Download Leaves

WHMF121
Session Nine
Plant Morphology Part IV
Leaves
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Photograph with permission David Stelfox
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Topic Overview
o Leaf anatomy (lamina, petiole, axis, midrib etc)
o Leaf characteristics (structure,
attachment, arrangement, shape,
venation and margin).
o The functions of leaves
o Leaf modifications (tendrils, spines,
bracts)
o The theory behind photosynthesis
The characteristic leaf of Ginkgo
biloba. Notice the species name
identifies the bilobate leaf
shape.
Image credit: Wikipedia, viewed 14 January 2014
http://commons.wikimedia.org/wiki/File:Ginkgo_biloba_scanned_leaf.jpg
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Leaves
o Leaves consist of a leaf blade or lamina, which is often,
but not always, carried on a stem called the petiole.
o The petiole may extend along the centre of the leaf
forming the mid-rib.
o Leaves grow at the nodes
of a stem.
Image credit: Wikipedia, viewed 14 January 2014
http://commons.wikimedia.org/wiki/File:Maple_Leaves.jpg
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Leaves
o The angle formed by the
leaf and the stem is the leaf
axil.
o Axillary buds are found in
leaf axils.
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Leaves
o Leaves have a range of
characteristics which can be
used to describe them.
o Comparing leaf
characteristics is one of the
ways that plant species and
plant families can be
distinguished from each
other.
Image credit: Science and Plants for School, , viewed 14 January 2014
http://www.flickr.com/Images/71183136@N08/7128074957/in/Imagestream/
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Leaf Characteristics
o Leaf structure: Leaves are said to be either simple or
compound in structure. This refers to the lamina of the leaf
o Attachment: Refers to how the leaf joins the stem
o Arrangement: Leaves grow on stems in distinctive patterns
o Shape: Refers to the shape of the lamina of leaf or leaflets
o Venation: The pattern of the veins on a leaf
o Margin: The leaf margin is the edge of the lamina
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Leaf Structure
Image credit: Wikipedia, , viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Silver_maple_leaf.jpg
Image credit: Wikipedia, , viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Fern_detail.jpg
Leaves are said to be either simple or compound in structure
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Leaf Structure
Leaves are described as simple or compound
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Leaf Structure
o Simple leaves have one continuous
lamina.
o Leaves of Taraxacum officinale
(Dandelion) see picture opposite,
Mentha piperita (Peppermint) and
Galium aparine (Clivers) are simple
leaves.
Image credit: Wikipedia, viewed 14 January 2014
http://commons.wikimedia.org/wiki/File:Dandelion-leaf.jpg
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Leaf Structure
o Compound leaves have the
lamina divided into leaflets.
o When the leaflets grow from a
continuation of the petiole
(called the rachis in compound
leaves) the leaf is said to be
pinnate (the leaflets are called
pinnae) e.g. Sambucus nigra
(Elder)
Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/Leaf
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Leaf Structure
o In some compound leaves the
pinnae themselves are divided
into smaller leaflets called
pinnules.
Simple Pinnate Leaf
Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Fern_frond_pinnate.jpg
o These are called bipinnate
leaves
Binnate Leaf Image credit: Tatiana Gerus, viewed 14 January 2014
http://www.flickr.com/Images/tgerus/6350521762/
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Leaf Structure
o In a compound leaf if the pinnae grow from the end of the
petiole it is called palmate (when there is more than three
leaflets).
o e.g. Aesculus hippocastanum (Horsechestnut) or trifoliate
as in clover or Trifolium pratense (Red clover).
o In some cases it is difficult to tell whether there is one
compound leaf or many small, simple leaves.
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Leaf Structure
How do you know if a leaf is simple or compound?
o Look at the leaf axil and axillary bud.
o The leaf axil is the angle formed between the leaf and
the stem.
o Each leaf has one axillary bud in the axil.
o The axillary bud therefore defines the leaf.
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Leaf Attachment
Leaf attachment refers to how the leaf joins the stem and
may be:
1. Articulate: when a definite joint can be seen where the
leaf or petiole are attached to the stem. e.g. Mentha
piperita (peppermint), Sambucus nigra (elderflower)
2. Petiolate: if a petiole connects the leaf to the stem e.g.
Mentha piperita, Sambucus nigra
3. Sessile: if there is no petiole and leaves join straight on
to the stem. e.g. Elymus repens (couch grass) and
Galium aparine (cleavers).
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Leaf Attachment
o Some special leaf attachments include:
1. Sheathing: where the bases of the petioles wrap around
the stem e.g. Petroselinum crispum (parsley), many
grasses.
