Lichens- Forms of lichens, Internal morphology, Reproduction, Economic importance.

Lichens:

• The symbiotic assosiation between fungi and algae resulting in a plant body is called lichens.

• Plant body of lichen thallus is irregular and made up of algal component i.e. phycobiont and fungal component i,e. Mycobiont.

Differnt forms of lichens:

1. Crustose lichen:

    These are flat, thin, crust like thallus appeared partly or completely embedded into the substratum.  Ex. Rhizocarpa graphis.


2. Foliase lichens:

   These are flat, leaf like lobed thallus attach to the substratum with the help of rhizoids.  Ex. Permeria.


3. Fruticose lichens:

    These are brush like hanging cylindrical or spherical shape. Attached to substratum with the help of basal mucilage disk.
     Ex. Cladonia.


Internal morphology of lichen thallus:

   It shows mainly four zones. They are:
           1. Upper cortical zone
           2. Algal zone
           3. Medullary zone
           4. Lower cortical zone

1. Upper cortical zone:
   
      It is a protective layer where certical fungal hyphae are attached.

2. Algal zone:

      It contains algal cells enveloped bupy fungal hyphae.

3. Medullary zone:

     It consist of loose, inter removal hyphae which forms parenchymatous cells.

3. Lower cortical zone:-

  Compactly arranged hyphae are developed and consist of Rhizine which helps to attach to attach to the substratum.


Reproduction in lichens:

1. Vegetative reproduction:

    Vegetative reproduction takes place by following methods.
         ● Fragmentation
         ● Diaspores

    ☆ Fragmentation:
   
         The thallus of lichen broken down into fragments and when falls on a suitable substratum it develops into a new thallus.

     ☆ Diaspores:

      It is of three types.

• Isidiae/Isidium: It is a small outgrowth from upper surface of lichen which consist of algal cells and fungal hyphae, when it gets seperate from mother cell it develops into a new lichen.

• Soridiae/Soridium: It produces a spores called sorodia which gets dispersed and reach to suitable su stratum and develops into a new thallus.

• Cephalodeae/Cephalodium: The algal and fungal cells accumulate and forms swelling, which gets disposed and reach to substratum and develops a new thallus.

2. Asexual reproduction:

•     Asexual reproduction takes place only in fungal components.
•   Lichen produces a flask shaped structure called pycnidium which has opening called as ostiole.    Some fungal hyphae from the walls of pycnidium develops  pycnidiophores, these are the spores which gets dispersed and develops into a new lichen body.

3. Sexual reproduction:

•     Sexual reproduction is takes place exclusively in fungal components. Ascolichens produces Ascospores and Basidiolichens produces Basidiospores.

• In Ascolichens the female sex organ is called Carpagonia and male sex organ is known as Spermagonia.

• In Basidiolichens lower cortex produces fertile hyphae which further develops and forms basidiospores.

Economic importance of lichens:

• The lichens helps in disintegration of rocks into soil particles chemically or mechanically and act as pioneers of vegetation.

As food:

• In India Permelia used as curry leaf. In Japan, Umbillicaria Ascolents is used as vegetable. Lecanaro is used as food by Africans during drought condition.

As medicine:

• Lichens posses antibiotic properties.
• Exythrin obtained from Rocella Montagnei used in heart diseases.
• Clodonia is used to cure cough, cold etc.
• Xanthoria used to cure Jaundice.

Lichens as dyes:

• Orchill obtained from Rocella Tictoria used in dying wooden and silk fabrics.
• Brown dye obtained from permelia.
• Litmus solution used in laboratories are obtained from Rocella Montagnei.

Lichens as Pollution indicator:

• It does not grow in polluted water bodies. Itcan measure the leval of sulphur di oxide and several toxic metals like Lead, Nickel, Mercury, Zinc, etc.