Distribution is cosmopolitan. As fungi generally lack hard parts, they are rarely found as fossils, but possible thread like representatives have been found in Precambrian rocks. Classification of Fungi Lichen: A type of composite organism which consists of a fungus the mycobiont and an alga the phycobiont living in symbiotic association.
A lichen thallus may be crust like crustose , scaly or leafy foliose , or shrubby fruticose , according to the species. Lichen are classified on the basis of fungal partner; most belong to the Ascomycotina.
Specialised asexual reproductive structures may be produced. Many lichens are extremely sensitive to atmospheric pollution and have been used as pollution indicators.
Fungi are multicellular organisms that are heterotrophic in nature. Heterotrophs are those organisms who cannot make their own food. Fungi are eukaryotic in nature, which means they have cell organelles like a nucleus. Fungi are essential to the smooth functioning of the natural ecosystem.
Mycology is the term for the study of fungi. Fungi can reproduce by sexual and asexual modes of reproduction. Yeast is single-celled fungi.
Fungi also alternate between single and multicellular organisms depending upon the life cycle stage. Multicellular fungi have hyphae, which are tubular filament-like structures. The cell walls of fungi are made up of chitin, which is a hard substance commonly found in the exoskeletons of insects. Fungi use the filament-like outgrowths to obtain food.
Fungi can thrive in most environmental conditions and can obtain its food even from dead and decaying matter. This is the reason why fungi are essential to the natural ecosystem. Fungi clean up the dead and decaying matter by breaking it down.
The site navigation utilizes arrow, enter, escape, and space bar key commands. Up and Down arrows will open main level menus and toggle through sub tier links. Enter and space open menus and escape closes them as well. Tab will move on to the next part of the site rather than go through menu items.
Is this a lichen or a moss growing on a tree trunk? Photo by Chad Merda. Most of us assume the fuzzy green stuff we see growing on tree trunks or rocks on the forest floor is moss.
And while moss is a likely suspect, it could also be a lichen. So what's the difference between a moss and a lichen? Telling them apart can be difficult. It certainly doesn't help that some lichens have common names that include the word "moss," like reindeer moss, which is actually a lichen, according to 21st Century Parks.
Just in case you're interested, such a lichen is called placodioid or placoid and Placopsis perrugosa is an example.
In most cases a species will always have the same gross morphology but a number of species are known to show some plasticity. This box gives one example. Usually Siphula coriacea is characterised by erect, bluish grey lobes, shown here. The species is known from mainland Australia and New Zealand, in heathlands and grasslands.
In moister, sheltered areas the lobes may be over a centimetre in length but in the drier rangelands of inland Australia the lobes are markedly shorter, often only a few millimetres in length.
An unusual form has been found in Idalia National Park, western Queensland. The thalli consist of more or less circular disks, rather than of erect lobes. The discoid thalli, shown here , are from two to eight millimetres in diameter and, though different in gross morphology, match the usual forms of this species in both chemistry and micro-morphology.
Typical forms of Siphula coriacea were found elsewhere in the same general area. All of these expressions may be called usefully imprecise descriptive terms. They are useful in the same way that expressions such as shrub and tree are useful when talking about plants. They are imprecise in that sometimes it may be difficult to place a particular specimen in a particular growth form 'pigeon-hole'. Similarly, occasionally you may wonder which of shrub or tree is the better term to describe a particular plant.
What of the byssoid lichens? Logically you could argue that a byssoid growth form is three dimensional as is a clump of cotton wool and so a byssoid lichen is really just a very delicate fruticose lichen. Some lichenologists consider squamulose and placodioid forms as simply variants of crustose. As you can see there is a variety of terms more than listed above and some debate over the boundaries between them.
It is useful to be aware of these issues, since different books or websites may use some terms in slightly different senses, but there is no point in getting bogged down in terminology. For most purposes it is enough to be comfortable with the terms crustose, foliose, fruticose and squamulose as defined above.
In general a particular species will show the same growth form, no matter where it grows. Occasionally, for some reason perhaps genetic, perhaps environmental , a species that is usually, say, crustose might grow in a fruticose form. Such occasional, but dramatic, differences in growth form in the one species are well-known to many gardeners. A plant species that usually grows as a tree may be found growing in, say, a prostrate form.
Often such plant variants are highly valued horticulturally and propagated vegetatively to preserve the variant form and sold as cultivars of the species in question. You may come across the terms macro-lichen and micro-lichen. These are two more examples of usefully imprecise terms. Roughly speaking a macro-lichen is one that is foliose or fruticose and the rest are micro-lichens. Note that this has nothing to do with size, despite the impression given by the prefixes macro and micro.
A species that typically grows as a foliose form to say a centimetre diameter would be a macro-lichen whereas a crustose species that typically grows to over 10 centimetres in diameter would be a micro-lichen. In the Usnea photograph above you can see a prominent smooth, circular disk. If you look at this photograph of the foliose lichen Paraparmelia lithophiloides , you'll see that much of it is grey to blackish but there are also a number of brown disks.
In those disks, called apothecia , the fungal partner produces spores and the apothecia are part of the fungal reproduction process. The bulk of each lichen that is, the branches in Usnea and the grey to blackish areas in Paraparmelia lithophiloides is called the thallus and is known as the vegetative part of the lichen. The thallus is composed of fungal and photobiont cells, so well united as to give the impression that you are looking at just one organism.
In most lichens it is the thallus that is dominant and when talking about lichen growth forms it is always the thallus that is being described. There'll be more about apothecia and other spore-producing structures a little further on. For the moment, let's concentrate on the thallus of Paraparmelia lithophiloides. This is a foliose lichen so it is more-or-less flat in form so let's see what the thallus looks like in cross-section. The upper surface is composed of compacted hyphae and this band of compacted hyphae is called a cortex.
Below the cortex is a band of photobiont cells and below that is the medulla , an area of loosely arranged hyphae. It is in the medulla that the fungus stores the nutrients it has "harvested" from the photobiont. Below the medulla is the lower surface of the thallus, composed of compacted hyphae and constituting another cortex. From the lower cortex root-like bundles of hyphae, called rhizines , anchor the thallus to the substrate.
You find this sort of structure in many foliose lichens. The thallus of Paraparmelia lithophiloides has an upper cortex and a lower cortex and that is the norm in foliose lichens.
0コメント