classification and general characteristics of plants

CLASSIFICATION AND GENERAL

CHARACTERISTICS OF PLANTS

Course Section Overview

Classification of Plants

General characteristics and structure of:

• Algae

• Bryophytes

• Pteridophytes

• Gymnosperms

• Angiosperms

Classification of Plants

Two (2) major divisions:

The Cryptogams: Flowerless, seedless plants. They

form three main groups namely, Thallophyta, Bryophyta

and Pteridophyta

The Phanerogams: Flowering plants composed of two

main groups namely Gymnosperms and Angiosperms

Cryptogams: Thallophyta

Plants not forming embryos and do not have a distinct

differentiated plant body form. One of the major sub-divisions

within this group are the Algae

Sub-division Algae: They are characterized by the following:

They are autotrophs i.e. they are chlorophyll bearing organisms

The thalloid body form is simple and not well differentiated. Even

complex thalli lack vascular tissue and epidermis with stomata

The form and size of algae are variable. Chlamydomonas is a

microscopic unicellular algae. Volvox is colonial in form. Ulothrix

and Spirogyra are filamentous in appearance


The sex organs are one-celled; when multicellular, each cell is

fertile

There is no embryo formation after gametic union

All algae are predominantly aquatic in habit, excepting a few

species

They are further classified as blue-green algae, euglenoids,

diatoms, green algae, brown algae and red algae. Red and

brown algae are classified based on the dominant presence of

accessory photosynthetic pigments compared to the chlorophyll

pigment

Cryptogams: Bryophyta

Three sub-divisions exist in this group namely Liverworts (Riccia,

Marchantia), Hornworts (Anthoceros) and Mosses (Sphagnum,

Funaria, Polytrichum)

They are generally characterized by the following:

They are typically small, simple plants with poorly

developed/absent strengthening and conducting tissues

They live mainly in damp, shady places (water and mineral salts

are absorbed by the whole plant surface including rhizoids)


No true stems, roots and leaves; the gametophyte is anchored by

thin filamentous rhizoids. The rhizoids are tiny, slender, absorptive

organs that resemble the roots of higher plants

Plant surface lacks cuticle, or possesses only a delicate one

Sporophyte is attached to, and dependent upon the gametophyte

for its nutrition

Spores are produced in a spore capsule on the end of a slender

stalk (seta) above the gametophyte

Cryptogams: Pteridophyta

Four sub-divisions exist in this group namely psilotophytes(Psilotum), lycophytes (Lycopodium), horsetails (Equisetum) andpterophytes or ferns (Pteris, Polypodium)

They are generally characterized by the following:

They are the highest group of cryptogams, having specialized tissue for the conduction of water and other substances from one part of the plant body to another

They are well differentiated into stems only in the primitive forms to roots, stems and leaves (microphylls and megaphylls) in the more advanced forms


They all produce spores, some groups producing only one type of spore (homosporous), while other sub-groups produce different kinds of spores (heterosporous)

They possess distinct multicellular sex organs, the antheridia and archegonia

They exhibit alternation of heteromorphic generations, in which sporophyte is dominant and free living

They all possess motile sperm, and the presence of water is required for fertilization

Phanerogams

These are also known as the seed bearing plants

(Spermatophyta), which form embryos and constitute the greatest

diversity of plants as known within the Plant Kingdom today

The dominant plant body is the sporophyte, which is well

differentiated into true stem, leaves and roots

They also have a well developed vascular system throughout the

body

There are two (2) major sub-divisions within this group, viz. the

Gymnosperms and the Angiosperms

Phanerogams: Gymnosperms

Sub-division Gymnosperms: They are characterized by the

following:

They bear naked seeds and are usually perennial, evergreen and

woody

They mostly include middle sized or tall trees and shrubs and

number an estimated 70 genera with 725 species. There are no

herbs or climbers

Sporangia are formed over modified leaf-like structures called

sporophylls


There are two types of sporophylls: megasporophyll, which

bears the megasporangium, that produces the ovule (female

gametophyte) and, microsporophyll which bears the

microsporangium (pollen sac). It produces the male gamete (pollen

grain)

The female gametophyte of gymnosperms produce several

archegonia. Thus more than one egg may be fertilized, and

several embryos (may) begin to develop within a single ovule –

known as polyembryony


Water is not required as medium of transport of the sperm to egg

Common examples include pines (Pinus), firs (Abies), larches

(Larix), spruces (Picea), Atlantic cedars (Cedrus atlantica), cycads,

Gingko, etc.

Phanerogams: Angiosperms

Sub-division Angiosperms: Angiosperms are the true floweringplants and are the largest division of photosynthetic organisms onEarth. They are further sub-divided into the Dicotyledons andMonocotyledons

The general features of this group includes the following:

Production of flowers in which sporangia, spores and seeds develop

They exhibit a vast variety of body forms, ranging from herbaceous to woody species

Their life cycle modes range from annual, biennial to perennial

Phanerogams: Angiosperms

A wide range of pollination methods are common among

angiosperms involving agents such as water, wind, insects, animals

and birds

Ovules are protected by carpels in angiosperms

The distinctive phenomenon of double fertilization occurs only in

angiosperms

Seeds are enclosed in an ovary. After fertilization, the ovary

develops into a fruit

Comparison of major Angiosperm sub-divisions

20

Structural components Dicotyledons Monocotyledons

I. Leaf morphology Net-like pattern of veins

(reticulate venation)

Veins are parallel (Parallel

venation)

II. Stem anatomy Ring of vascular bundles Vascular bundles scattered

III. Seed morphology Embryo has two

cotyledons (seed leaves)

Embryo has one cotyledon

IV. Flowers Parts mainly in fours

and fives

Parts usually in threes

V. Examples Rose, dandelion, beans,

cactus, buttercup, etc.

Grasses, lilies, irises,

orchids, palms

classification and general characteristics of plants

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