The document discusses the evolution of plant classification systems, particularly focusing on the Angiosperm Phylogeny Group (APG) classifications I-IV, which reflect phylogenetic relationships based on molecular data. APG III, published in 2009, introduced significant changes, recognizing 415 families and abandoning the controversial concept of bracketed families. The classification emphasizes monophyletic groups and integrates data from various biological disciplines, although it has limitations concerning the identification of flora and the status of certain families.

1. PLANT SYSTEMATICS
APG III CLASSIFICATION

2. “BEHOLD HER, SINGLE IN THE FIELD”

3. A PRESENTATION BY
DR. N. SANNIGRAHI, ASSOCIATE PROFESSOR
DEPARTMENT OF BOTANY,
NISTARINI COLLEGE, PURULIA,
D.B. ROAD, PURULIA (W.B) INDIA, 723101

4. PLANT CLASSIFICATION
 Until detailed genetic evidence became available, the classification of
flowering plants was based on their morphology (particularly that of the
flower) and their biochemistry (what kinds of chemical compound they
contained or produced). Classification systems were typically produced by
an individual botanist or by a small group. The result was a large number of
such systems. Different systems and their updates tended to be favored in
different countries; e.g. the Engler system in continental Europe; the
Bentham & Hooker system in Britain (particularly influential because it was
used by Kew); the Takhtajan system in the former Soviet Union and
countries within its sphere of influence; and the Cronquist system in the
United States. 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) that would reflect new knowledge about their relationships
based upon phylogenetic studies.
 The Taxonomy being synthetic science has been developed from time to
time by the addition of value in every respect.

5. PLANT CLASSIFICATION
 They set the most recent classification of flowering plants based on
phylogenetic data - the Angiosperm Phylogenetic Group classification. Its
four versions (APG I, APG II, APG III & APG IV) have been published in
1998, 2003, 2009 and 2016 respectively. Each version supplants the
previous version. Recognition of monophyletic group based on the
information received from various disciplines such as gross morphology,
anatomy, embryology, palynology, karyology, phytochemistry and more
strongly on molecular data with respect to DNA sequences of two
chloroplast genes (atpB and rbcL) and one nuclear gene (nuclearribosomal
18s DNA). The most recent updated version, APG IV (2016) recognized 64
orders and 416 families. Of these 416 families, 259 are represented in India.
 The Plant classification is very dynamic one with the passage of time and
more and more data input from the different domains of knowledge has
ultimately made the journey more fascinating and colorful.

6. PLANT CLASSIFICATION & APG
 In the early 1990s, the first large analyses of flowering plants based on
DNA sequences were published. These had become possible due to major
developments in DNA sequencing technology and computing power in the
late 20th century. Flowering plants were the first major group on which
large groups of scientists collaborated in comprehensive analyses of this
type, collecting sequences for the same genes, so that the data could be
combined. In 1993, a landmark paper with an analysis of 500 flowering
plants was published by Mark Chase, and co-authors, the year after Mark
moved from the University of North Carolina to Kew along with Brigittia
Bremer, Kare Bremer, Walter S. Judd, David J Mabberley, Peter F Stevens.
This paper was based on sequences of one of the major genes involved in
photosynthesis, and the analysis involved the botanists working with the
computer programmers because the program had to be rewritten to allow
them to analyze such a large data set. The Original APG system of Plant
classification based on cladistics analysis of DNA sequence .

7. PRINCIPLES OF APG SYSTEM
i. The principles of the APG’s approach to classification were set out in the
first paper of 1998 and it has remained unchanged in the subsequent
revisions like APGII, APGIII & APGIV. The basic principles are as
followed:
ii. The Linnaean system of orders and families should be retained.” The
family is central in flowering plant systematics”. An ordinal classification
of families as proposed as “reference tool of broad utility”. Orders are
treated for teaching and studying family relationship.
iii. Groups should be monophyletic i.e. all have been derived from common
ancestor. The main reason why existing systems are rejected because they
do not have the property , they are not phylogenetic.
iv. A broad approach is taken to defining the limits of the groups. Large
orders are considered more useful. Families with single genus and orders
having single family are kept out side. It is made so keeping monophyly
in view.
v. Named clades ate used to families and orders. The authors point out that
it is not possible or desirable to name all clades in phylogenetic tree;
naming some clades particularly orders and families make it easy to
exchange views and enhance discussion.

