The system of
classification of plants has existed from centuries. It began to be formally
known during the era of Carlous Linnaeous when he first published the book
about classification of plants and a few years later published book of
classification of animals. The classification system proposed by Linnaeous is
knows today as conventional system.
I)
THALLOPHYTA
These are the simplest
organisms which had cell walls and lack structures like roots, stems and
leaves. They include bacteria, fungi and algae. The most renowned among these
are mushrooms and nitrogen fixing bacteria. And many are notorious plant
pathogens causing serious diseases of plants like rusts and smuts.
II)
BRYOPHYTA
These are mosses,
liverworts and hornworts which lack true roots and flowers. These species are ecologically
very important in the tropics and forest ecosystems.
III)
PTERIDOPHYTA
These are higher plants
having vascular systems and true leaves, stems and roots. They do not have
flower and fruit formation and hence reproduce through spores. For example,
ferns, club mosses, horsetails etc. are commonly found in tropics and forest
ecosystems and they have agronomic use as ornamentals only.
IV)
SPERMATOPHYTA
These are the higher
plants which have true roots, stems, leaves and vascular tissues and reproduce
through seeds and bear true flowers. This division is further divided into two;
a)
GYMNOSPERMS
They are also called “naked
seeded” plants because their seeds are not produced inside the fruits rather
are lying on the structures called “cones”. For example, pine, fir, and cedar. They
have significance as ornamental plants in modern times and also an essential
part of alpine and forests.
b)
ANGIOSPERMS
They produces seeds
inside true fruits and these are highly adaptable plants and found almost in
every ecosystem. All the cultivated crops belong to angiosperms. They have
further 2 categories based on the number of cotyledons present inside their
seeds as;
i)
MONOCOTS (aka Monocotyledons)
They have single
cotyledon in their seed. Their germination is hypogeal and most important
cereals and fodders belong to this group, for example, wheat, rice, maize,
barley, sorghum belonging to the family poaceae.
ii)
DICOTS (aka DICOTYLEDONS)
They have two
cotyledons in their seeds and they are most advanced plants. Their germination
is epigeal. The plants are broad leaved. Many of them are economically
important to man for either food, fiber or other purposes. For example,
cucurbits, soybean, pulses, tobacco and cotton.
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