Structural Information in Phytosystematics: A Molecular Perspective
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Class MS
Semester II
Molecular Advances in Phytosystematics
Instructor: Dr. ARUSA AFTAB
Department of Botany
LAHORE COLLEGE FOR WOMEN
UNIVERSITY LAHORE
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Taxonomic characters are the taxonomic
attributes that can be used to provide the
evidence from which relationships
(the phylogeny) between taxa are
inferred.
Kinds of structural taxonomic characters
include: vegetative and reproductive
characters, morphological and anatomical
characters, mature and developmental
characters.
Modern taxonomists consider that the gross
morphological characters are not always
sufficient to provide means of differentiation in
determining the genetically and evolutionary
relationship between taxa.
Baily (1949) has said, “If a truly natural
classification is to be attained, it must be
based upon the analysis and the
harmonization of evidence from all organs,
tissues and parts.
Morphological characters provide
the framework for taxonomy and
they have been used extensively in
the preparation of classification
systems, diagnostic keys etc.
The morphological characters are
easily observable, to analyse these
characters no need of sophisticated
laboratory arrangements.
A hand lens or dissecting
microscope, or possibly a light
microscope is enough to study these
characters.
Well-knit terminologies are used to
describe variations in morphologies.
It is often argued that exomorphic
characters are less important than
the endomorphic or other
characters.
Morphologist examines structures in
many different plants of the same or
different species, then draws
comparisons and formulates ideas
about similarities.
When structures in different species
are believed to exist and develop as
a result of common,
inherited
genetic
pathways, those
structures are termed homologous
.
For example, the leaves of pine, oak, and
cabbage all look very different, but share
certain basic structures and arrangement of
parts. The homology of leaves is an easy
conclusion to make.
Plant morphology studies plant structure at
a range of scales (smallest scales are ultra
structure and structural features of cells
with the aid of electron microscope and
optical microscope)
At this scale, plant morphology overlaps
with plant anatomy as a field of study.
Anatomical features can be used in
taxonomy for the identification of plants,
establishing genetic relationships and solving
taxonomic disputes.
Anatomical characters are conserved (do not
change) and stable.
Anatomical characters used in plant
systematics are trichomes, stomata and
epidermal features, leaf anatomy, nodal
anatomy, stem anatomy, cambium and wood
anatomy.
For example,
Characters of trichomes
such
as glandular, non- glandular, unicellular,
multicellular, shape and size are used to
compare closely related taxa.
The SEM
features of stomata and epidermis
are used for comparison.
Some families are specific for their stomata
such as:
Anomocytic stomata Ranunculaceae
Anisocytic stomata in Brassicaceae
Paracytic stomata in rubiaceae
Graminaceous stomata in poaceae
The sunken stomata in plants indicates its
xerophytic habitats.
Leaf anatomy
: is extensively used in the
systematics of the cyperaceae family.
Characters of leaf anatomy in plant
taxonomy are:
The gross anatomical structure of the
leaf(dicot and monocot).
Structural variability: features of mesophyll,
bundle sheath, hydathodes, kranz anatomy,
foliar nectaries and glands, oil glands,
stomatal crypts and features of leaf
abscission.
Three different types of nodes based on
anatomical characteristics:
1.
Unilacunar node
: a node with one lacuna of
leaf e.g Nerium, Calotropis.
2.
Trilacunar node
: a node with 3 lacunae or leaf
gaps e.g Azadirachta.
3.
Multilacunar node
: a leaf with many lacunae
or leaf gaps e.g Rumex, Polygonum.
Stem anatomy
include features of epidermis,
hypodermis, distribution of collenchyma,
sclerenchyma, piths, storage region. For
example,
Bicollateral vascular bundules in cucurbitaceae
Anccessory cortical and medullary bundles in
Nyctaginacae
Sclereids
: nature, type and distribution of
sclereids and fibers have taxonomic
significance, For example
Monocot fibers are hard fibers (coir, musa)
Dicot fibers are soft fibers (jute)
Cambium
: formation of secondary cambium,
storied vs non storied cambium.
Wood anatomy
: is used to detect
adulteration in medicinal plants
Features of wood used in systematics are
vessels, wood parenchyma, Ray system,
storied structure
Reproduction in flowering plants involves a
complex series of events, beginning with
floral induction and ending with germination
of seeds.
Characters of reproductive cycle, especially
those of the flower, but also those of
embryology, pollen and other features, are of
great traditional utility in taxonomy.
