mosses, herbs, and shrubs toward an eventual forest climax.

Information Booster

The correct successional order from the crustose-lichen stage to the shrub stage is — Rhizocarpon → Parmelia → Polytrichum → Festuca → Phytocarpus.

Each stage progressively deepens and enriches the soil, illustrating the ecological principle of facilitation, in which pioneer organisms alter the environment to favour their successors.
C. Rhizocarpon is the pioneer crustose lichen and the true starting point of rock succession. Crustose lichens adhere tightly to the bare rock surface, secreting organic acids that chemically weather the mineral substrate.

They tolerate extreme desiccation, temperature swings, and nutrient scarcity, and their slow breakdown of rock, combined with trapped dust, initiates the very first thin layer of soil.
A. Parmelia represents the foliose (leafy) lichen stage that follows. Foliose lichens are only loosely attached to the substrate and have a larger, leaf-like thallus that traps far more windblown debris, organic matter, and moisture than crustose forms.

This accelerates the accumulation of a rudimentary soil layer and improves water retention.
B. Polytrichum is a moss that colonises once a rudimentary soil and moisture-holding layer has formed. Mosses form dense mats that hold water, trap sediment, and add substantial organic matter as they grow and die, thickening the soil and preparing it for the establishment of rooted vascular plants.

D. Festuca, a grass, marks the herbaceous stage. By this point the soil is deep enough to support rooted herbs and grasses whose fibrous root systems bind and stabilise the substrate, draw up nutrients, and contribute significant organic material, further transforming the site into a true soil.

E. Phytocarpus represents the shrub stage, the woody community that establishes on the now deeper and more fertile soil. Shrubs shade out low-growing herbs, develop extensive root systems, and drive the succession onward toward the climax woodland community.