Abstract:

With the rise of plant molecular systematics, tremendous progress has been made in understanding phylogenetic relationships within angiosperms. With the basic phylogenetic framework of angiosperms established, a DNA phylogeny-based angiosperm classification system at the order and familial levels was proposed by the Angiosperm Phylogeny Group (APG) in 1998 and has been updated three times. In this paper, we summarize the major achievements of the APG system as follows: (1) testing the repeatability and predictability of the APG system for angiosperms; (2) resolving the systematic positions of some segregate taxa which were not placed based on morphological characters; (3) proving that it is not reasonable to first divide angiosperms based on cotyledon character; (4) demonstrating the importance of tricolpate/tricolporate pollen and derivatives for angiosperm classification; (5) finding that the centrifugal development of stamens in polyandrous groups have evolved independently many times and should not be used to delimit class or subclass of angiosperms; (6) supporting that most of the families delimited by broad morphological characters are natural; and (7) separating some families which are traditionally regarded as natural. We then point out potential problems that need to be resolved in the future, including: (1) how to harmonize the APG system and the morphology-based systems; (2) establishing new morphological evolution theories on the basis of the APG system; (3) determining whether it is enough to only use “monophyly” as a criterion to circumscribe orders and families; (4) determining morphological synapormorphies of those orders in the APG system; and (5) how to best compile a key to distinguish the orders and families of the APG system and to list their diagnostic characters for orders and families. In addition, we propose suggestions for the phylogenetic relationships and taxonomic status of some taxa mainly distributed in Asia, specifically East Asia, including Illiciaceae, Acanthochlamydaceae, Tetracentraceae, Leeaceae, Rhoipteiaceae, Hippocastenaceae, Aceraceae, Bretschneideraceae as familial status, and dividing Cornaceae sensu lato into Cornaceae sensu stricto and Nyssaceae sensu lato.

Key words: angiosperms, molecular systematics, classification, morphology, monophyly, synapormorphy