Division of Plant Kingdom | Botany

In this article we will discuss about the cryptogams and phanerogams divisions of plant kingdom.

I. Cryptogams:

Cryptogams never bear flowers and reproduce by some minute bodies called spores, or by simple fission.

They are again divided into three groups:

(a) Thallophyta:

A thallophyte is that plant where the plant body is an undifferentiated mass of cells (thallus), having nothing like stems, roots and leaves. The green thallophytes which usually grow in water are called algae, e.g. pond-scum; and non-green thallophytes are the fungi. The common moulds growing on rotten organic substances and mushrooms, belong to this group.

(b) Bryophyta:

This group includes plants like mosses with small stems and simple leaves but no roots. They grow in moist places often forming something like green velvety carpet. Some bryophytes have thalloid bodies.

(c) Pteridophyta:

Here the plant body is well differentiated into roots, stems and leaves, and the organs have well-developed conducting strands. These are the highest cryptogams also known as vascular cryptogams. Ferns are the familiar examples.

II. Spermatophytes or Phanerogams:

These are the higher plants. They bear flowers and reproduce by means of seeds. They are of two types: Gymnosperms (gymnos = naked; sperma = seed) and Angiosperms (angeion—a case). Gymnosperms are the naked-seeded plants where the seeds remain exposed; but the angiosperms are closed-seeded ones where seeds are covered, that is, remain inside the fruits.

Almost all the flowering plants with which we are familiar belong to this group. Angiosperms are dicotyledonous or monocotyledonous, according to the number of cotyledons present in the embryo. Pea, mango, jack-fruit, etc., are dicotyledons, and rice, maize, palms, etc., are monocotyledons.

It may be of interest to note that more than 340,000 plants have been iden­tified, described and named by the botanists. Approximately 110,000 of them are thallophytes, 20,000 bryophytes, 10,000 pteridophytes and nearly 200,000 are spermatophytes.

The above classification proves beyond doubt that in the plant kingdoms there is a gradual ascent in complexity of structure from the lowest thallophytes to the highest angiosperms. Gradual adapt­ability to terrestrial habitable from aquatic is also a notable feature.

Apart from this systematic classification, the plants are also grouped on the basis of their mode of nutrition. We know that the green plants can manufacture complex organic food matters from the raw materials, water and carbon dioxide gas, in the presence of sunlight.

So they are self-supporting and are called autophytes. Plants like Cuscuta or dodder (B. Swarnalata) do not manufacture food but grow on some other plants, referred to as ‘hosts’, and absorb sap from the host by sending out peculiar sucking roots (Fig. 44,2).

They are called parasites. Parasites may be total or partial. Cuscuta and Rafflesia (Fig. 16), which produces the biggest flowers, a yard in diameter and nearly 25 lbs. in weight (native of Java and Sumatra), are total parasites.

Sapria Himalayan, found in Eastern most part of India are just like Rafflesia, but smaller in size. ‘Loranthus or mistle­toe and sandal wood trees are known as partial parasites, because in addition to the sucking roots they also produce thick leaves for manufacture of food.

Some orchids grow on the stout branches of trees and produce roots which freely hang in air. These roots are sometimes green in colour, and owing to presence of a tissue known as ‘velamen’ can absorb moisture from air.

They are called epiphytes (Fig. 43). Fungi like moulds and mushrooms grow on dead rotten organic matters and draw nourishment from them. These plants are saprophytes. Roots of leguminous plants like pea and pulses are infected by some nitrogen-fixing bacteria which form swellings or nodules.

These bacteria fix free nitrogen from the atmosphere and supply the same to the plant, and, in return, they get other food matters from, the plant.

Thus the bacteria and the plant lead a life of mutual friendship, re­ferred to as sym­biosis. They are called symbionts. The insectivorous or car­nivorous plants are very interesting. Some of their organs are modified into structures suitable for attracting and catching insects. Those plants draw part of their nitrogenous food requirement from the bodies of the insects they catch.

Nepenthes or pitcher plant is a small herbaceous plant in which the leaf-blade is modified into a hollow pitcher with interesting device for catching insect. Drosera or sundew is another small insectivorous plant. It has spatula-like leaves bearing glandular tentacles the tips of which glisten in sunshine like dew- drops.

These sensitive tentacles actually are responsible for catching insects. Utricularia or bladderwort is a common aquatic plant with segmented leaves. Some of the leaflets are modified into swollen blad­ders for catching insects.

According to habitat or situations where they grow, plants may be classified as follows:

Hydrophytes or water plants grow in water or places with plenty of water. They are normally delicate plants with poorly developed roots, segmented or ribbon-like leaves, soft and spongy stems with abundant air-spaces. Vallisneria (B. Pata shaola), water hyacinth, lotus, lily are the examples.

Mesophytes are common land plants growing in moderate water supply. They stand midway between water plants and desert plants as regards structural peculiarities, possessing broad and thin leaves with stomata and well-developed roots with root-hairs.

Xerophytes are plants of deserts—very dry situations with ex­treme heat, dry air, intense light and high wind. They are charac­terised by very strongly formed root system; stunted aerial portion; rolled, folded or otherwise extremely reduced leaves with extra coat­ing of wax on epidermis for preventing water loss, and arrangement for storage of water. Examples: Cacti, Opuntia (B. Fanimansha).

Halophytes grow in sea-shore or saline marshes where absorption of water becomes difficult due to preponderance of salt. A special type of vegetation of low forest called mangrove is found in Sundarbans. Stilt roots for extra support, special aerial roots for absorption of oxygen, cymose branching and peculiar germination called vivi-pary are characteristic features.

Examples – Heritiera (B. Sundri), Ceriops (B. Goran).

According to the nature of stems plants can be put into a number of groups. Some of them have strong stems and so they can stand erect. The erect plants may again be un-branched ones, as in palms; with solid nodes and hollow internodes, as in bamboos; and also with a number of branches forming a spreading crown, as in banyan, mango.

Plants with weak stems cannot naturally maintain upright position. They either creep on the soil surface, as in Dub grass (B. Durba) and sweet potato (B. Ranga Aloo); or climb round a support by twining around it, as in Clitoria (B. Aparajita). Some of them have special sensitive organs for climbing called tendrils, as in Passion-flower (B. Jhumka Lata) and Gourd (B. Kumro).