CONCEPT OF SPECIES
Species is the basic and smallest
unit of taxonomy. The definition of species has long been a matter of great
discussion and controversy among biologists. Mayer (1957) and Beaudry (1960)
recognized two classes of species – Taxonomic
Species Concept and
Biological
Species Concept.
1. Taxonomic Species Concept:- This type of
species is the orthodox, classical typological, morphological,
morpho-geographical concept adopted until upto 1930s.
By
the use of correlated morphological discontinuation in a number of features,
groups of individuals can be clearly distinguished as taxonomic species.
According to Du Rietz (1930) ‘the species is the smallest natural
populations permanently separated from each other by a distinct continuity’.
It is intended as a general applicable concept and takes into account all
evidences, morphological, geographical, etc. But the species must be delimited
by morphological characters. Taxonomic species are recognized by the type
method or type concept.
2. Biological Species Concept:- This type of species is the most
modern concept of species including the biosystematics, genetical, etc.
It is the most accepted definition
of species in higher plants. Grant (1971) defined biological species as ‘the
reproductively isolated system of breeding populations’. Mayr (1969)
defined it as ‘groups of interbreeding natural populations that are reproductively
isolated from other such groups’. Dobzhansky (1935) defined species in
terms of interbreeding and reproductive isolation.
According to Simpson (1943) ‘a
genetic species is a group of organisms so constituted and so situated in
nature that a hereditary character of any one of these organisms may be
transmitted to a descendant of any other’. Dobzhansky (1950) defines
species as ‘the largest and most inclusive reproductive community of sexual and
cross fertilizing individuals which share a common gene pool’.
CONCEPT OF GENUS
Genus
(plural – genera) is the next higher
taxon after species and composed of one or more species. The species
constituting the genus must have more similarities than differences among
themselves. For example – Solanum is
a genus which has a number of species – S.
tuberosum, S. melongena, S. khasianum, S. torvum, etc.
CONCEPT OF FAMILY
Family is the next higher taxon
after genus and composed of one or more genera. The genera constituting the
family must have more similarities than differences among themselves. According
to “International Code of Botanical Nomenclature” rule the name of the family
is a plural adjective used as a substantive. It is formed by adding the suffix
‘aceae’ to the type genus. For example – the family Malvaceae is formed after
its type genus ‘Malva’ (Malva+aceae = Malvaceae), likewise
Rosaceae (Rosa+aceae = Rosaceae),
Magnoliaceae (Magnolia+aceae =
Magnoliaceae), etc.
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