SYNOPTIC DESCRIPTION OF THE LICHENS
| LICHENS ARE CHIMERICAL ENTITIES AND, THEREFORE, HAVE NO NATURAL LINES OF DESCENT |
LICHENS LINKS
| The following description comes from Margulis and Schwartz (1988), Hale (1979), Ahmadjian (1967), and Nash (1996). |
I. SYNONYMS: lichens
II. NUMBERS: >18,000 species.
III. PHYLUM CHARACTERISTICS:
- A. ASEXUAL REPRODUCTION:The lichen can reproduce itself by the production of diaspores (text with tooltip) Any propagule, sexual or asexual. , lichenized structures in which the algal and fungal units function together as subunits of the lichen thallus; diaspores may be fragments of the thallus or specialized structures such as soredia (text with tooltip) Round or scale-like body on thallus of some lichens, which contains alga and fungal hyphae, by which lichen is propogated. and isidia (text with tooltip) Coral-like soredia on surface of some lichens. .
- B. SEXUAL REPRODUCTION:Sexual reproduction typically occurs only in the mycobiont (text with tooltip) The fungal component of a lichen. by ascocarps (text with tooltip) Mature fruiting body of ascomycetes; contain asci. or basidiocarps (text with tooltip) Fruiting body of a basidiomycete which bears spores on specialized cells. .
- C. VEGETATIVE HYPHAE:The lichen thallus is a primarily composed of the mycobiont which grows as a typical
mycelium
(text with tooltip)
A mycelium (mycelia, pl.) is a mass of hyphae or fungus-like filaments.
until it incorporates a particular phycobiont (usually Trebouxia) into the thallus. The resulting chimera is different from both the mycobiont and phycobiont individually. Since lichens have a photosynthetic component, they can grow on barren areas such as rock outcrops. They are also common on bark and soil. They usually form one of four thallus types:
- 1. FOLIOSE LICHENS (text with tooltip) Leaf-like – The thallus is flattened and leaf-like, with the upper and lower surfaces differing in color or surface features.
- 2. FRUTICOSE LICHENS (text with tooltip) Shrub-like – In fruiticose lichens the branches of the thallus are round in cross section, with few differences between top and bottom. They may be bushy, hairy, or strap-shaped.
- 3. CRUSTOSE LICHENS (text with tooltip) Crust-like thallus; stretched over and firmly fixed to substrate. – The thallus of crustose lichens is appressed to the surface of the substrate, and is sometimes in the substrate, in which case the outer margin is delimited by a dark line or color difference. Some small foliose lichens can be confused with crustose species. Crustose lichens are common on rocks and tree bark.
- 4. SQUAMULOSE LICHENS (text with tooltip) Scaly – These lichens are characterized by the squamules, small lobe-like structures which lack a lower cortex.
- See Bold et al. (1987) for structures of different thallus types.
- D. CELL WALLS: Usually chitin and glucan (text with tooltip) A group of polysaccharide sugars. from the mycobiont and cellulose from the phycobiont.
- E. ECOLOGY: They are found in almost all terrestrial habitats from exposed rock to mud and from arctic to tropical latitudes.
| LITERATURE CITED Ahmadjian, V. 1967. The Lichen Symbiosis. Blaisdell Publishing Co. Waltham, Mass. 152 p. Hale, M. E. 1979. How to Know the Lichens. 2nd ed. Wm.C. Brown Publishers. Dubuque, IA. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York. Nash, T. H., III, ed. 1996. Lichen Biology. Cambridge University Press. New York. 303 pp. |
