session nine plant morphology: leaves · © endeavour college of natural health endeavour.edu.au 1...
TRANSCRIPT
© Endeavour College of Natural Health endeavour.edu.au 1
WHMF121
Session Nine
Plant
Morphology:
Leaves
(Photograph with permission David Stelfox)
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Topic Overview
o Leaf anatomy (lamina, petiole, axis, mid-
rib etc)
o Leaf characteristics (structure,
attachment, arrangement, shape,
venation and margin).
o The functions of leaves
o Leaf modifications (tendrils, spines,
bracts)
o Photosynthesis
The characteristic leaf of Ginkgo
biloba. Notice the species name
identifies the bilobate leaf
shape.
(http://commons.wikimedia.org/wiki/File:Gin
kgo_biloba_scanned_leaf.jpg)
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Leaves• Leaves consist of a leaf blade or lamina, which is often,
but not always, carried on a stem called the petiole.
• The petiole may extend along the centre of the leaf
forming the mid-rib.
• Leaves grow at the nodes of a stem.
• The angle formed by the leaf and the
stem is the leaf axil.
• Axillary buds are found in leaf axils
(http://commons.wikimedia.org/wiki/File:Maple_Leaves.jpg)
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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.
(Science and Plants for School, n.d.,
http://www.flickr.com/Images/71183136@N08/7128074957/in/Imagestream/)
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Leaf Characteristics
• Structure: Leaves are said to
be either simple or compound
in structure. This refers to the
lamina of the leaf
• Attachment: Refers to how
the leaf joins the stem
• Arrangement: Leaves grow
on stems in distinctive
patterns
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Leaf Characteristics
• Shape: Refers to the shape
of the lamina of leaf or
leaflets
• Venation: The pattern of the
veins on a leaf
• Margin: The leaf margin is
the edge of the lamina
(http://en.wikipedia.org/wiki/File:Silver_maple_leaf.jpg;
(http://en.wikipedia.org/wiki/File:Fern_detail.jpg)
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Leaf Structure
Leaves are described as simple or compound,
depending on the lamina
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Leaf Structure
Simple leaves have one continuous lamina.
o Leaves of Taraxacum officinale (Dandelion) see picture opposite, Mentha x piperita(Peppermint) and Galium aparine (Clivers) are simple leaves.
(http://commons.wikimedia.org/wiki/File:Dandelion-leaf.jpg)
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Leaf Structure
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)
(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.
o These are called bipinnate
leaves
Simple Pinnate Leaf
(http://en.wikipedia.org/wiki/File:Fern_frond_pinnate.jpg)
Binnate Leaf
(Gerus, n.d., 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) 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 Attachment
How the leaf joins the stem: This may be;
• Articulate: when a definite joint can be seen where
the leaf or petiole are attached to the stem. e.g.
Mentha x piperita (peppermint), Sambucus nigra
(elderflower)
• Petiolate: if a petiole connects the leaf to the stem
e.g. M. piperita, Sambucus nigra
• 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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Special Leaf Attachments
These special attachments include:
• Sheathing: where the bases of the petioles wrap
around the stem e.g. Petroselinum crispum
(parsley), many grasses.
• Decurrent: where the lamina extends onto the side
of the stem e.g. Symphytum officinale (comfrey) but
only when it is mature
• Perfoliate: where the stem appears to grow
through the leaf lamina. e.g. Eucalyptus spp. (gum
trees)
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Sheathing
(http://en.wikipedia.org/wiki/File:Ruwbeemdgras_Po
a_trivialis_ligula.jpg)
Sheathing: where the
bases of the petioles
wrap around the stem
e.g. Petroselinum
crispum (parsley), many
grasses.
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Decurrent
Verbascum thaspus
(http://en.wikipedia.org/wiki/File:Starr_040723-0032_Verbascum_thapsus.jpg)
Decurrent: where the
lamina extends onto the
side of the stem e.g.
Symphytum officinale
(comfrey) but only when
it is mature
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Leaf Arrangement
How leaves are placed on the stem in relation
to each other.
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 each
other (alternate distichous) (http://commons.wikimedia.or
g/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).
(http://commons.wikimedia.o
rg/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)
(http://commons.wikimedia.org/wi
ki/File:Ulistnienie.png)
Aloysia citrodora
(http://www.flickr.com/I
mages/bg/4693968818
/)
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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)
(Macario, Wild Plant Database, n.d.,
http://wildplantdatabase.net/plantImages/21_B.jpg)
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Leaf Shape
o 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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(http://en.wikipedia.org/wiki/File:Leaf_morphology.svg)
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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.
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.
phloem
xylem
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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.
• This is when smaller veins run parallel to each other
away from the midrib.
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Parallel Venations
(https://upload.wikimedia.org/wikipedia/commo
ns/7/70/Alstroemeria_aurea_%27Peruvian_lily
%27_%28Alstroemeriaceae%29_leaves.JPG
Typical lily leaf
Altstroemeria aurea
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Leaf Margin
• The leaf margin is the edge of the lamina.
