2-Species concept.pdf for botany bs 5th samester

Species' topic

1. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

1
CHAPTER 2
CONCEPT OF SPECIES
1. What is a species?
2. Taxonomic species.
3. Biological species.
4. Micro and macro species.
5. Species aggregate
6. Infra specific categories.

What is a species?
A species concept is a way of defining a species, and a recent reviewer found
24 different species concepts that have been proposed over the past century. The most
famous, and the one that most biologists use today, is the
biological species
concept
, which states that species are groups of actually or potentially interbreeding
populations, which are reproductively isolated from other such groups. In other
words, speciation is the evolution of reproductive isolation between two groups.
Operationally, this definition works well for most animals. However, it has limitations:
it does not always work with plants, and it cannot be applied to extinct species (e.g.
fossils) or asexually reproducing species (e.g. bacteria).
Species is a group of individuals or population living together at the same time
and same space, and can interbreed among themselves and produce fertile offspring.
There are following types of species concepts:
1. Morphological species concept or taxonomic species
concept:
It is oldest view and still held by majority of taxonomists. In morphological
species concept individuals of the same population or individuals of same species have
morphological similarities.
OR
Species are the smallest natural populations permanently separated from each
other by a distinct discontinuity in the series of biotype (Du Rietz, 1930; Bisby and
Coddington, 1995).
2. Biological species concept:
A species is a group of interbreeding natural populations unable to successfully
mate or reproduce with other such groups, and which occupies a specific niche in nature
(Mayr, 1982; Bisby and Coddington, 1995).

2. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

2
In biological species the taxonomists neglect morphology but they consider
reproductive barrier. If species are interfertile then they are combined into one species.
But which are not interfertile, they are regarded as different species (Separate species).
3. Phylogenetic species concept:
A species is the smallest group of organisms that is diagnosably [that is,
identifiably] distinct from other such clusters and within which there is a parental
pattern of ancestry and descent (Cracraft, 1983; Bisby and Coddington, 1995).
In higher vascular plants especially in angiosperms, the evolution is a continuous
process. The most important characters in evolution are:
1. Mutation
2. Recombination
3. Selection
4. Isolation
If these groups of plants are not isolated from each other, then these are one
species. In certain plants mutations lead to variations in chromosomal number within
same population. These plants may have diploid, tetraploid and even octaploid
individuals. These are reproductively isolated; hence biological species have different
gene pools i.e., diploid, tetraploid, octaploid. But if these gene pools are not
accompanied with morphological difference, they can not be accepted as morphological
or taxonomic species. They are merely termed as cytological races or cytodemes. This
example clearly shows that biological species cannot be equated i.e., that biological
species and morphotaxonomic species cannot be equated or equal and most of the
morphotaxonomists are of the view that biosystematists, which are responsible for
biological species, must have their own term.
Microspecies or Satellite species
The middle region of the earth is more suitable for growth of population while in
periphery region there is extreme of environmental conditions. So group of plants start
isolating from one another due to intervening of unfavorable environmental conditions.
After many years they become differentiated from middle species and thus new
species are produced on the peripheral regions. Small group of plants in such peripheral
regions is known as
microspecies or satellite species.
These small populations develop favorable variations by undergoing mutation,
recombination, selection and isolation. These smaller populations of the same at the
periphery of distributional range are called as
microspecies or satellite species.
These species become different from parent species.

3. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

3
The classic example of very long geographical isolation is that of Platanus
species. There are two species of
Platanus.
Platanus orientalis
Platanus occidentalis
P. orientalis
is found in Eastern Mediterranean region of Turkey.
P. occidentalis is found in Eastern United States (a distance of thousand miles from
eastern Mediterranean region) The above two species of
Platanus live in habitats,
where ecology differ by vary low temperature and snow fall. Both these species are
called
vicarious (Closely related allopatric species are called as Vicarious) . So they
are interfertile.
These two species are fully fertile (interfertile) with on another although these
species are geographically isolated for millions of years. It means in these species
geographical isolation could not produce or induce reproductive isolation.
Second example of microspecies is
Catalpha ovata
Catalpha bignonioides
.
C. ovata is found in China while C. bignonioides is found in United States
and they have similar habitats. Very high temperature found at high altitude but they are
highly interfertile with one another. Although there is very long distance isolation but
still there is no genetic isolation.
In botany,
apomixis is asexual reproduction, without fertilization. Apomixis
mainly occurs in two forms: In
agamogenesis, the embryo arises from an unfertilized
egg via a modified meiosis. In
agamospermy (also called apogamy), a nucellar
embryo is formed from the surrounding embryo sac tissue. Apomictically produced
seeds are genetically identical to the parent plant. As apomictic plants are genetically
identical from one generation to the next, each has the characters of a true species,
maintaining distinctions from other congeneric apomicts, while having much smaller
differences than is normal between species of most genera. They are therefore often
called
microspecies. In some genera, it is possible to identify and name hundreds or
even thousands of microspecies, which may be grouped together as
aggregate
species
, typically listed in Floras with the convention " Genus species agg." (e.g., the
bramble,
Rubus fruticosus agg.). Good examples of apomixis can be found in the

4. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

4
genera Crataegus (hawthorns), Sorbus (rowans and whitebeams ), Rubus (brambles
or blackberries), Hieracium (hawkweeds) and
Taraxacum (dandelions). Species aggregate (Supraspecific Ranks)
In current taxonomic literature we often come across citation such as Euphrasia
officinalis
(sensu lato). The term “sensu lato” indicates that it is an aggregate of
several species including
E. micrantus Rei. and E. scottica Wettst. It is a compound
species, which cannot be treated as a single species or individual species. It becomes a
Supraspecific taxon that includes more than one species. During 1950,s to 1960,s there
was a tendency to describe such groups as species aggregates which has its roots in
Engler’s species
Collectiva. This concept is a device by which we can conveniently
grouped together several closely related species and can be spared the ordeal of
memorizing so many names. The constituent species are termed as
segregate.
Similar treatment of closely related species under what are called
supraspecies
has been suggested by Mayer in 1931 and Cane in 1954. But the supraspecies concept
unlike that of the aggregate is an evolutionary concept, where the emphasis is on the
monophyletic origin of the constituent species.
A
supraspecies is defined as “A monophyletic group of entirely or essentially
allopatric species that are to distinct to be included in the single species”.
Amadon in 1966 amended this definition slightly as “ A group of entirely or
essentially allopatric taxa that were once races of single species but which now achieved
species status.”
(
Allopatric species: The formation of new species over a length of time, by the
geographical isolation of groups of the common ancestor e.g., by the mountain range)
Infra specific categories
The three most widely used infraspecific categories are subspecies, botanical
variety (both applicable to wild plants or wild plants brought into cultivation), and
cultivar group (for groups of man- made cultivars). The phrase "botanical variety" is
used here to avoid confusion with the cultivar.
Other infraspecific ranks permitted by the ICBN but rarely used are subvar.
(Botanical subvariety, beneath the botanical variety), forma (form, beneath the botanical
subvariety) and subforma (subform, beneath the form).
Variations within the species, which occur in nature, are classified into infra-
specific taxa - mostly
subspecies, varietas (= botanical variety), and forma (form).

5. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

5
Variations, which are selected in cultivation and deliberately propagated, are called
cultivated varieties (cultivar for short), or simply varieties.
REMEMBER: Variety or cultivar is not the same as varietas or botanical variety.
Species (the genus name and the specific epithet together make up the scientific name
of a species)
Subspecies (a subdivision of a species; many species are not divided into subspecies)
Variety (many subspecies are not divided into varieties; sometimes varieties are
treated in the same sense as subspecies; in other instances the subspecies category is
used for grouping varieties within a species)
Form (used for minor differences such as flower color)
• Subspecies: (Group of plants geographically isolated exhibiting distinctive
morphological features selected by environmental pressures through sexual
reproduction yet not sufficiently distinct according to taxonomic judgment to be
classified as a species. Criteria are commonly geographical separation of groups plus a
combination of morphological characters).
• Variety: (Group of plants exhibiting distinctive morphological features selected by
environmental pressures through sexual reproduction yet not sufficiently distinct
according to taxonomic judgment to be classified as a subspecies or species. Criteria are
commonly a combination of morphological characters).
• Forma: (Lowest subdivision of a species ranking, used mainly to indicate a single
trait that occasionally occurs in a population. Most taxonomists no longer use this rank).
Cultivar: A plant selected by humans for unique morphological or physiological
traits and usually propagated asexually to maintain those traits.
Rules of nomenclature for infra specific categories:
If the species has infraspecific categories e.g. in Asparagus, which has two
subspecies, they are written as:
Asparagus officinalis subsp. Prostrates
Asparagus officinalis subsp. Officinalis
The rank of the infraspecific category must always be stated i.e., is it subspecies,
varietas, or form etc?
[Abbreviated as subsp. (or ssp.), var. and f. The plurals are subspp. (or sspp.), vars.,
and ff.]
Hence in creeping willow there are a number of botanical varieties which are written
as so:

6. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

6
Salix repens var. repens
Salix repens var. fusca
Salix repens var. argentea
Selected forms of plants which are grown in gardens and which do not occur in the wild
are called
cultivars or cultivated varieties or simply varieties. Until recently their names were written in two ways, both of which were correct, and
will be found in older literature:
Geranium endressii cv. A.T. Johnson or
Geranium endressii ‘A. T. Johnson’
Ipheion uniflora cv. Wisley Blue or
Ipheion uniflora ‘Wisley Blue’
However, a recent change in the Rules means that you must from now on only quote
cultivar names within single inverted commas i.e.
Geranium endressii ‘A. T.
Johnson’ and
Ipheion uniflora ‘Wisley Blue’, etc. Do not use the abbreviation cv.
Cultivar names must begin with capital letters. Modern cultivar names are now always
in a modern language, not Latin, and are not written in italics like the Latin names.
(But old cultivar names invented before these rules may be in Latin form; they are still
valid. Old common Latin cultivar names are ‘alba’ for white-flowered varieties)
a) Subspecies
The full name of a subspecies is composed of three name parts plus the
subspecies marker "subsp." plus the species author string and the subspecies author
string. The name parts are: genus name, species epithet, and subspecies epithet. An
exception is that where the subspecies epithet is the same as the species epithet (an
autonym), there is no subspecies author.
Pisum sativum L. subsp. arvense Poir.
Pisum Genus name
sativum Species epithet
L. Species author string
subsp. Infraspecific marker - subspecies
arvense Infraspecific epithet
Poir. Infraspecific author string

b) Botanical Variety (Subvariety, Forma etc.)

7. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

7
The full name of a botanical variety is composed of three name parts plus the
variety marker "var." plus the species author string and the variety author string. An
exception is that where the variety epithet is the same as the species epithet (an
autonym), there is no variety author.

Vicia johannis Tamamsch. var. procumbens H.I.Schäf.
Vicia Genus name
johannis Species epithet
Tamamsch. Species author string
var. Infraspecific marker - botanical variety
procumbens Infraspecific epithet
H.I.Schäf. Infraspecific author string

It is correct and precise to reduce a name that gives several infraspecific categories to
only one infraspecific category. Thus a botanical variety or forma name given as a
quadrinomial or pentanomial should be entered as a trinomial using only the lowest
infraspecific category of those given.
For:
Heracleum sphondylium subsp. sibiricum var. lecokii
Enter:
Heracleum sphondylium var. lecokii
A similar trinomial structure is used for subvariety, forma and subforma.
c) Cultivar group
The full name of each cultivar group is composed of three name parts (genus
name, species epithet and cultivar group name) plus the cultivar group marker and the
species author. However, in some cases where the cultivar group is of interspecific or
uncertain origin, it is composed of just two parts, the genus name and cultivar group
name. (The "cultivar group" is widely used as the principal recognizable grouping of
cultivars within plant species where there are many cultivars. However this is an
informal usage and the present ICNCP refers only to "groups"). There is no author
string for a cultivar group name.
Vicia faba L. Longpod Group
Vicia Genus name
faba Species epithet
L. Species author string
Longpod cultivar group name
Group cultivar group marker
d) Cultivar:

8. PLANT SYSTEMATICS, BIODIVERSITY & CONSERVATION
DR. ZAFAR ULLAH ZAFAR

8
The full name of a cultivar can have three different forms. The commonest is
three name parts (genus name, species epithet, and cultivar name) plus the cultivar
marker and the species author string.
Vicia faba L. cv. Aquadulce
Vicia Genus name
faba Species epithet
L. Species author string
cv. Cultivar marker
Aquadulce Cultivar name
An alternative presentation of the same name is to use single quotation marks as
the cultivar marker, so that the name would appear in printout as follows:
Vicia faba L. 'Aquadulce'