2. Decurrent: where the lamina extends onto the side of
the stem e.g. Symphytum officinale (comfrey) but only
when it is mature
3. Perfoliate: where the stem appears to grow through the
leaf lamina. e.g. Eucalyptus spp. (gum trees)
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Sheathing
Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Ruwbeemdgras_Poa_trivialis_ligula.jpg
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Decurrent
Verbascum thapsus
Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Starr_040723-0032_Verbascum_thapsus.jpg
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Leaf Arrangement
o Leaf arrangement refers to how leaves are
placed on the stem in relation to each
other.
o The most common leaf arrangements
are:
1. Alternate: leaves are arranged singly on
the stem, there is only one leaf growing at
each node. They may be arranged
around the stem in a spiral or parallel with
Image credit: Wikipedia, viewed 14
each other (alternate distichous)
January 2014
http://commons.wikimedia.org/wiki/File
:Ulistnienie.png
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Leaf Arrangement
2. Opposite: two leaves at
each node growing
opposite to each other.
The leaves are in pairs up
the stem (c).
If each pair is at right-angles
to adjacent pairs then the
arrangement is called
decussate (b).
Image credit: Wikipedia, viewed 14 January 2014
http://commons.wikimedia.org/wiki/File:Ulistnienie.png
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Leaf Arrangement
3. Whorled: when there are more than 2 leaves growing
from the same point of the stem e.g. Aloysia citrodora
(lemon verbena)
Aloysia citrodora
Image credit: bgblogging viewed 14 January 2014
http://www.flickr.com/Images/bg/4693968818/
Image credit: Wikipedia, viewed 14 January 2014
http://commons.wikimedia.org/wiki/File:Ulistnienie.png
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Leaf Arrangement
4. Basal/radical: when the leaves all grow from the base of
the stem (near the radix/root) e.g. Taraxacum officinale
(dandelion)
Image credit: Jan Macario, Wild Plant Database, ND, viewed 14
January 2014 http://wildplantdatabase.net/plantImages/21_B.jpg
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Practical Session
o Draw a specimen with simple leaves. Label the petiole,
lamina, leaf axil. What is the arrangement of leaves?
o Draw a specimen with compound leaves. Label the
petiole, lamina, leaf axil. What is the arrangement of
leaves?
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Leaf Shape
o The leaf shape refers to the shapes of the lamina of a leaf
or leaflets.
o The leaf shape is characteristic for a species, however
there can be some variation within a species or on an
individual plant.
o Leaf shape is not always definitive for plant families so it is
worth noting that when trying to describe a leaf’s shape it
is best to first identify which part of the leaf is widest –
apex (tip), middle or base.
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Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Leaf_morphology.svg
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Could you Name these shapes?
http://commons.wikimedia.org/wiki/File:Kszta%C5%82ty_li%C5%9B
ci_2b.svg Viewed 26/6/14
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Leaf Venation
o The veins of a leaf contain xylem and
phloem which run along the stem and
petiole and into the leaf lamina. The
pattern made by veins is called the leaf
venation.
xylem
phloem
o The most common venation is reticulate
where the veins branch out from the main
vein in the midrib into finer and finer
traces.
o Reticulate venation is found in
dicotyledons.
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Leaf Venation
o Monocotyledons usually have parallel venation where
there is no main vein and several veins of more or less
equal size run parallel to each other along the length of
the leaf.
o In some monocot plants the leaf venation is said to be
penniveined.
o This is when smaller veins run parallel to each other away
from the midrib.
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Parallel Venations
Typical lily leaf
https://upload.wikimedia.org/wikipedia/commons/7/70/Alstroemeria_au
rea_%27Peruvian_lily%27_%28Alstroemeriaceae%29_leaves.JPG
viewed 29/6/14
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Leaf Margin
o The leaf margin is the edge of the lamina.
o If the edge of the lamina is an even curve then the margin
is said to be entire.
o If the margin is not entire then the edge of the lamina is
indented in some way.
o There are many terms used to describe the margin
according to whether the indentations are smooth or
sharp, and what size they are in relation to the leaf.
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Leaf Margin
Entire leaf margin
Dentate leaf margin
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Leaf Margin
o There are a few terms to describe the margin that also
describe the shape of the leaves:
1. Runcinate: like a dandelion leaf, with sharp indentations,
widest at the apex and tapering towards the base.
2. Lyrate: like runcinate but with blunt indentations.
3. Palmatifid: where the lamina is deeply dissected into
finger-like projections e.g. maple leaf.
o These are, however not the most typical of examples for Australia. Refer to
Capon 3rd Ed., p.37 for diagrams of these type of margins.
