PLANT KINGDOM

INTRODUCTION
• Plant kingdom includes eukaryotic, autotrophic or photosynthetic and non-motile organisms.
• Plant kingdom includes five major plant groups i.e. Algae, Bryophyte, Pteridophyte, Gymnosperms
and Angiosperms as proposed by R.H. Whittaker in 1969.
• Main characters of plant kingdom are–
• presence of cellulosic cell wall.
• non-motile, except some aquatic forms.
• reproduction is primarily sexual.
• photosynthetic mode of nutrition, e.g., different types of algae (green, brown, red algae), bryophytes,
gymnosperms and angiosperms.

TYPES OF CLASSIFICATION
• There are various types of classification in angiospermic plants.
• All taxonomists, from Aristotle to Linnaeus, proposed artificial system of classification.
• Artificial system of classification is based on few morphological characters. It is primitive or oldest
system of classification.
• Natural system of classification was based on all the possible characters and therefore, this system is
practically more useful.
• Phylogenetic system of classification was proposed by "Sokel and Sneath". Plants are classified on
the basis of numbers of similarities and dissimilarities. In this, importance to any one character is not given, all
characters have the same importance. While, in natural classification, floral (reproductive) characters have
more importance than vegetative (root, stem and leaves) characters.
• In Traditional system of classification (Eichler, 1883), plant kingdom is divided into two
subkingdoms-cryptogams and phanerogamae (Refer flow chart 3.1)

ALGAE
• The branch of botany dealing with the study of algae is called phycology or algology.
• Structure and reproduction of algae was written by Fritsch. He is known as the father of algae.
• Algae are defined as chlorophyllous and thalloid avascular plants with no cellular differentiation.
• Algae are plants because they have chlorophyll a, cellulosic cell wall and starch as reserve food.
• Large marine algae are generally known as seaweeds or kelps.
• Algae are mostly found in fresh water as well as in salt water.
• They occur in a variety of other habitats also like moist stones, soils and wood.
• The body or thallus of multicellular algae ranges from microscopic unicellular (Chlamydomonas),
colonial (Volvox), aggregates of cells, fine filaments (Ulothrix), to flattened sheets of cells.
• All kinds of reproduction are found in algae like vegetative, asexual and sexual.
• Vegetative reproduction occurs through fragmentation. Each fragment develops into a thallus.
• Asexual reproduction occurs through the production of different types of spores like zoospores,
hypnospores, akinetes, endospores, cysts, etc. 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.
• Sexual reproduction is of two types on the basis of the size of gametes–Isogamous and heterogamous
(anisogamous and oogamous).
• Isogamy occurs commonly in unicellular algae, where male and female gametes are morphologically
similar but differ in physiology. E.g., Ulothrix.
• Anisogamy is the fusion of gametes where male gametes are comparatively smaller in size and more
active than female gametes which are larger and sluggish. E.g. Chlamydomonas.
• Oogamy is the most advanced type of sexual reproduction where fusion of one large, non-motile
(static) female gamete with a smaller motile male gamete takes place. E.g. Volvox, Fucus.
• Water a suitable medium for the fusion of gametes during sexual reproduction.
Table : Common names of Algae
• Plants growing on snow or ice are called as cryophytes. Different algal forms produce a specific
colour effect while growing as cryophyte. E.g., yellow-green by Chlamydomonas yellowstonensis, red by C.
nivalis, black by Scotiella nivalis and purple-brown by Ancylonema nordenskioldii.
• Plants growing in hot water are called as thermophytes. Some blue-green algae grow in hot water
springs at about 70°C. E.g., Oscillatoria brevis.
• Several algal forms grow on other plants (algae, angiosperms) as epiphytes. E.g., Oedogonium,
Cladophora, Vaucheria, etc.
• Some blue-green algae grows as endophytes inside other plants. E.g., Anabaena growing inside the
leaf of Azolla (fern), Nostoc inside the thallus of Anthoceros (hornwort) and Anabaena, Nostoc, Oscillatoria
inside the coralloid roots of Cycas.
• Algae growing on the bodies of animals are described as epizoic. E.g., Cladophora crispata grows on
snail shell, Characium grows on the antennae of mosquito larvae, Cyanoderma (red alga) and Trichophilus
(green alga) grows on scales of sloth.
• Algae growing inside the body of animals are called endozoic. E.g., Chlorella grow within the tissue
of Hydra. Some blue-green algae also grow in the respiratory tracts of animals. The blue-green algae which
grow endozoically inside the protozoans are called as cyanellae.
• Some algae like Chlorella, Nostoc, etc. growing in symbiotic relationship with members of
Ascomycetes and Basidiomycetes (Fungi) constitute the lichen.
• The alga Cephaleuros virescens grows as a parasite on the tea leaves. In addition, Rhodochytrium,
Phyllosiphon are other parasitic algal forms.
• Several members of algae are unicelled. They may be motile (Chlamydomonas) or non-motile
(diatoms). Some forms have a thick wall and become sedentary for certain duration in their life history. They
are called as coccoid. E.g., Chlorella, Chlorococcus etc.
• Most of the algal groups (except blue-green and dinoflagellates) shows eukaryotic cell structure. The
cell wall is made up of cellulose. Some red algae (Corallina) have impregnation of CaCO3.
• The red alga Cephaleuros virescens causes red rust of tea thus destroying the tea leaves. Similar
diseases are caused by the species of Cephaleuros to coffee plant, Piper and Citrus sp.
• Algae grow abundantly in water reservoirs where excess of nutrients are available to them. This algal
growth floats on the water surface and look like foam or soap lather. It is called water bloom. E.g.,
Microcystis, Anabaena, Oscillatoria, etc.
• Algae are useful to man in a variety of ways, like-
o Chlorella and Spirulina are used as food and fodder. Chlorella is rich in protein and
carbohydrates. Spirulina platensis is one of the richest sources of protein.
o Certain marine brown algae and red algae produce large amounts of hydrocolloids (water
holding substances). E.g.- Alginic acid are extracted from the members of phaeophyceae such as Laminaria,
Macrocystis and Carrageenan is extracted from red algae Chondrus crispus. (Irish moss).
o Agar, dried gel like non-nitrogenous extract from red algae, is used as a medium in the
cultures of bacteria, fungi and algae. It is largely prepared from Gelidium.
o Laminaria digitata and Fucus sp. are largely known for the extraction of iodine, hence used to
treat goitre.

