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Chapter: 11th Botany : Chapter 5 : Taxonomy and Systematic Botany

Angiosperm phylogeny group (APG) classification

The most recent classification of flowering plants based on phylogenetic data was set in the last decade of twentieth century.


Angiosperm phylogeny group (APG) classification


The most recent classification of flowering plants based on phylogenetic data was set in the last decade of twentieth century. Four versions of Angiosperm Phylogenetic Group classification (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 (nuclear ribosomal 18s DNA).

 

The most recent updated version, APG IV (2016) recognised 64 orders and 416families. Of these, 416 families 259 are represented in India.

 

The outline of APG IV classification is given below.


Angiosperms are classified into three clades early angiosperms, monocots and eudicots. Early angiosperms are classified into 8 orders and 26 families (ANA-grade + magnoliids + Chloranthales)

Amborellales Nymphaeales Austrobaileyales

 

      Seeds always with two cotyledons.

 

      Presence of ethereal oils.

 

      Leaves are always simple net-veined.

 

      Each floral whorls with many parts.

 

      Perianth usually spirally arranged or parts in threes.

 

      Stamens with broad filaments.

 

      Anthers tetrasporangiate.

 

      Pollen monosulcate.

 

      Nectaries are rare.

 

      Carpels usually free and.

 

      Embryo very small.


Monocots are classified into 11 orders and 77 families (basal monocots + lilioids + commelinids)

 

      Seeds with single cotyledon.

 

      Primary root short-lived.

 

      Single adaxial prophyll.

 

      Ethereal oils rarely present.

 

      Mostly herbaceous, absence of vascular cambium.

 

      Vascular bundles are scattered in the stem.

 

      Leaf simple with parallel-veined.

 

      Floral parts usually in threes.

 

      Perianth often composed of tepals.

 

      Pollen monosulcate.

 

      Styles normally hollow and.

 

      Successive microsporogenesis.

 

Eudicots are divided into 45 orders and 313 families (early diverging eudicots + super rosids + super asterids).

 

      Seeds with always two cotyledons.

 

      Nodes trilacunar with three leaf traces.

 

      Stomata anomocytic.

 

      Ethereal oils rarely present.

 

      Woody or herbaceous plants.

 

      Leaves simple or compound, usually net-veined.

 

      Flower parts mostly in twos, fours or fives.

 

      Microsporogenesis simultaneous.

 

      Style solid and .

 

      Pollen tricolpate.

 

APG system is an evolving system that might undergo change periodically based on the new sets of data from various disciplines of Botany. It is the currently accepted system across the world and followed by all the leading taxonomic institutions and practising taxonomists. However, it is yet to percolate into the Indian botanical curriculum.

 



Classification reflects the state of our knowledge at a given point of time. It will continue to change as we acquire new information.


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