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Leaf Margin
Schefflera actinophylla (Umbrella tree) – an example of a
compound palmatifid margin
Image credit: Schefflera Arboricola Hay, 2009, viewed 14 January
2014 http://www.fotopedia.com/items/flickr-3485519595
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Leaf Surface
o Plants need to absorb and release carbon dioxide and oxygen,
but they also need to conserve water.
o They can’t afford to lose more water than they absorb or they
would dehydrate.
o The surface of leaves are coated in cuticle to prevent excessive
water loss.
o There are special openings called stomata that can open and
close to allow gaseous exchange without letting too much water
evaporate.
o As well as cuticle many leaves have hairs or oil glands.
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Leaf Surface
o Oil glands can be seen when the leaf is held up to the
light. e.g. Hypericum perforatum (St John’s Wort) and
Eucalyptus spp.
o Some leaves have “warty” or mealy surfaces.
Hypericum perforatum
Image credit: Wikipedia, viewed 14 January 2014
http://commons.wikimedia.org/wiki/File:Hypericum_perf
© Endeavour College ratum_(5259020624).jpg
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Vestiture
There are a number of terms used to describe the
vestiture (covering) and surface of leaves. Examples
include:
1. Glabrous: a smooth surface without hairs or other
covering
2. Glaucous: a bluish waxy surface (common in
eucalypts)
3. Pubescent: a covering of fine hairs
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Glabrous: a smooth surface leaf
http://commons.wikimedia.org/wiki/File:Persoonia_levis_leaf_1.jp
g viewed 26/6/14
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Glaucous: a bluish waxy surface
http://commons.wikimedia.org/wiki/File:Eucalyptus_rhodantha_var._rhoda
ntha_leaves_closeup.jpg viewed 26/6/14
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Pubescent: a covering of fine hairs
http://commons.wikimedia.org/wiki/File:Campanula_rapun
culoides_%284996751323%29.jpg viewed 26/6/14
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Stipules
o Stipules are small leaf-like
structures found in pairs on the
base of the petiole (e.g Rosa
canina opposite)
o Not all plants have stipules, and
they vary in appearance.
o Stipules are characteristic of
some plant families e.g.
Rosaceae.
Rosa canina
Image credit: Wikipedia, viewed 14 January 2014,
http://en.wikipedia.org/wiki/File:Rosa_canina_blatt_20
05.05.26_11.50.13.jpg
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Ochrea
o An ochrea is a
membranous sheath
found around the nodes
of certain plants.
o The ochrea is formed
from fused stipules and
is characteristic of the
Polygonaceae family.
Ocreae of a Persicaria maculosa
Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Ocreae_of_a_Persicaria_maculosa
_2006-aug-10_Gothenburg_Sweden.jpg
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Function of leaves
Three functions of leaves which we will discuss:
1. Photosynthesis
2. Maintenance of water balance
3. Gaseous exchange
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Photosynthesis
o The major function of leaves is Photosynthesis.
o “Phot” means light; “synthesis” means to put together.
o Photosynthesis is the process by which plants use the
sun’s energy to join carbon, hydrogen and oxygen into
sugar molecules.
o The energy stored in these molecules is then available for
the plant and ultimately other organisms to use.
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Plagiomnium affine cells with visible chloroplasts
Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Plagiomnium_affine_laminazelle
n.jpeg
Photosynthesis
Image credit: Wikipedia, viewed 14 January 2014
http://en.wikipedia.org/wiki/File:Photosynthesis.gif
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Photosynthesis
o Plants contain chlorophyll, which makes them green.
o The pigments in chlorophyll absorb light energy and
electrons are boosted to a higher energy state.
o As the electrons drop to lower state again the energy they
had is transferred to certain carrier molecules (ADP-ATP).
o The energy of these molecules is later used to join
carbon, hydrogen and oxygen atoms together to form
glucose.
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Photosynthesis
o The equation for photosynthesis is as
below:
6CO2 + 6H2O (+ light energy) =
C6H12O6 + 6O2
o The glucose molecules are joined
together into starch which is transported
around the plant by phloem.
o Oxygen is released to the atmosphere.
o This is the basis of all food
Image credit: Wikipedia, viewed 14 January 2014
http://upload.wikimedia.org/wikipedia/commons/0/0
c/Simple_Imagesynthesis_overview.svg
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Photosynthesis
o Living things can be divided into two types.
o Autotrophs that are able to make their own food, and
heterotrophs which are not.
o Heterotrophs therefore have to eat their food.
o Most plants are autotrophs, humans and animals are
heterotrophs.
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Photosynthesis
o When the plant needs energy the starch is split into
glucose molecules again.
o The glucose is broken down into carbon dioxide and in the
process electrons are released.
o These electrons pass their energy to carrier molecules.
o The energy is now available to do work within the plant
body.
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Photosynthesis
o This process is called respiration and is similar to what
happens in human cells with the glucose from the food we
eat.
o Oxygen is needed for respiration, so photosynthesis is
significant to us for two reasons:
1. It provides the original carbohydrates in the food chain
2. It produces oxygen
o Without oxygen most heterotrophs would not be able to use
the energy that is stored in glucose.
