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.
The organisms in the plant kingdom were classified into divisions or phyla according to structural features.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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