APG II (2003)
The second paper published by the APG presents an update to the original classification of 1998. The authors say that changes have been proposed only when there is "substantial new evidence" which supports them.
The proposed classification continues the tradition of seeking broad circumscriptions of taxa, for example trying to place small families containing only one genus in a larger group. The authors say that they have generally accepted the views of specialsts, although noting that specialists "nearly always favour splitting of groups" regarded as too varied in their morphology.
APG II continues and indeed extends the use of alternative 'bracketed' taxa allowing the choice of either a large family or a number of smaller ones. For example, the large Asparagaceae family includes 7 'bracketed' families which can either be considered as part of the Asparagaceae or as separate families.
Some of the main changes in APG II are:
- New orders are proposed, particularly to accommodate the 'basal clades' left as families in the first system.
- Many of the previously unplaced families are now located within the system.
- Several major families are re-structured.
In 2007, a paper was published giving a linear ordering of the families in APG II, suitable for ordering herbarium specimens, for example.
Read more about this topic: Angiosperm Phylogeny Group