ABSTRACT
In a phylogenetic system, the various categories could be defined in relation to the various degrees of remoteness of this common ancestral species, measured in years or in generations; it is, in fact, the only type of classification which offers the possibility of really objective criteria for supra-specific categories. The concept of a 'mode of life' to which an organism is 'adapted' structurally and physiologically, is undoubtedly more difficult for us at present to apply to plants than to animals. Animals live faster, their behaviour and reactions can be directly observed by human beings, the relationship between particular features of behaviour and specific structural characters is often self-evident. In the vertebrate groups, knowledge of phylogeny is based on a relatively good fossil record. Fossils, as the most direct source of information about organisms of the past, are potentially the most valuable of all evidences for evolutionary ancestry.