CLASSIFICATION OF ALGAE
Fritsch divided algae into 11 classes on the basis of type of pigments, nature of reserve food material and
mode of reproduction. The three major classes are - Chlorophyceae, Phaeophyceae and Rhodophyceae.

Table : Divisions of algae and their main characteristics

CHLOROPHYCEAE

• Chlorophyceae are commonly called as green algae.

• Most green algae live in fresh waters and few are marine. Some are terrestrial and some can grow
anywhere on moist surface.
• The plant body may be unicellular, colonial or filamentous.
• They are usually green in colour due to the dominance of pigments chlorophyll a, b and xanthophyll,
which are localized in definite chloroplasts.
• Chloroplast generally contain one or more storage bodies called pyrenoids. Pyrenoids contain proteins
besides starch. Some algae may store food in the form of oil droplets also.
• Green algae usually have a rigid cell wall made of an inner layer of cellulose and an outer layer of
pectose. They store starch. For these reasons, they are believed to be ancestors of land plants.
• Vegetative reproduction usually takes place by fragmentation or by formation of different types of
spores.
• Asexual reproduction is by flagellated zoospores produced in zoosporangia.
• The sexual reproduction shows considerable variation in the type and formation of sex cells and it
may be isogamous, anisogamous or oogamous.
• Green algae exhibit three types of life cycles-haplontic, diplontic and diplohaplontic. Examples are :
Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara.

SPIROGYRA
• It is an unbranched filamentous green alga of stagnant fresh waters which forms floating masses
(supported by bubbles of oxygen) called pond scum. A sheath of mucilage occurs on the outside. It gives a
silky touch. Hence, Spirogyra is also called water silk or mermaid’s tresses.
• The thallus is an unbranched and uniseriate filament where cells are arranged in a single row. In some
species, hold fast is present (e.g., S. fluviatilis).
• The cells are elongated and cylindrical.
• The cell wall is two layered–the outer is of pectic substance and the inner of cellulose. The outer part
(pectin) dissolves in water to form a mucilaginous sheath. Due to this reason, Spirogyra filaments are slippery.
• Ribbon (spiral) shaped chloroplasts (wavy margin) with pyrenoids and a large central vacuole.
• Nucleus occurs inside the central vacuole where it is suspended by means of cytoplasmic strands.

• Normally, asexual reproduction is absent in Spirogyra. It occurs only occasionally by the formation of
akinetes, aplanospores and azygospores (parthenospores).
• Sexual reproduction takes place towards the end of growing season usually in the late spring. Sexual
reproduction in Spirogyra is called conjugation. It involves the fusion of two morphologically identical, but
physiologically dissimilar gametes.

ULOTHRIX
• It is a green unbranched filamentous algae found in slow running streams. The common species
U.zonata occurs in cold water whereas U.flacca is marine. U.implexa occurs in estuaries (where river meets the
sea) as lithophytes.
• Due to presence of protopectin, Ulothrix filaments appear as wet threads.
• The Ulothrix reproduces vegetatively, asexually as well as sexually.
• Asexual reproduction occurs through fragmentation, zoospores, palmella stage, aplanospores,
hypnospores and akinetes.
• Sexual reproduction occurs through isogamy.
• Life cycle is haplontic.

PHAEOPHYCEAE

• The phaeophyceae are commonly called as brown algae.

• They are found primarily in marine habitats.
• They range from simple branched, filamentous forms (Ectocarpus) to profusely branched forms as
represented by kelps, which may reach a height of 100 metres.
Fig. : Brown algae

• They possess chlorophyll a, c, carotenoids and xanthophylls (such as fucoxanthin for brown colour
and diatoxanthin).
• Food is stored as complex carbohydrates, in the form of laminarin or mannitol.
• The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of
alginic acid. The protoplast contains, in addition to plastids, a centrally located vacuole and nucleus.
• The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and leaf
like photosynthetic organ-frond.
• Vegetative reproduction takes place by fragmentation.
• Asexual reproduction in most brown algae is by biflagellate zoospores that are pear-shaped and have
two unequal laterally attached flagella.
• Sexual reproduction may be isogamous, anisogamous or oogamous. Union of gametes may take
place in water or within the oogonium (oogamous species). The gametes are pyriform (pear-shaped) and bear
two laterally attached flagella.
• Life cycle is diplohaplontic or diplontic.
• The common forms are Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.

RHODOPHYCEAE

• Rhodophyta are commonly called red algae because of the predominance of the red pigment, r-
phycoerythrin in their body. Majority of the red algae are marine with greater concentrations found in the
warmer areas.
They occur in both well-lighted regions close to the surface of water and also at great depths in oceans where
relatively little light penetrates.

Fig. : 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.
• The red algae usually reproduce vegetatively by fragmentation.
• They reproduce asexually by non-motile spores and sexually by non-motile gametes.
• Sexual reproduction is oogamous and accompanied by complex post fertilization developments.
• The common members are: Polysiphonia, Porphyra Gracilaria, Gelidium and Batrachospermum.
• Batrachospermum is the only freshwater algae found growing in well aerated water but it is not red.