Depending upon the presence or absence of flowers and seeds entire classification of plant kingdom is divided into two types. They are
- Cryptogamae and
- Cryptogams include all non-flowering plants such as algae, fungi, lichens, mosses and fern (Kryptos: concealed; gamus: marriage).
- Cryptogamae is further subdivided into three parts: Thallophyta, Bryophyta and Pteridophyta.
- Both Algae and Fungi are considered in Thallophyta, but nutrition in autotropic in algae, whereas fungi exhibit heterotropic nutrition. Algae usually sustain itself in a variety of habitats such as wetland as well as on other plants and even animals. Some grow in marine water and are called seaweeds.
- A variety of pigments in algae provide different colours. The green algae have mainly chlorophyll-a and chlorophyll-b along with carotenoids as photosynthetic pigments.
- Algae reproduce vegetatively by fragmentation, budding or tuber formation.
- Based on pigment colour, nature of stored food material and cell organization, algae are further sub-divided into green (chlorophyceae), brown (Phaeophyyceae) and red (Rhodophyceae), etc.
- Bryophyta derives its name from mosses which grow on the rocks, walls and tree trunks in moist and shady places.
- Bryophyta type of plants don’t have roots, flowers and seeds.
- Mosses also retain moisture like the sponges.
- The members of this group reproduce both vegetatively through fragmentation, gemmae and tubers as well as by sexual methods.
- Based on the structure of plant body and the method of sexual reproduction, bryophytes are divided into three classes: Hepaticae (Liverwort), Anthocerotae (Hornwort) and Musci.
- Pteridophyta derives its name from the fern.
- They occur in humid and tropical climates and usually grow on soil, rocks, in ponds and as epiphytes on other plants.
- The pteridophytes have primitive vascular system.
- On the basis of organization of plant including the nature of leaf, vascular system and location of sporangia, the Pteridophyta is divided into four classes, as Psilopsida, Lycopsida, Sphenopsida and Pteropsida.
- Phanerogamae are also known as spermatophytes.
- Phanerogamae includes all flowering plants which bear seeds. (Phaneros: visible; gamus: marriage).
- Phanerogams are further subdivided into two parts: Gymospermae and Angiospermae.
- The Gymnosperms are represented by the cyads, pines and cedar. Gymnosperms have the naked (uncovered) seeds i.e the seeds are not enclosed in a fruit.
- Angiosperms have covered seeds i.e. they are always enclosed in an ovary or fruit.
- Gymnosperms are represented by conifers, which grow in cool climate of hills, sometimes using melting snow as a source of water. however, some like cycads and members of gnetales thrive in warm dry climate.
- The Abides, Cedrus, Pinus and other timber-yielding species are some common gymnosperms.
- Gymnosperms are further divided into 3 classes – Cycadopsida, Coniferopsida and Gnetopsida on the basis of nature of leaves, woods, vascular system and reproductive structures.
- Angiosperms range in size from minute floating duckweeds to gaint eucalyptus and silk cotton trees and include plants of great variety and form-cacti, water lillies, sunflowers, orchids, pitcher plants, Indian pipe etc.
- The angiosperms are seed-bearing plants well adapted to the terrestrial life and they occur in diverse habitats like cold tundra to hot tropical and even desert areas. They also thrive well in aquatic habitats.
- Angiosperm plants represented by trees, shrubs and herbs are either monocotyledons or dicotyledons. they have a body well differentiated into root, stem and leaves.
- The phenomenon of pollination. i.e. transfer of pollens from stamens to carpels, is an unique mechanism in angiosperms. It is facilitated by wind, water, insects, birds and other animals including man.
- There are two main classes of Angiosperms: a) Dicotyledons and b) Monocotyledons.
The leaves in members of Dicotyledons class exhibit reticulate (net-like) venation and show varied arrangement like alternate, spiral or whorled. The flowers are tetramerous or pentamerous having four or five members in the various floral whorls, respectively. The vascular bundles are open, i.e cambium is present between the xylem and phloem. The seeds of dicotyledons are with two cotyledons.
The leaves of Monocotyledons are simple with a parallel venation. the vascular bundles are closed (cambium absent) and scattered in the parenchyma. the flowers are trimerous having 3 members only one cotyledon.