Download Topic 1 Plant morphology

Topic 1
Plant morphology
1.1 Overview
Plant morphology is the study of those external features of plants used for
recognition and classification. That is, it is a collection of words which allow
you to describe what the plant looks like.
In order to recognise plants, you need to become better acquainted with
terminology which will allow you to describe and documents plant parts such
as leaves. The words used are part of the universal botanical language that
you are starting to learn and these words are understood by all botanists and
plants people world wide.
Consider this, you have an unknown plant and you wish to determine if it is a
plant you want to keep, you may want to know when it will flower or how
large it will grow. How do you determine what the plant is, that is, what is its
botanical name?
There are many good plant recognition and identification books around,
many of them have very accurate descriptions of plants and many have
wonderful clear photographs. Therefore, for plant recognition to be accurate,
and so you can compare the plant you have in front of you to the description
in a textbook, you need to be familiar with the botanical jargon which is
associated with this science of plant recognition.
The main external features that are described are:



leaves
o
shape
o
arrangement
o
attachment
o
apex, base, margin
flowers
fruit.
o
shape
o
arrangement on the plant (inflorescence)
1.2 Typical Plants
We can say that a typical flowering plant is composed of:

a shoot system consisting of stems bearing leaves, flowers and fruit;

a root system.
Table 1 - Main functions of the five plant organs of a typical flowering plant.
Organ
Function
roots
anchoring plants in the soil
absorbing water and nutrients from the soil
storage of some food substances
a means of vegetative propagation
stems
supporting leaves, flowers and fruits
providing a pathway for movement of substances between
the roots and the leaves (translocation)
storage of food substances
photosynthesis within herbaceous stems
a means of vegetative propagation
leaves
manufacture of food substances by the process of
photosynthesis for use by all partsof the plant
evaporation of water from leaf surface (transpiration)
allowing more water to enter the roots
exchange of the gases, carbon dioxide and oxygen,
between plant and atmosphere
storage of food substances
a means of vegetative propagation
aesthetic value
Organ
Function
flowers
production of seed as a result of pollination and
fertilisation
aesthetic value
fruit
protection of seed
help in dispersal of seeds
1.3 Monocotyledons and
Dicotyledons
This group of plants in Class Angiospermae.is divided into two sub-classes:

Monocotyledonae (called monocotyledons or monocots). Examples:
grasses, palms, orchids, lilies.

Dicotyledonae (called dicotyledons or dicots). Examples: roses,
petunias, Prunus spp., Eucalypts, Banksias.
The table below lists the specific differences between these two groups of
flowering plants.
Table 2 - Differences between Monocotyledons and dicotyledons.
Embryo
Monocotyledons
Dicotyledons
One seed leaf
Two seed
(cotyledon)
leaves
(cotyledons)
Growth
Mostly herbaceous, few absorbent
form
Roots
Herbaceous or woody. Herbs, shrubs,
trees
The primary
The primary
root is soon
root persists
replaced by
and becomes
adventitious
a strong
rooots which
taproot with
form a fibrous
smaller
root system
secondary roots. This forms a taproot
system
Vascular
Numerous
1 ring of
system
scattered
vascular
vascular
bundles, stem
bundles; few
differentiating
with
into cortex and
sedcondary
pith;
thickening
secondary thickening common
Monocotyledons
Dicotyledons
Leaf
Parallel
Network
venation
venation
venation
Almost always
Margin varied
entire
Flowers
Floral parts
Floral parts
usually in
usually in
threes or
fours or fives,
multiples of
or multiples of
three
4 or 5
Typical Dicotyledon Plant
The figure below shows the basic organs of a ‘typical’ dicotyledon flowering
plant and their main functions.
Figure 1 - Main function of the plant organs of a ‘typical’ dicotyledon flowering
plant.
Typical Monocotyledon Plant - Grass
Figure 2 - Plant organs of a ‘typical’ grass (monocotyledon) plant.
Plant growth patterns
When plants grow from seed the first soft growth is herbaceous and is called
primary growth. At this stage the roots and shoots are elongating, side
branches of both may develop, but there is no woodiness. Diameters remain
relatively thin. All annual plants show this stage of growth. Plants which do
become woody will also show this in their early development; usually the first
wood is not produced until the end of the first growing season.
Secondary growth, or woody growth is not seen in monocotyledons, and is
only seen in some dicotyledons. All Gymnosperms show woody
development.
Plants that develop secondary or woody growth are trees, shrubs and some
climbers. There is an increase in diameter in both the trunk and the roots
that continues for the life of the plant, which is a