8. APG III CLASSIFICATION
 The APGIII system (2009) of plant classification is the third version of its
kind mostly based on molecular taxonomy and it was published after 6 and
½ years of APG II plant classification. Members of the Linnaean society put
forth a formal phylogenetic classification of all land plants , compatible with
the APG III.The system consists of 45 orders on the taxonomic rank and 14
new ones. The newly recognized orders are Amborellales, Nymphaeales,
Chloranthales, Petrosaviales, Trochodendrales, Buxales, Vitales,
Zygophyllales, Picramniales, Huerteales. Berberidopsidales, Escalloniales,
Bruniales and Paracryphiales.
 The alternative “Bracket families” were left out in APG III, because its
inclusion in the previous system had been unpopular .
 APG III recognizes 415 families, 42 fewer than the previous system. $$ of
the 55 bracketed families were discontinued and 18 other families were
discontinued.

9. APG III CLASSIFICATION
 The designation of alternative "bracketed families" was abandoned in APG
III, because its inclusion in the previous system had been unpopular. APG
III recognized 415 families, 42 fewer than in the previous system. Forty-
four of the 55 "bracketed families" were discontinued, and 18 other families
were discontinued as well. The discontinued bracketed families were:
Illiciaceae, Alliaceae, Agapanthaceae, Agavaceae, Aphyllanthaceae,
Hesperocallidaceae, Hyacinthaceae, Laxmanniaceae, Ruscaceae,
Themidaceae, Asphodelaceae, Hemerocallidaceae, Kingdoniaceae,
Fumariaceae, Pteridophyllaceae, Didymelaceae, Tetracentraceae,
Pterostemonaceae, Hypseocharitaceae, Francoaceae, Memecylaceae,
Lepuropetalaceae, Rhoipteleaceae, Medusagynaceae, Quiinaceae,
Malesherbiaceae, Turneraceae, Bretschneideraceae, Diegodendraceae,
Cochlospermaceae, Peganaceae, Tetradiclidaceae, Nyssaceae,
Ternstroemiaceae, Pellicieraceae, Aucubaceae, Donatiaceae, Lobeliaceae,
Desfontainiaceae, Diervillaceae, Dipsacaceae, Linnaeaceae, Morinaceae,
and Valerianaceae. The other discontinued families were: Limnocharitaceae,
Luzuriagaceae, Sparganiaceae, Ledocarpaceae, Heteropyxidaceae,
Psiloxylaceae, Oliniaceae, Rhynchocalycaceae, Parnassiaceae, Maesaceae,
Myrsinaceae, Theophrastaceae, Eremosynaceae, Polyosmaceae,
Tribelaceae, Aralidiaceae, Mackinlayaceae, and Melanophyllaceae

10. APG III CLASSIFICATION
 20 families were accepted in the APG III system which had not been in the
previous system, and a few families were moved to a different position. The
newly recognized families are: Petermanniaceae, Schoepfiaceae,
Limeaceae, Lophiocarpaceae, Montiaceae, Talinaceae, Anacampserotaceae,
Centroplacaceae, Calophyllaceae, Guamatelaceae, Gerrardinaceae,
Dipentodontaceae, Capparidaceae, Cleomaceae, Cytinaceae,
Mitrastemonaceae, Metteniusaceae, Linderniaceae, Thomandersiaceae, and
Quintiniaceae. The number of families not placed in any order was reduced
from 39 to 10. Apodanthaceae and Cynomoriaceae were placed among the
angiosperms, incertae sedis, that is, not in any group within the
angiosperms. Eight other families were placed incertae sedis in various
supra-ordinal groups within the angiosperms. The unplaced families were:
Apodanthaceae, Cynomoriaceae, Dasypogonaceae, Sabiaceae, Dilleniaceae,
Icacinaceae, Metteniusaceae, Oncothecaceae, Vahliaceae, and
Boraginaceae. The circumscription of the family Icacinaceae remains
especially doubtful. Apodytes, Emmotum, Cassinopsis, and a few other
genera were provisionally retained within it until further studies can
determine whether they properly belong there.

