Genus concept

Many bacteria are rod-shaped and the term baciiius has been ioosely used to describe them. The genus concept of Bacillus, however, has been narrowed considerably with time Bacillus is now defined as Gram positive rod-iike, aerobic bacteria that form spores. 

To make this precise, we define a cut in a molecule to be the conceptual dissection of a covalent connectivity a cut of a covalent bond of formal order n is counted as being n cuts. In some molecules the formal order of certain covalent bonds is not an integer. In such cases one can either approximate the bond order by an integer, or use a fractional bond order consistently for counting the cuts the genus for such molecules may therefore be not an integer in the latter case. With these concepts, we can make the precise... 

One additional important concept to consider is that of peptide classification. If each sequence in peptide space is considered an individual species, then our clusters of green boxes are representative of a higher order of classification, the genus. With this concept in mind, Table 1 is an attempt to produce a generic classification of peptides. The number of individual species in each genus is, of course, variable and no doubt the future will see the evolution of new genera... 

The units one has to work with, the taxa from low to high, may be fixed, about the contents of these concepts a number of questions can be asked. Partly these questions are philosophical (does a species, a genus really exist in nature or only in the human mind ), partly they are quite practical (to which criteria must species, genera etc. answer ). Especially about the species concept there has been a lot of discussion and opinions did and do differ. For many a species is a unit that has to be morphologically recognizable with preferentially two constant differences with other species, for others the species is more or leas identical with the hybridization com-munity. Genet.ical "identity" of the components of a species is an important criterium and may lead some to forbid different chromosome numbers within one species. The battle about "biological and "taxonomical or less clear event linnean)" species started in the forties when herbarium taxonomists were confronted with students of... 

Hoef-Emden, K. (2007). Revision of the genus Cryptomonas (Cryptophyceae) II incongruences between the classical morphospecies concept and molecular phylogenyin smaller pyrenoid-less cells. Phycologia 46, 402-428. 

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