APG classification

Angiosperm Phylogeny Group classification

1. APG (Angiosperm Phylogeny Group) III classification
Ashutosh Mukherjee
Department of Botany, Vivekananda College, 269, Diamond Harbour Road, Thakurpukur, Kolkata
- 700063, West Bengal, India.

The Angiosperm Phylogeny Group, or APG, refers to an informal international group of
systematic botanists who came together to try to establish a consensus view of the taxonomy of
flowering plants (angiosperms). APG (Angiosperm Phylogeny Group) system is a modern, mostly
molecular evidence based phylogeny of flowering plants. The first APG classification was
published in 1998 followed by APG II in 2003, APG III in 2009 and APG IV in 2016. APG
classification was based on two chloroplast and one ribosomal genes.
The overall principles of the APG's approach to classification are:
1. The Linnean system of orders and families should be retained. "The family is central in
flowering plant systematics." An ordinal classification of families is proposed as a
"reference tool of broad utility". Orders are considered to be of particular value in teaching
and in studying family relationships.
2. Groups should be monophyletic (i.e. consist of all descendants of a common ancestor). The
main reason why existing systems are rejected is because they do not have this property,
they are mostly not phylogenetic.
3. A broad approach is taken for defining the limits of groups. Thus of orders, it is said that a
limited number of larger orders will be more useful. Families containing only a single
genus and orders containing only a single family are avoided where this is possible without
violating the over-riding requirement for monophyly.

Structure of APG III system
As APG is based on cladistic approach, it does not always refer formal groups. However, it
includes 59 orders and 415 families. The higher order classification divided the whole angiosperms
into different clades like the following:

2. Clade angiosperms (4 orders; eg: Amborellales, Nymphaeales)
Clade magnoliids (4 orders; eg: Magnoliales, Piperales)
Clade monocots (7 orders; eg: Acorales, Alismatales, Asparagales)
Clade commelinids (4 orders: Arecales, Commelinales, Poales and Zingiberales; 1 family)
Probable sister of Eudicots (order Ceratophyllales)
Clade eudicots (4 orders; eg: Ranunculales; 1 family unplaced in an order)
Clade Core Eudicots (2 orders; eg: Saxifragales; 1 family unplaced in an order)
Clade Rosids (Order Vitales)
Clade Fabids (8 orders; eg: Cucurbitales, Fabales)
Clade Malvids (8 orders; eg: Brassicales; Malvales)
Clade Asterids (orders Cornales and Ericales)
Clade Lamiids (5 unplaced families and 4 orders; eg: Lamiales, Solanales)
Clade Campanulids (7 orders; eg: Apiales, Asterales)

Merits
1. It adopts the phylogenetic principle of monophyly.
2. It has derived information from sources like morphology, embryology, molecular
biology, anatomy, palynology and phytochemistry.
3. Formal names are given only where monophyly has been firmly established.
4. It is based on the recent advances in research and is gaining authority.
Demerits
1. It is limited to the taxonomic level of order and family.
2. It is not very popular.
3. Several families or genera have not been placed yet.
4. The orders are recognized under informal groups like Magnoliids, Eudicots. These names
do not conform to the ICN.