Lichens have been described as "dual organisms" because they are symbiotic associations between two (or sometimes more) entirely different types of microorganism -
a fungus (termed the mycobiont)
a green alga or a cyanobacterium (termed the photobiont).
There are many examples of symbiosis in nature, but lichens are unique because they look and behave quite differently from their component organisms. So, lichens are regarded as organisms in their own right and are given generic and species names. However, for taxonomic purposes the names are actually fungal names: lichens are regarded as a special group of fungi - the lichenised fungi.
There are an estimated 13,500 to 17,000 species of lichens, extending from the tropics to the polar regions. Some of them grow on the bark of temperate trees or as epiphytes on the leaves of trees in tropical rain forests. Others occupy some of the most inhospitable environments on earth, growing on cooled lava flows and bare rock surfaces, where they help in the process of soil formation, and on desert sands where they help to stabilise the surface and enrich it with nutrients (Cyanobacteria). Some other types of lichen grow abundantly on tundra soils, providing a vital winter food source for animals (including reindeer and caribou) in arctic and sub-arctic regions.Yet other lichens grow on or in the perennial leaves of some economically important tropical crop plants such as coffee, cacao and rubber, where they are regarded as parasites.
All these features make lichens interesting and significant in environmental terms. But lichens also pose challenging scientific problems - how do two or more microorganisms interact at the cellular, genetical and biochemical levels to produce a unique, hybrid organism?
The types of lichen
The "body" of a lichen is termed the thallus, and its general shape enables us to group lichens into four broad categories.
Foliose lichens have a flat, leaf-like structure .
Fruticose lichens have an erect or pendulous, bushy structure .
Squamulose lichens have a thallus consisting of minute, scale-like squamules .
Crustose lichens produce a flat crust on or beneath rock or tree surfaces .
2006-09-05 00:17:03
·
answer #1
·
answered by smalleyessharpviews 3
·
1⤊
0⤋
If your spelling is correct, the usual meaning for "'Licans" is short for Republicans.
If you mean Lycans, as in the movie "Underworld," then lycan is short for "lycanthrope" or "werewolf." You know, a man who changes into an abomination of half-wolf/half-man on the full moon.
2006-09-05 05:48:51
·
answer #2
·
answered by Leather M 3
·
0⤊
0⤋
do you mean lycans? i never heard of licans but lycans are werewolves
2006-09-05 05:45:50
·
answer #3
·
answered by ♥sandpaper kisses♥ >^..^< 4
·
0⤊
0⤋
I think you are asking about Lichens.
If yes, then lichens are symbiotic associations of Algae and fungi.
Lichens can tolerate extreme temperature, heat, light stress and mineral deficiency.
2006-09-05 06:06:24
·
answer #4
·
answered by Habib A 3
·
2⤊
0⤋
wolves
2006-09-05 05:40:07
·
answer #5
·
answered by Gersin 5
·
2⤊
0⤋