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2a.

It has been said, that there are as many concepts of the basic categories of plant classification as that a distinct designation of each of these is not necessary. That is a truth with considerable modifications, although it may fit too much to the application of the descriptive method when used for little known taxa. Although Linnaeus never directly defined his categories, it is implicit in his work that he was thinking of a certain degree of relationship and phylogeny at the levels beyond the genus, and such an idea has been increasingly basic to most taxonomic work by later generations. But when the knowledge of a taxon has reached the level of the comparative method based on the theory of evolution, the distinct designations of the basic categories become impractical. Therefore, systematic taxonomists applying the empirical methods as additional to morphology for the exact biological classification of thoroughly known taxa may accept the family in its traditional sense as a collection of genera which are likely, as far as morphological indicators may go, to have evolved from a common ancestor, although frequently this cannot be proven by aid of any cytological indicators. For the other categories, or the genera, species, subspecies, varieties, however, the biological concept (biological or evolutionary concept) is (biologically) decisive. According to that concept, a taxon at the genus level, biological or evolutionary, biological or evolutionary modification of the Linnaean concept is modified in such a way that a taxon at these levels is defined biologically or cytogenetically but identified morphologically, primarily by aid of characters of flowers, fruits or flowering branches as advocated by Linnaeus (1753), since these attributes are less affected by planetary influences than the more vegetative characteristics. The biological approach suggests that natural groups are separated by restrictions or barriers to crossability tending towards total incompatibility (Gleiser, Line 1975a, 1975b). Such clusters of related species should, as far as possible, demonstrate morphological, cytological, or other evidence of linear branching evolution within the group, i.e., they have common phylogenetic restricted reproductive isolation without reticulation to earlier stages of relationship, as well as restricted crossability and