CRUSTOSE LICHENS

STUDY OF EXTERNAL FEATURES OF CRUSTOSE LICHENS

Comments :-

• The crustose lichens are hard, granular crusts on rocks and bark of the trees.
• These adhere very closely and firmly to the substratum.
• The thalli are partially or completely embedded in the substratum. 
• These lichens are generally ash-coloured. However, the colours may vary.
• The surface of the thallus is generally divided into polygonal areas called areolae.
• Some of the commonest examples include Lecidea, Graphis, Lecanora.

STUDY OF INTERNAL STRUCTURE​ OF CRUSTOSE LICHENS

Comments :-

• The thallus is poorly differentiated. 
• The tissues forming the thallus are arranged more of less in strata, one above the other. 
• The upper cortex is made of rudimentary or sometimes highly developed hyphal layer.
• Algal layer lies just beneath this layer. The layer shows agal filaments and the fungal hyphae in close association. 
• Much below the algal layer lies the medulla composed of loose tissue of branching hyphae. 
• The lower cortex lies next to medulla. It may be well developed or entirely absent.

REFERENCES

• https://en.wikipedia.org/wiki/Crustose_lichen
• https://depositphotos.com/stock-photos/crustose-lichens.html