Plant Kingdom

• PLANT KINGDOM
• In the previous chapter, we looked at the broad classification of living organisms under the system proposed by Whittaker (1969) wherein he suggested the Five Kingdom classification viz. Monera, Protista, Fungi, Animalia and Plantae. In this chapter, we will deal in detail with further classification within Kingdom Plantae popularly known as the 'plant kingdom'.
• Fungi, and members of the Monera and Protista having cell walls have now been excluded from Plantae though earlier classifications placed them in the same kingdom. So, the cyanobacteria that are also referred to as blue green algae are not 'algae' any more.
• In this chapter, we will describe Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms under Plantae.
• The earliest systems of classification used only gross superficial morphological characters such as habit, colour, number and shape of leaves, etc. They were based mainly on vegetative characters or on the androecium structure (system given by Linnaeus). Such systems were artificial; they separated the closely related species since they were based on a few characteristics.
• As against this, natural classification systems developed, which were based on natural affinities among the organisms and consider, not only the external features, but also internal features, like ultra-structure, anatomy, embryology and phytochemistry.
• At present phylogenetic classification systems based on evolutionary relationships between the various organisms are acceptable. This assumes that organisms belonging to the same taxa have a common ancestor.
• Numerical Taxonomy which is now easily carried out using computers is based on all observable characteristics. Number and codes are assigned to all the characters and the data are then processed. In this way each character is given equal importance and at the same time hundreds of characters can be considered.
• Cytotaxonomy that is based on cytological information like chromosome number, structure, behaviour and chemotaxonomy that uses the chemical constituents of the plant to resolve confusions, are also used by taxonomists these days.
• Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic (both fresh water and marine) organisms. They occur in a variety of other habitats: moist stones, soils and wood. Some of them also occur in association with fungi (lichen) and animals (e.g., on sloth bear).
• Algae

  • The form and size of algae is highly variable, ranging from colonial forms like Volvox and the filamentous forms like Ulothrix and Spirogyra. A few of the marine forms such as kelps, form massive plant bodies.
• Algal reproduction

  • Vegetative
  • Asexual
  • Sexual
• Vegetative reproduction

  By fragmentation. Each fragment develops into a thallus.
• Asexual reproduction


  By the production of different types of spores, the most common being the zoospores. They are flagellated (motile) and on germination gives rise to new plants.
• Sexual reproduction

  Takes place through fusion of two gametes. These gametes can be flagellated and similar in size (as in Ulothrix) or non-flagellated (non-motile) but similar in size (as in Spirogyra). Such reproduction is called isogamous. Fusion of two gametes dissimilar in size, as in species of Eudorina is termed as anisogamous. Fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete is termed oogamous, e.g., Volvox, Fucus.
• Algae are useful to man in a variety of ways. At least a half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis. Being photosynthetic they increase the level of dissolved oxygen in their immediate environment. They are of paramount importance as primary producers of energy-rich compounds which form the basis of the food cycles of all aquatic animals.
• Algae used as food

  • Porphyra, Laminaria and Sargassum
• Algae that produce hydrocolloids

  • Brown algae (algin)
  • Red algae (carrageen)
• Algae used to grow microbes and in preparations of ice-creams and jellies

  • Agar (from Gelidium and Gracilaria)
• Algae used as food supplement

  • Chlorella (a unicellular alga rich in proteins)
• Classes of algae

  • Chlorophyceae (green algae)
  • Phaeophyceae (brown algae)
  • Rhodophyceae (red algae)
• Chlorophyceae (green algae)


  • The plant body may be unicellular, colonial or filamentous. They are usually grass green due to the dominance of pigments chlorophyll a and b. The chloroplasts may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplasts. Green algae usually have a rigid cell wall made of an inner layer of cellulose and an outer layer of pectose.
• Phaeophyceae (brown algae)

  • They possess chlorophyll a, c, carotenoids and xanthophylls. They vary in colour from olive green to various shades of brown depending upon the amount of the xanthophyll pigment, fucoxanthin present in them. Food is stored as complex carbohydrates, which may be in the form of laminarin or mannitol. The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin. The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and leaf like photosynthetic organ – the frond.
• Rhodophyceae (red algae)


  • The red thalli of most of the red algae are multicellular. Some of them have complex body organisation. The food is stored as floridean starch which is very similar to amylopectin and glycogen in structure.
• Characteristics of algal divisions

  • Chlorophyceae: Pigments - Chlorophyll a, b; Stored food - Starch; Cell wall - Cellulose; Flagella - 2-8, equal, apical
  • Phaeophyceae: Pigments - Chlorophyll a, c, fucoxanthin; Stored food - Mannitol, laminarin; Cell wall - Cellulose; Flagella - 2, unequal, lateral
  • Rhodophyceae: Pigments - Chlorophyll a, d, phycoerythrin; Stored food - Floridean starch; Cell wall - Cellulose, pectin and polysulphate esters; Flagella - Absent
• Bryophytes include the various mosses and liverworts that are found commonly growing in moist shaded areas in the hills.
• Bryophytes


  Also called amphibians of the plant kingdom because these plants can live in soil but are dependent on water for sexual reproduction.
• Bryophyte plant body


  • More differentiated than that of algae. It is thallus-like and prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids. They lack true roots, stem or leaves. They may possess root-like, leaf-like or stem-like structures.
• Bryophyte life cycle

  The main plant body of the bryophyte is haploid. It produces gametes, hence is called a gametophyte. The sex organs in bryophytes are multicellular. The male sex organ is called antheridium. They produce biflagellate antherozoids. The female sex organ called archegonium is flask-shaped and produces a single egg. The antherozoids are released into water where they come in contact with archegonium. An antherozoid fuses with the egg to produce the zygote. Zygotes do not undergo reduction division immediately. They produce a multicellular body called a sporophyte. The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it. Some cells of the sporophyte undergo reduction division (meiosis) to produce haploid spores. These spores germinate to produce gametophyte.
• Bryophytes in general are of little economic importance but some mosses provide food for herbaceous mammals, birds and other animals. Species of Sphagnum, a moss, provide peat that have long been used as fuel, and as packing material for trans-shipment of living material because of their capacity to hold water.