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03 PLANT KINGDOM
114 PLANT KINGDOM SCAN CODE Plant Kingdom Chapter 03 Plant Kingdom  The plant kingdom consists of few unicellular and mostly multicellular eukaryotic organisms that are capable of photosynthesis.  Classification of the Plant Kingdom has changed over time.  Fungi and members of the Monera and Protista having cell walls have now been excluded from Plantae, though earlier classifications (two-kingdom classification system) put them in the same kingdom.  Cyanobacteria that are also referred to as blue-green algae are not members of the kingdom Plantae anymore.  The broad classification of living organisms was proposed by Whittaker (1969) wherein he suggested the Five Kingdom classification viz. Monera, Protista, Fungi, Animalia and Plantae. Monera Protista Fungi Cyanobacteria Fig 3.1: Earlier placed in the Plant Kingdom 1. Systems of Classification  The broad classification of living organisms was proposed by Whittaker (1969) wherein he suggested the Five Kingdom classification viz. Monera, Protista, Fungi, Animalia and Plantae.  There are mainly three types of classification systems:
PLANT KINGDOM 115 SCAN CODE Plant Kingdom 1.1 Artificial System of Classification  The artificial system of classification used only gross superficial morphological characters such as habit, colour, number, and shape of leaves, etc. for classification.  It was based mainly on vegetative plant parts (such as roots, shoots, stem, leaves) or on the androecium structure. This system was given by Carolus Linnaeus. Colour of flower Leaf Shape Androecium Fig 3.2: Morphological characters for artificial classification Fig 3.3: Carolus Linnaeus Disadvantages of Artificial system of Classification  It separated the closely related species since this system was based on a few characteristics.  The artificial systems gave equal weightage to vegetative and sexual characteristics. This is not acceptable as we know that vegetative characters such as leaf size and shape, etc. are more easily affected by the environment. 1.2 Natural System of Classification  The natural system of classification was not just based on the external features but also internal features, like anatomy, ultrastructure, embryology, and phytochemistry. These characters are relatively constant. Types of Classification Artificial System Natural System Phylogenetic System
116 PLANT KINGDOM SCAN CODE Plant Kingdom Anatomy Ultrastructure Embryology Fig 3.4: Internal features for natural classification system  It is a system of classification which takes into consideration comparable study of a number of characters so as to bring out natural similarities and dissimilarities and hence, natural relationships among organisms.  George Bentham and Joseph Dalton Hooker gave a Natural system of classification. They described their study in the book 'Genera Plantarum'. Fig 3.5: George Bentham (Left), Joseph Dalton Hooker (Middle), Genera Plantarum (Right) Why do we prefer natural classification over artificial classification?  The natural classification system uses multiple characters for classification which minimizes the chance of placing unrelated organisms in a group.  It includes homology in all characters.  It gives information about both natural relationships and phylogeny.  It does not consider habit or habitat as criteria for classification. 1.3 Phylogenetic System of Classification  The first phylogenetic system was proposed by Engler and Prantl.  It is based on evolutionary relationships between various organisms.  Fossil records are the major source of information.  A phylogenetic system is not static but highly dynamic. As newer fossils are discovered, newer relationships are observed, and consequently, the phylogenetic system is changed and updated.  This system assumes that organisms belonging to the same taxa have a common ancestor.