Certain generalizations can be made with
regards to the characters found to be most
useful in certain taxa, or the level of
conservativeness of certain characters.
For example in Rannanculaceae, the
bracts sepals and petals are important, in
the Asteraceae and poaceae the
inflorescence, bracts and general flower
types and in Fabaceae the stamens and
carpels.
Broad pattern of structure fruits and
seeds is in general a less reliable
taxonomic criterion (superficially similar
fruits or seeds sometimes being found in
only remotely related groups), they are
often of supreme importance.
In such large families as the Brassicaceae
and Apiaceae, for example, the fruits
provide the most useful characters of all,
and they are scarcely less important in
the Rosaceae.
In such families number of special terms
are used to describe variation of the
fruits.
Similarly, seeds are important in certain
families such as caryophyllaceae.
Seed structure produces taxonomic
criteria at all levels of the hierarchy.
In higher plants vegetative characters are
often looked upon a risky evidence, because
there are many cases where superficially
similar morphological characters are found in
quite unrelated plants.
Similar growth- habitat (e.g. cactus-like
plants, broom-like plants, tress) or leaf shapes
(e.g. palmate-lobed, compound pinnate) are
good example.
Many other examples could be given for
example the moss Andreaea, which is similar to
the true mosses vegetatively but to sphagnum on
capsule characters.
Developments is the progression from
earlier to later stages in maturation e.g. a
fertilized egg develops into a mature
tree, its is the process whereby tissues,
organs and whole plants are produced, its
involves growth, morphogenesis (the
acquisition of form and structure), and
differentiation.
So developmental stages are good
criteria in taxonomy.
The life cycle of plants is a good example to
study developmental characters such as
features of sporogenesis, gametogenesis,
fertilization and embryogenesis in flowering
plants.
Mature plant cells can be stimulated under
certain condition to divide and differentiate
again.
This happens when tissues are wounded , as
when branches break or leaves are damaged by
insects.
The plant repair itself by differentiating
parenchyma cells in vicinity of the wound,
making cell like those injured or else
physiologically similar cells
This continuous growth results in:
Two general groups of tissues, primary and
secondary
Two body type, primary and secondary
apical and lateral meristems
Exploring the significance of taxonomic characters in molecular advances of phytosystematics, this class delves into the role of structural attributes in determining relationships between taxa. From considering gross morphological characters to analyzing morphological characters under microscopes, the course emphasizes the importance of detailed observation and classification techniques. By studying variations in morphologies and identifying homologous structures, students gain insights into evolutionary relationships within plant species.
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Presentation Transcript
STRUCTURAL INFORMATION Class MS Semester II Molecular Advances in Phytosystematics Instructor: Dr. ARUSA AFTAB Department of Botany LAHORE COLLEGE FOR WOMEN UNIVERSITY LAHORE
STRUCTURAL INFORMATION
STRUCTURAL INFORMATION Taxonomic characters are the taxonomic attributes that can be used to provide the evidence from (the phylogeny) inferred. Kinds of structural taxonomic characters include: vegetative characters, morphological and anatomical characters, mature and developmental characters. which between relationships taxa are and reproductive
Modern taxonomists consider that the gross morphological characters sufficient to provide means of differentiation in determining the genetically and evolutionary relationship between taxa. Baily (1949) has said, If a truly natural classification is to be attained, it must be based upon the harmonization of evidence from all organs, tissues and parts. are not always analysis and the
MORPHOLOGICAL CHARACTERS Morphological the framework for taxonomy and they have been used extensively in the preparation systems, diagnostic keys etc. The morphological characters are easily observable, to analyse these characters no need of sophisticated laboratory arrangements. characters provide of classification
A microscope, microscope is enough to study these characters. Well-knit terminologies are used to describe variations in morphologies. It is often argued that exomorphic characters are less important than the endomorphic characters. hand lens or or dissecting a possibly light or other
Morphologist examines structures in many different plants of the same or different species, comparisons and formulates ideas about similarities. When structures in different species are believed to exist and develop as a result inherited genetic pathways, those structures are termed homologous. then draws of common,
For example, the leaves of pine, oak, and cabbage all look very different, but share certain basic structures and arrangement of parts. The homology of leaves is an easy conclusion to make. Plant morphology studies plant structure at a range of scales (smallest scales are ultra structure and structural features of cells with the aid of electron microscope and optical microscope) At this scale, plant morphology overlaps with plant anatomy as a field of study.