• If the edge of the lamina is an even curve then the
margin is said to be entire.
• If the margin is not entire then the edge of the lamina is
indented in some way.
• 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
There are a few terms to describe the margin that also describe the shape of the leaves:
Runcinate: like a dandelion leaf, with sharp indentations, widest at the apex and tapering towards the base.
Lyrate: like runcinate but with blunt indentations.
Palmatifid: where the lamina is deeply dissected into finger-like projections e.g. maple leaf.
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 Arboricola Hay,2009,
http://www.fotopedia.com/items/flickr-3485519595)
Compound Palmatifid Margin
Schefflera actinophylla
(Umbrella tree) – an example
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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 Surfaceo 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.
(http://commons.wikimedia.org/wiki/File:Hypericum_
perforatum_(5259020624).jpg)
Hypericum perforatum
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Vestiture
The covering and surface of leaves:
Examples include:
• Glabrous: a smooth surface without hairs or
other covering
• Glaucous: a bluish waxy surface (common in
eucalypts)
• 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.jpg)
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Glaucous: a bluish waxy surface
(http://commons.wikimedia.org/wiki/File:Eucalyptus_rhodantha_var._rhod
antha_leaves_closeup.jpg)
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Pubescent: a covering of fine hairs
(http://commons.wikimedia.org/wiki/File:Campanula_rapu
nculoides_%284996751323%29.jpg)
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Stipules• Stipules are small leaf-like
structures found in pairs on
the base of the petiole (e.g
Rosa canina opposite)
• Not all plants have stipules,
and they vary in
appearance.
• Stipules are characteristic of
some plant families e.g.
Rosaceae. (http://en.wikipedia.org/wiki/File:Rosa_canina_blatt_20
05.05.26_11.50.13.jpg)
Rosa canina
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Ochrea
• An ochrea is a
membranous sheath
found around the nodes
of certain plants.
• The ochrea is formed
from fused stipules and
is characteristic of the
Polygonaceae family.
Ocreae of a Persicaria maculosa
(http://en.wikipedia.org/wiki/File:Ocreae_of_a_Persicaria_ma
culosa_2006-aug-10_Gothenburg_Sweden.jpg)
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Function of leaves
Three functions of leaves:
1. Photosynthesis
2. Maintenance of water balance
3. Gaseous exchange
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Photosynthesis
• The major function of leaves is Photosynthesis.
• “Phot” means light; “synthesis” means to put together.
• Photosynthesis is the process by which plants use the
sun’s energy to join carbon, hydrogen and oxygen into
sugar molecules.
• The energy stored in these molecules is then available for
the plant and ultimately other organisms to use.
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(http://en.wikipedia.org/wiki/File:Photosynthesis.gif
Plagiomnium affine cells with visible chloroplasts
(http://en.wikipedia.org/wiki/File:Plagiomni
um_affine_laminazellen.jpeg)
Photosynthesis
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Photosynthesis
• Plants contain chlorophyll, which makes them green.
• The pigments in chlorophyll absorb light energy and
electrons are boosted to a higher energy state.
• As the electrons drop to lower state again the energy they
had is transferred to certain carrier molecules (ADP-ATP).
• The energy of these molecules is later used to join carbon,
hydrogen and oxygen atoms together to form glucose.
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Photosynthesis
• The equation for photosynthesis is
as below:
• 6CO2 + 6H2O (+ light energy) =
C6H12O6 + 6O2
• The glucose molecules are joined
together into starch which is
transported around the plant by
phloem.
• Oxygen is released to the
atmosphere.
• This is the basis of all food (http://upload.wikimedia.org/wikipedia/com
mons/0/0c/Simple_Imagesynthesis_overvi
ew.svg)
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Photosynthesis
• Living things can be divided into two types.
• Autotrophs that are able to make their own food, and
heterotrophs which are not.
• Heterotrophs therefore have to eat their food.
• Most plants are autotrophs, humans and animals are
heterotrophs.
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Photosynthesis
• When the plant needs energy the starch is split into
glucose molecules again.
• The glucose is broken down into carbon dioxide and in
the process electrons are released.
• These electrons pass their energy to carrier molecules.
• The energy is now available to do work within the plant
body.
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Photosynthesis
• This process is called respiration and is similar to what
happens in human cells with the glucose from the food
we eat.
• Oxygen is needed for respiration, so photosynthesis is
significant to us for two reasons:
• It provides the original carbohydrates in the food chain
• It produces oxygen
• 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
• Each stomata has two
guard cells which can
open and close the pore
as necessary
• Thus the need to preserve
water is balanced with the
need to exchange gases
Tomato leaf stomata
(http://en.wikipedia.org/wiki/File:Tomato_leaf_stomate_1-color.jpg)
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Leaf Modifications
As with roots and stems, leaves also have modifications.