11. APG III CLASSIFICATION
 Three genera (Gumillea, Nicobariodendron, and Petenaea) were placed
within the angiosperms incertae sedis. Gumillea had been unplaced in APG
II. Nicobariodendron and Petenaea were newly added to the list. The
classification is shown below in two versions. The short version goes to the
level of orders and of families unplaced in an order. The detailed version
shows all the families. Orders at the same level in the classification are
arranged alphabetically. Note that orders may not contain the same families
as in earlier versions of the APG system (APG system, APG II system).
 Chase & Reveal ( 2009) gave a formal classification of land plants mainly
considering the algae in APG III. To keep harmony between hierarchical
classification and APG system, all land plants were included under
Equisetopsida. Angiosperm are divided into 15 super orders. All total 56
orders are listed of which, two Chloranthales are unplaced . Further seven
families could not be accommodated.

12. APG III CLASSIFICATION

13. MERITS OF THE CLASSIFICATION
i. The system shows monophyly origin in groups,
ii. The system covers the multiple data from morphology, anatomy,
embryology, phytochemistry & molecular data.
iii. Groups names up to orders have been assigned,
iv. Traditional divisions of the angiosperms into monocotyledons and
dicotyledons has not been taken into account. Many monocots are put in
between primitive angiosperms and eudicots. It can solve the problem of
paraphyly among monocots and dicots in the early stages.
v. A number of cladograms in the classification shows general affinities
between the various groups of organisms.
vi. Primitive families are placed at the beginning of the angiosperms.
vii. The merger of Budlejaceae and Myotoraceae with Scrophulariaceae have
been supported from morphological and molecular evidences given by
Bremer et.al (2001) and Olmstead et.al (2001).
viii. Multigene analysis and morphological data are the basis on which
Winteraceae and Cancellaceae are kept under the same order.

14. MERITS & DEMERITS OF THE CLASSIFICATION
 Family Agavaceae includes genera like Hosta, Camassina and Chlorogalum
and it becomes more wide. This justification has been supported by Judd
et.al (2002) and Thorne.
 Monophyletic concept is reflected in Malvaceae where families like
Tiliaceae, Sterculariaceae and Bombaceae are included in the former. This
inclusion is supported by molecular as well as morphological data.
 Asclepidaceae has been merged with Apocynaceae. This view is supported
and strengthened by Judd et.al (1994) from molecular evidence.
 The concept of bracketed families in earlier APG has been removed in APG
III.
 DEMERITS
 This classification is only applicable up to families. This system is not
suitable for identification of flora in the true sense.
 The fate of some unplaced families and few replaced genera is still
uncertain.
 Botanical nomenclature Code has not been assigned to new group.

15. ACKNOWLEDGMENT
 Google for images,
 Different websites for content and enrichment,
 Text Book of Plant Systematics- Chittaranjan Mohanty
 Plant Taxonomy by O.P. Sharma,
 Taxonomy of angiosperms- Nayek.
 Plant Taxonomy- Gurucharan Singh
 A text Book of Botany- Hait, Bhattacharyya & Ghosh
 Advanced Plant Taxonomy- A.K. Mondal.
 Disclaimer: This presentation has been developed to enrich free open source
of the study materials for Biology students without any financial issues.

16. THANK YOU FOR YOUR JOURNEY