Angiosperm Phylogeny Group - APG I (1998)

APG I (1998)

The initial 1998 paper by the APG made angiosperms the first large group of organisms to be systematically re-classified primarily on the basis of genetic characteristics. The paper explains the authors' view that there is a need for a classification system for angiosperms at the level of families, orders and above, but that existing classifications are "outdated". The main reason why existing systems are rejected is because they are not phylogenetic, i.e. are not based on strictly monophyletic groups (i.e. groups which consist of all descendants of a common ancestor). An ordinal classification of flowering plant families is proposed as a "reference tool of broad utility". The broad approach adopted to defining the limits of orders resulted in the recognition of 40 orders, compared to, for example, 232 in Takhtajan's 1997 classification.

Other features of the proposed classification include:

• Formal, scientific names are not used above the level of order, named clades being used instead. Thus eudicots and monocots are not given a formal rank on the grounds that "it is not yet clear at which level they should be recognized".
• A substantial number of taxa whose classification had traditionally been uncertain are given places, although there still remain 25 families of "uncertain position".
• Alternative classifications are provided for some groups, in which a number of families can either be regarded as separate or can be merged into a single larger family. For example, the Fumariaceae can either be treated as a separate family or as part of Papaveraceae.

A major outcome of the classification is the disappearance of the traditional division of the flowering plants into two groups, monocots and dicots. The monocots are recognized as a clade, but the dicots are not, with a number of former dicots being placed in separate groups basal to both monocots and the remaining dicots, the eudicots or 'true dicots'.