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Maintenance of water balance
o Leaves maintain water
balance in the plant by
controlling evaporation and
producing movement of
fluid in the xylem.
o The surface cells of leaves
have a waxy outer layer
(cuticle) to prevent
excessive water loss.
Eucalyptus spp. all have a
waxy coating on their
leaves
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Gaseous Exchange
o Plants need to absorb and release gases, specially
carbon dioxide and oxygen which are necessary for
photosynthesis and respiration.
o The leaf surface has special pores called stomata, that
allow gases to pass in and out of the leaf.
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Leaf Function
o Each stomata has two
guard cells which can
open and close the pore
as necessary
o Thus the need to
preserve water is
balanced with the need to
exchange gases
Tomato leaf stomate
Image credit: Wikipedia, updated 14 January 2014
http://en.wikipedia.org/wiki/File:Tomato_leaf_stomate_1-color.jpg
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Leaf Modifications
o As with roots and stems, leaves also have
modifications.
o The leaves of some plants have evolved to perform
special functions:
o
o
o
o
o
Tendrils
Spines or thorns
Water storage
Traps
Bracts
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Tendrils
These are modified
leaves that wrap around
structures they
encounter to support
climbing plants.
Image credit: Wikipedia, updated 14 January 2014
http://en.wikipedia.org/wiki/File:Kurgiv%C3%A4%C3%A4t.jpg
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Spines
Modified leaves that provide protection for the plant
Image credit: Wikipedia, updated 14 January 2014
http://en.wikipedia.org/wiki/File:Cactus1web.jpg
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Water Storage
Succulent plant leaves have become adapted for water storage.
Aloe spp.
Photograph with permission – Wendy Williams
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Traps
In carnivorous plants the leaves
have evolved to form structures
that trap small animals. (Tan 2013, p.41)
Why do you think these plants
need insects?
Dionaea muscipula
(Venus Flytrap)
Photograph with permission – Wendy Williams
Image credit: Wikipedia, updated 14 January 2014
http://en.wikipedia.org/wiki/File:VFT_ne1.JPG
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Video
o Watch a video on carnivorous plants:
o https://www.youtube.com/watch?v=ktIGVtKdgwo
From David Attenborough’s DVD - ‘Secret Life of Plants’
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Bracts
o Bracts grow in a range of
shapes and sizes.
o They often look like leaves
but are usually smaller.
o Bracts are most easily
recognised by the position
in which they grow rather
than their appearance.
Bougainvillea (above) & Pontsettia (below)
Photograph with permission – Wendy Williams
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Involucral Bracts
o They grow at the base of
flower stalks or under the
flower itself.
o In the Asteraceae family, rows
of long thin bracts called
involucral bracts surround the
flower head.
o In the Poaceae family each
flower is enclosed in a pair of
bracts.
Silybum marianum
(St Mary's Thistle)
Image credit: Wikipedia, updated 14 January 2014
http://en.wikipedia.org/wiki/File:Milk_thistle_flowerhead.jpg
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Spaths
o These bracts form a large sheath that protects the spadix,
the central column, which is really a collection of tiny
flowers (inflorescence). (Capon, B 2012, p. 209)
o Spathiphyllum wallisii
Photographs with permission – Wendy Williams
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Tutorial Session
o Practical: Check on your monocotyledon and
dicotyledon seeds germinating in the cottonwool and
notice the changes since last week
o Participate in the class exercises regarding leaves and
identification
o Student workbook: Session 9 - work through the
exercises and answer the questions.
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Next Week
o Preparation:
o Please read the chapter in your textbook on flowers
and inflorescence.
o If you have access to some flowers, bring them into
class as we will be dissecting flowers to understand
their arrangements.
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Suggested Readings
o Capon, B. (2010). Botany for gardeners. Portland, OR.: Timber Press.
Pp.50-55.
o Clarke, I. & Lee, H. (1987). Name that flower: The identification of
flowering plants. Carlton, Vic: Melbourne University Press.
Pp. 42-48 on leaves.
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References
Texts:
o Capon, B. (2010). Botany for gardeners. Portland, OR.: Timber Press
o Clarke, I. & Lee, H. (1987). Name that flower: The identification of
flowering plants. Carlton, Vic: Melbourne University Press.
o Tan, E 2004, Herbal Preparations Laboratory Manual, Northern
Melbourne Institute of TAFE, Victoria, Australia.
o Tan, E. (2013). Botany of the flowering plants (4th ed.). Preston, Vic:
Northern Melbourne Institute of TAFE.
o Wohlmuth, H. (1992). An Introduction to Botany and Plant
Identification. (2nd ed.). Lismore, NSW: MacPlatypus Productions
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