ANATOMICAL CHARACTERS Anatomical taxonomy for the identification of plants, establishing genetic relationships and solving taxonomic disputes. Anatomical characters are conserved (do not change) and stable. Anatomical characters systematics are trichomes, epidermal features, anatomy, stem anatomy, cambium and wood anatomy. features can be used in used in plant and nodal stomata anatomy, leaf
For example, Characters of trichomes such as glandular, non- multicellular, shape and size are used to compare closely related taxa. The SEM features of stomata and epidermis are used for comparison. Some families are specific for their stomata such as: Anomocytic stomata Ranunculaceae Anisocytic stomata in Brassicaceae Paracytic stomata in rubiaceae Graminaceous stomata in poaceae glandular, unicellular,
The sunken stomata in plants indicates its xerophytic habitats. Leaf anatomy: is extensively used in the systematics of the cyperaceae family. Characters of leaf taxonomy are: The gross anatomical leaf(dicot and monocot). Structural variability: features of mesophyll, bundle sheath, hydathodes, kranz anatomy, foliar nectaries and stomatal crypts and abscission. anatomy in plant structure of the glands, features oil glands, of leaf
Three anatomical characteristics: Unilacunar node: a node with one lacuna of leaf e.g Nerium, Calotropis. Trilacunar node: a node with 3 lacunae or leaf gaps e.g Azadirachta. Multilacunar node: a leaf with many lacunae or leaf gaps e.g Rumex, Polygonum. Stem anatomy include features of epidermis, hypodermis, distribution sclerenchyma, piths, example, Bicollateral vascular bundules in cucurbitaceae Anccessory cortical and medullary bundles in Nyctaginacae different types of nodes based on 1. 2. 3. of collenchyma, region. storage For
Sclereids: nature, type and distribution of sclereids and fibers significance, For example Monocot fibers are hard fibers (coir, musa) Dicot fibers are soft fibers (jute) Cambium: formation of secondary cambium, storied vs non storied cambium. Wood anatomy: adulteration in medicinal plants Features of wood used in systematics are vessels, wood parenchyma, storied structure have taxonomic is used to detect Ray system,
REPRODUCTIVE CHARACTERS Reproduction in flowering plants involves a complex series of events, beginning with floral induction and ending with germination of seeds. Characters of reproductive cycle, especially those of the flower, but also those of embryology, pollen and other features, are of great traditional utility in taxonomy. Certain generalizations can be made with regards to the characters found to be most useful in certain taxa, or the level of conservativeness of certain characters.
For bracts sepals and petals are important, in the Asteraceae inflorescence, bracts and general flower types and in Fabaceae the stamens and carpels. Broad pattern of structure fruits and seeds is in general taxonomic criterion (superficially similar fruits or seeds sometimes being found in only remotely related groups), they are often of supreme importance. example in Rannanculaceae, the and poaceae the a less reliable
In such large families as the Brassicaceae and Apiaceae, for example, the fruits provide the most useful characters of all, and they are scarcely less important in the Rosaceae. In such families number of special terms are used to describe variation of the fruits. Similarly, seeds are important in certain families such as caryophyllaceae. Seed structure produces criteria at all levels of the hierarchy. taxonomic
VEGETATIVE CHARACTERS In higher plants vegetative characters are often looked upon a risky evidence, because there are many cases where superficially similar morphological characters are found in quite unrelated plants. Similar growth- habitat (e.g. cactus-like plants, broom-like plants, tress) or leaf shapes (e.g. palmate-lobed, compound pinnate) are good example.
Many example the moss Andreaea, which is similar to the true mosses vegetatively but to sphagnum on capsule characters. other examples could be given for
DEVELOPMENTAL CHARACTERS Developments is the progression from earlier to later stages in maturation e.g. a fertilized egg develops into a mature tree, its is the process whereby tissues, organs and whole plants are produced, its involves growth, acquisition of form and structure), and differentiation. So developmental criteria in taxonomy. morphogenesis (the stages are good
The life cycle of plants is a good example to study developmental features of sporogenesis, fertilization and embryogenesis in flowering plants. characters such as gametogenesis,
MATURE CHARACTERS Mature plant cells can be stimulated under certain condition to divide and differentiate again. This happens when tissues are wounded , as when branches break or leaves are damaged by insects. The plant repair itself parenchyma cells in vicinity of the wound, making cell like those physiologically similar cells This continuous growth results in: Two general groups of tissues, primary and secondary Two body type, primary and secondary apical and lateral meristems by differentiating injured or else
