BIO 102 DIVERSITY OF LICHEN

BIO 104 PLANT DIVERSITY

LECTURE NOTE BY Dr. Bup Oyesiku

DEPT Plant science and Applied zoology, OOU

MODIFIED BY Admin

INTRODUCTION

LICHENS are mostly land dwelling plants (terrestrial). A LICHEN is an alliance between two unrelated organisms, a fungi MYCOBIONT (mostly Ascomycota (90%) and Basidiomycota) and a photosynthetic PHOTOBIONT partner (cyanobacteria and algae) e.g Nostoc . It is a kind of Controlled parasitism rather than commensalism. The study of Lichen is called LICHENOLOGY. They occupy inhospitable habitats and they share similar reproductive structures with fungi. The minor partners are sandwiched in between the major partners. It is important to note that both the cyanobacteria and algal partners can live on their own but the modified Mycobiont fungal partner cannot survive without this association. Lichens have a thalloid body shape.

REPRODUCTION

Reproduction can be  in the following forms:

1) VEGETATIVE: lichens reproduce by vegetative propagules called ISIDIA AND SOREDIA, which are dispersed by wind and animals.

2) ASEXUAL: Only the fungal partner has been observed to produce asexual propagules, in a structure called PYCNIDIA. It resembles the PERITHECIUM in Ascolichen.

3) SEXUAL: Only fungal partners are involved. The most commonly used sexual structure is called APOTHECIA. It is circular and cup shaped.

CLASSIFICATION

Basically lichen are divide into two: Ascolichen and Basidiolichen. Ascolichen form about 95% of the lichen. We're concentrating on ascolichen. Ascolichen are divided into three, based on thallus forms.

1) CRUSTOSE LICHEN: They are the simplest form of lichen. They resemble bread crumbs. Attached strongly to substrate, and growth pattern is radial. Thallus edge is flat. Lichen is unlobed. Thallus hard to remove without damaging substrate.

2) FOLLIOSE (leafy) LICHEN: They are leaf like. Thallus  is  profusely lobed, and raised above the substrate. Attachment is by root like RHIZINES. Growth takes place at y margins of lobes. Dorsal (up) and Ventral ( down ) layers colours are different.

3) FRUTICOSE LICHEN: Shrub like lichen. They are the umbilicate lichen. They are attached to substrate by means of HOLD FAST. Thallus is circular in cross section. They have the tastes growth rate of all lichen.

Another classification is based on lichen habitats.

Bark- Corticolous lichen Decaying wood- Lignicolous lichen Leaf- Follicolous lichen Moss- Muscicolous Rock- Saxicolous Soil- Terricolous

Lichen Habitats range from tropical to polar regions. Habitats include rocks, tree barks, leaves, on the soil not beneath, tundra and desert sands, few in water.

ECOLOGY AND ECONOMIC IMPORTANCE

All lichens grow slowly except fruticose lichen. Growth rate is 0.5 - 5.0 mm per year,with fruticose reaching up to 20mm per year. The fungal partner protects against desiccation and harsh conditions, while the photosynthetic partner produces food. Nitrates from decomposing lichens help to fertilize soil. Lichens cause bio deterioration especially of artworks an large monuments. It is important to note that Lichens are sensitive to environmental pollution, and are used as effective bio indicators of environmental pollution. Physically, lichens are capable of causing fragmentation of rocks and hence help in soil formation. Human consumption is not common,aslichen are very bitter. Only the genus Umbilicaria has be reported to have been consumed. Some lichens have antibiotic properties. Some lichens are used in the preparation of laxatives , tonics, and deodorants.