The leaves of some plants have evolved to perform
special functions:
o Tendrils
o Spines or thorns
o Water storage
o Traps
o Bracts
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Tendrils
These are modified
leaves that wrap around
structures they
encounter to support
climbing plants.
(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
(http://en.wikipedia.org/wiki/File:Cactus1web.jpg)
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Water Storage
Succulent plant leaves have become adapted for water
storage.
(Photograph with permission – Wendy Williams)
Aloe spp.
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TrapsIn 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)
(http://en.wikipedia.org/wiki/File:VFT_ne1.JPG)(Photograph with permission – Wendy Williams)
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Bracts• Bracts grow in a range
of shapes and sizes.
• They often look like
leaves but are usually
smaller.
• Bracts are most easily
recognised by the
position in which they
grow rather than their
appearance.
(Photograph with permission – Wendy Williams)
Bougainvillea (above) & Pontsettia (below)
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Involucral Bracts• They grow at the base of
flower stalks or under the
flower itself.
• In the Asteraceae family, rows
of long thin bracts called
involucral bracts surround the
flower head.
• In the Poaceae family each
flower is enclosed in a pair of
bracts. Silybum marianum
(St Mary's Thistle)(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, 2012, p. 209)
o Spathiphyllum wallisii
(Photographs with permission – Wendy Williams)
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Leaves used in Herbal Medicine
Medicinal plants mentioned in this lecture, where the leaf or its modifications
are used for therapeutic purposes, either as a food or medicinally are:
Ginkgo biloba – ginkgo
Taraxacum officinale - dandelion
Mentha x piperita - peppermint
Galium aparine – clivers
Sambucus nigra – elder
Aesculus hippocastanum – horsechestnut
Petroselinum crispum - parsley
Verbascum thaspus – Mullein
Aloysia citrodora – Lemon Verbena
In Latin nomenclature, when the leaf of a plant is used it is identified as an
aerial part or as ‘folia’
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Botany Tutorial
Leaves used in Herbal MedicineIdentify environmental conditions required for the growth of these plants.
What sort of plants are these listed medicinal herbs?
What season are the leaves harvested?
Are there any requirements for preserving the herb?
Ginkgo biloba – ginkgo
Taraxacum officinale - dandelion
Mentha x piperita - peppermint
Galium aparine – clivers
Sambucus nigra – elder
Aesculus hippocastanum – horsechestnut
Petroselinum crispum - parsley
Verbascum thaspus – Mullein
Aloysia citrodora – Lemon Verbena
What are some other leaves that are used in herbal medicine?
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Video
o Watch a video on carnivorous plants:
o Carnivorous Plants_Attenborough
From David Attenborough’s DVD - ‘Secret Life of Plants’
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Video
o Stomata - The Perfect Pump
o Perfect Pump_Stomata_Attenborough
From David Attenborough’s DVD - ‘The Private Life of Plants’.
BBC
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Botany 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
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Botany Tutorial
Leaf Structure
How do you know if a leaf is simple or compound?
o Look at the leaf axil and axillary bud – macro,
micro and with magnifying glass.
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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Botany Tutorial
Name these shapes?
(http://commons.wikimedia.org/wiki/
File:Kszta%C5%82ty_li%C5%9Bci
_2b.svg)
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Botany Tutorial - Photosynthesis
• In small groups, identify each of the stages of
photosynthesis
• How would you describe this to a child?
• What is the correct scientific terminology for this
process?
• What increases/decreases the rate of photosynthesis?
• Where can you find more information about this?
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Botany Tutorial 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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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
Capon, B. (2010). Botany for gardeners (pp. 50-55). Portland, OR:
Timber Press.
Clarke, I., & Lee, H. (1987). Name that flower: The identification of
flowering plants (pp. 42-48). Carlton, Vic: Melbourne University
Press.
Epel, T.J. (2008). Botany in a day: The patterns method of plant
identification (5th ed.). Montana, USA: HOPS Press.
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References
Capon, B. (2010). Botany for gardeners. Portland, OR: Timber Press.
Clarke, I., & Lee, H. (1987). Name that flower: The identification of
flowering plants. Carlton, Vic: Melbourne University Press.
Mauseth, J. (2018). Botany: An introduction to plant biology (6th ed.).
MA, USA: Jones & Bartlett Learning.
Tan, E. (2004). Herbal preparations laboratory manual. Victoria,
Australia: Northern Melbourne Institute of TAFE.
Tan, E. (2013). Botany of the flowering plants (4th ed.). Preston, Vic:
Northern Melbourne Institute of TAFE.
Wohlmuth, H. (1992). An introduction to botany and plant
identification (2nd ed.). Lismore, NSW: MacPlatypus Productions.
© Endeavour College of Natural Health endeavour.edu.au 68
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