FRUTICOSE LICHENS ​

STUDY OF EXTERNAL FEATURES OF THALLUS (FRUTICOSE LICHENS)

• These appear shrubby with cylindrical, flat or ribbon-like body.
• It is upright, generally branched and pendulous.
• It remains attached to the substratum by rhizoidlike structures forming a disc.
• The common examples include Usnea, Alectonia, Cladonia, etc.

STUDY OF INTERNAL STRUCTURE​ OF THALLUS (FRUTICOSE LICHENS)

• The transverse section appears almost circular.
• The internal structure shows four distinct regions, outermost cortex, the algal zone, medulla and the centrally located chondroid axis.
• Thallus structure is radially symmetrical.
• The cortex is made of closely packed and interwoven fungal hyphae. Intercellular spaces are absent.
• The algal zone consists of cell of unicellular green alga, Protococcus.
• Medulla follows the algal zone. It. consists of algal cells loosely mixed with fungal hyphae scattered in different directions.
• The central chondroid axis is made of longitudinally arranged, compact, thick walled and closely grouped fungal hyphae.

STUDY OF VEGETATIVE STRUCTURES OF FRUTICOSE LICHENS ​

• Vegetative propagation takes place by fragmentation, isidia and soredia.
• Fragmentation is the commonest of all the methods.
• Isidia develop as outgrowths of thallus. These develop into new lichen thalli after separating from the parent thallus.
• Soredia are bud-like outgrowths developing either from the entire surface or in localised patches called soredia.
• Soredia are developed in the gonidial layer.
• A soredium consists of a few algal cells surrounded by hyphae.
• Soredia get detached from the thallus and are carried away by the wind. Germination occurs on suitable substratum.