Session Nine Plant Morphology: Leaves · © Endeavour College of Natural Health endeavour.edu.au 1 WHMF121 Session Nine Plant Morphology: Leaves (Photograph with permission David

© Endeavour College of Natural Health endeavour.edu.au 1

WHMF121

Session Nine

Plant

Morphology:

Leaves

(Photograph with permission David Stelfox)


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)


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)


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/)


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


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)


Leaf Structure

Leaves are described as simple or compound,

depending on the lamina


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)


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


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/)


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.


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).


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)


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.


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


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)


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)


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

/)


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)


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.


(http://en.wikipedia.org/wiki/File:Leaf_morphology.svg)


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


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.


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


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.


Leaf Margin

Entire leaf margin Dentate leaf margin


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.


Leaf Margin

(Schefflera Arboricola Hay,2009,

http://www.fotopedia.com/items/flickr-3485519595)

Compound Palmatifid Margin

Schefflera actinophylla

(Umbrella tree) – an example


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.


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


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


Glabrous: a smooth surface leaf

(http://commons.wikimedia.org/wiki/File:Persoonia_levis_leaf_1.jpg)


Glaucous: a bluish waxy surface

(http://commons.wikimedia.org/wiki/File:Eucalyptus_rhodantha_var._rhod

antha_leaves_closeup.jpg)


Pubescent: a covering of fine hairs

(http://commons.wikimedia.org/wiki/File:Campanula_rapu

nculoides_%284996751323%29.jpg)


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


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)


Function of leaves

Three functions of leaves:

1. Photosynthesis

2. Maintenance of water balance

3. Gaseous exchange


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.


(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


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.


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)


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.


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.


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.


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


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.


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)


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


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)


Spines

Modified leaves that provide protection for the plant

(http://en.wikipedia.org/wiki/File:Cactus1web.jpg)


Water Storage

Succulent plant leaves have become adapted for water

storage.

(Photograph with permission – Wendy Williams)

Aloe spp.


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)


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)


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)


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)


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’


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?


Video

o Watch a video on carnivorous plants:

o Carnivorous Plants_Attenborough

From David Attenborough’s DVD - ‘Secret Life of Plants’

https://www.youtube.com/watch?v=ktIGVtKdgwo


Video

o Stomata - The Perfect Pump

o Perfect Pump_Stomata_Attenborough

From David Attenborough’s DVD - ‘The Private Life of Plants’.

BBC

https://www.youtube.com/watch?v=Qwb6mVeMpW8


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


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.


Botany Tutorial

Name these shapes?

(http://commons.wikimedia.org/wiki/

File:Kszta%C5%82ty_li%C5%9Bci

_2b.svg)


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?


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?


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.


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.


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.


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Documents

Session Nine Plant Morphology: Leaves · © Endeavour College of Natural Health endeavour.edu.au 1 WHMF121 Session Nine Plant Morphology: Leaves (Photograph with permission David