Biological Species Concept.
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Biological Species Concept.
The biological species concept is that individuals of different species
cannot interbreed to produce fertile offspring.
As many plants hybridize readily it is not very useful to strictly apply
the biological species concept to botanical classification.
Reproductive systems in plants range from dioecy (dioecious is a Greek
term for ‘two houses)with separate male and female plants, to apomixis
which is asexual reproduction and will include formation of seeds without
fertilization.
Apomicticraces
can be constant enough to be given specific rank.
Purposes of Classification
The main purpose of classification is to enable one to sort out and
understand the diverse group organisms in nature and group them into
recognizable categories.
Classification is a process, which human beings have carried out in the
past, will carry it today and will be carrying it out in the future.
For example:
People in various parts of the world identify groups of animals thay they
consider aggressive. These could be Leopard, Tigers, Lions , etc
which are grouped into the Cat Family.
People in various parts of the world have domesticated various speicies
of plants for food.
For example:
Common Wheat (Triticum aestivum ( in the Middle East,
Barley (Hordeum vulgare) in the Middle East adn Ethiopia
Maize/Corn (Zea mays ) in Central America
Sorghum , Broom Corn, Guiner Corn (Sorghum bicolor) in the Sudanian
Region
Teff ( Eragrostis tef) in Ethiopia
All these belong to the grass family _ Gramineae/Poacea
In various cultures other groups of plants have been domesticated.
Potato (Solanum tuberosum) in South America (the Andes)
Tomato (Lycopersicon esculentum)
Pepper (Capsicum spp.) South America
These species belong to the Family Solanaceae
Tuber Crops
Cassava ( Manihot esculenta) in the Family Euphorbiaceae
Enset(Ensete ventricosum) in the family Musaceae
Banana (Musa acuminata) in the family Musaceae
In order to appreciate the importance of classification, one only need to
know the estimated number of organisms in the world.
See Table 1 below. If organisms were not grouped into larger and higher
categories, it would have been difficult for anyone scientist to recognize
even a tiny portion of the diversity
Taxonomists
should lay the bases, principles, procedures and rules in order to
classify organisms with the following objectives in mind.
•
to provide a convenient
method of identifying, naming and describing organisms
•
To construct classes about which we can make generalization.
•
to provide a classification scheme which attempts to express natural or
phylogenetic relationship depending on the purpose
•
To provide an inventory of animals or plant taxa to provide information
to national, regional, worldwide flora and fauna
•
to provide an understanding of evolutionary processes and
relationships.
According to Simpson (1961:23), the theoretical bases for
hierarchical classification
involves two operating principles.
- The primary operation (conceptual ) is the aggregation of
organisms into taxa of the lowest rank
2.The secondary operations consist simply in aggregating the previous
taxa into
higher more inclusive category and rank, and the process continues.
Thus it follows,
accordidng to Simpson (1961:25),
the basis for classification must
Be the relationships among organisms, but relationships in the wider
sense
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Are of many kinds.Therefore, the logical conclusion from the above
statement is that, it is not only
Possible to have different classifications, but different bases for the
classifications.
The most important taxonomic level is the species. Below species level,
subspecies, varieties, forms, races and cultivars can be recognized.
Species are grouped into genera (singular = genus), which in turn are
grouped into various higher taxonomic ranks the most important of which
the family .
For example the kidney or common bean, scientifically known as Phaseolus
vulgaris can be classified as follows.
Classification of common bena
Class: Angiospermae (Magnoliopsida)
Subclass: Dicotyledonae
Superorder: Rosidae
Order: Fabales
Family: Fabaceae (Leguminosae)
Subfamily: Papilionoideea
Tribe: Phaseolinae
Subtribe: Phaseolinae
Genus: Phaseolus
Variety: Phaseolus vulgaris var humilis
Cultivar: Phaseolus vulgaris ‘Canadian wonder
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