Since the classification that led to this tree is based on evolutionary principles and evolution involves changes between ancestors and descendents node 4 indicates a species ancestral to Q and O. In that case the trait was lost by 2 (or some descendents of 2), by G and by U - in other words the trait was lost at least three times. Though this fungal-based taxonomy of lichens has been accepted for over a century, for much of that time lichenized and non-lichenized fungi have been studied largely as separate subjects. Classification of Lichens: The systematic position of lichens is a controversial matter because it is a combination of two different members of two different groups. The yellow area in the small tree to the right shows where the large tree fits into the tree of all ascomycetes. Lichens are classified by the fungal partner, so all lichens belong to the fungal kingdom. About 64,000 ascomycete species are known, of which about 18,000 are lichenized. THE CLASSIFICATION OF LICHENS THE CLASSIFICATION OF LICHENS WATSON, W. 1929-03-01 00:00:00 XXVIII, No. Genus, family, order, class, phylum and kingdom are also examples of taxonomic ranks. For a start, there are both ascomycete and basidiomycete lichenized fungi, albeit very few of the latter. It is worth repeating some numbers given earlier. 'Species' is an example of a taxonomic rank while Pannaria sphinctrina, a particular species, is an example of a taxon. The fruticose lichens constitute larger and attractive growths standing out from the branches of trees, foliage and rocks. Lichens are found abundantly growing in various places like on rocks, walls, gravestones, on roofs, tree barks, soil, etc. Required fields are marked *. The Dothideomycetes is the one class within which lichenization has occurred several times independently but the evidence is insufficient to determine whether the immediate ancestor of the Dothideomycetes was lichenized or not - hence the question mark. Someone else may argue that rather than three genera there should be just two, with the first two of the above three groups defined as the one genus. Hence the group (3,4,Q,O,D), of which only the last three are extant today, is an example of a monophyletic group. Intermediate types include leprose and squamulose lichen, among others. An organism's genome is its hereditary information, stored as DNA. In either case the current distribution of lichenized and non-lichenized taxa calls for one or more losses or gains of lichenization to account for the current mix of lichenized and non-lichenized taxa. Some of those features had been used in ascomycete classification since the late 1800s but electron microscope studies gave more detailed structural information. A very large proportion of lichens belong to just one class and, on current evidence, that class arose from one gain of lichenization. In such analyses one looks at equivalent sections from the genomes of different species and the results are presented as sequences of letters, indicating how the four basic DNA components (adenine, cytosine, guanine, thymine) are arranged. The division of organisms into species, genera and so on has always been a way of summarizing that diversity. In this hierarchical ordering of living organisms, the total number of species is greater than the number of genera, which in turn is greater than the number of families and so on. The Dothideomycetes is the largest class within the ascomycetes and contains about 19,000 species - but only a small number of lichenized species. It would be natural to ask how the situation described by these quotations could be tolerated for so long. SINCE the publication in 1894 of the first part of this Mono-graph'many advances have been made in the study of lichenology, and consequently the classification used by Crombie has been ' "A Monograph of British Lichens," Part I, hy the Rev.