Botany Basics 3Botany Basics 3

Crop Science 1Crop Science 1

Fall 2004Fall 2004

September 28, 2004September 28, 2004

Leaf FunctionLeaf Function

Principal functionPrincipal function Photosynthesis Photosynthesis

to absorb sunlight to manufacture plant to absorb sunlight to manufacture plant sugarssugars

Surfaces flattened to present a large area Surfaces flattened to present a large area for efficient light absorptionfor efficient light absorption

Leaf StructureLeaf Structure

BladeBlade expanded thin structure expanded thin structure

on either side of the on either side of the midrib and usually the midrib and usually the largest, most largest, most conspicuous part of a conspicuous part of a leafleaf

Leaf StructureLeaf Structure

PetiolePetiole Stem-like appendage Stem-like appendage

which holds the leaf which holds the leaf away from the stem away from the stem

The base is attached The base is attached to the stem at a nodeto the stem at a node

Vary in length or may Vary in length or may be lacking entirely, in be lacking entirely, in which case the leaf which case the leaf blade is described as blade is described as sessile or stalklesssessile or stalkless

Leaf StructureLeaf Structure

Leaf axilLeaf axil The node where a petiole The node where a petiole

meets a stemmeets a stem Contain axillary budsContain axillary buds

single buds or bud clusterssingle buds or bud clusters Either active or dormantEither active or dormant Will develop into stems or Will develop into stems or

leaves under the right leaves under the right conditionsconditions

Leaf Blade StructureLeaf Blade Structure

A leaf A leaf blade is blade is composed composed of several of several layers layers

EpidermisEpidermis

Layer of thick, tough cells on the top and Layer of thick, tough cells on the top and bottom bottom

Primary function is to protect the other Primary function is to protect the other layers of leaf tissuelayers of leaf tissue

The arrangement of epidermal cells The arrangement of epidermal cells determines the leaf's surface texturedetermines the leaf's surface texture

Some leaves have hairs (pubescence), Some leaves have hairs (pubescence), which are extensions of epidermal cellswhich are extensions of epidermal cells

CuticleCuticle

Part of the epidermisPart of the epidermis Produces a waxy layer called cutinProduces a waxy layer called cutin

Protects the leaf from dehydration and disease Protects the leaf from dehydration and disease The amount of cutin on a leaf increases with The amount of cutin on a leaf increases with

increasing light intensityincreasing light intensity Move plants from shade into full sunlight gradually to allow Move plants from shade into full sunlight gradually to allow

the cutin layer to build up and protect the leaves from rapid the cutin layer to build up and protect the leaves from rapid water loss or sunscaldwater loss or sunscald

Repels waterRepels water Many pesticides contain a spray additive to help the Many pesticides contain a spray additive to help the

product adhere to, or penetrate, the cutin layer (surfactant)product adhere to, or penetrate, the cutin layer (surfactant)

Guard CellsGuard Cells

Special epidermal cells Special epidermal cells Open and close in response to environmental Open and close in response to environmental

stimuli (changes in weather and light)stimuli (changes in weather and light) Conditions that cause a loss of water (high Conditions that cause a loss of water (high

temperature, low humidity), or the absence of light temperature, low humidity), or the absence of light stimulate guard cells to closestimulate guard cells to close

Regulate the passage of water, oxygen, and Regulate the passage of water, oxygen, and carbon dioxide into and out of the leaf through tiny carbon dioxide into and out of the leaf through tiny openings called stomataopenings called stomata

In most species, the majority of the stomata are In most species, the majority of the stomata are located on the underside of leaveslocated on the underside of leaves

MesophyllMesophyll

Located between the upper and lower Located between the upper and lower epidermisepidermis

Divided into:Divided into: dense upper layer (palisade mesophyll) dense upper layer (palisade mesophyll) lower layer that contains lots of air space lower layer that contains lots of air space

(spongy mesophyll) (spongy mesophyll) Located within the mesophyll cells are Located within the mesophyll cells are

chloroplastschloroplasts Where photosynthesis takes placeWhere photosynthesis takes place

Types of LeavesTypes of Leaves

There are many kinds of plant leaves: There are many kinds of plant leaves: FoliageFoliage Scale leavesScale leaves Seed leavesSeed leaves Spines and tendrilsSpines and tendrils Storage leavesStorage leaves BractsBracts

Modified Leaves

FoliageFoliage

Most common and conspicuous leaves Most common and conspicuous leaves Primary location of photosynthesisPrimary location of photosynthesis

Scale leavesScale leaves

CataphyllsCataphylls Found on rhizomes and budsFound on rhizomes and buds Enclose and protect rhizomes and budsEnclose and protect rhizomes and buds

Seed leavesSeed leaves

CotyledonsCotyledons Found on embryonic plantsFound on embryonic plants Store food for the developing seedlingStore food for the developing seedling

Spines and TendrilsSpines and Tendrils

Found on plants such as barberry and Found on plants such as barberry and pea plantspea plants

Protect a plantProtect a plant Help support stemsHelp support stems

Storage LeavesStorage Leaves

Found on bulbous plants and succulents Found on bulbous plants and succulents Store foodStore food

BractsBracts

Often are brightly colored Often are brightly colored The showy structures on dogwoods and The showy structures on dogwoods and

poinsettias are bracts, not petalspoinsettias are bracts, not petals

VenationVenation

The vascular bundles of xylem and The vascular bundles of xylem and phloem extend from the stem, through phloem extend from the stem, through the petiole, and into the leaf blade as the petiole, and into the leaf blade as veins. veins.

The term venation refers to how veins The term venation refers to how veins are distributed in the blade. are distributed in the blade.

There are two principal types of venation: There are two principal types of venation: parallel-veined and net-veined parallel-veined and net-veined

VenationVenation

Parallel-Veined LeavesParallel-Veined Leaves

Numerous veins run essentially parallel to each Numerous veins run essentially parallel to each other and are connected laterally by minute, other and are connected laterally by minute, straight veinlets straight veinlets

Occur most often on monocotyledonous plants Occur most often on monocotyledonous plants The most common type of parallel veining is The most common type of parallel veining is

found in plants of the grass family, whose veins found in plants of the grass family, whose veins run from the leaf's base to its apexrun from the leaf's base to its apex

Another type of parallel venation is found in Another type of parallel venation is found in plants such as banana whose veins run plants such as banana whose veins run laterally from the midriblaterally from the midrib

Net-Veined LeavesNet-Veined Leaves

Also called reticulate-veinedAlso called reticulate-veined Veins branch from the main rib or ribs Veins branch from the main rib or ribs

and subdivide into finer veinlets then and subdivide into finer veinlets then unite in a complicated networkunite in a complicated network

More resistant to tearing More resistant to tearing Occur on dicotyledonous plantsOccur on dicotyledonous plants

Pinnate vs. PalmatePinnate vs. Palmate

Either Either PinnatePinnate

The veins extend laterally from the midrib to The veins extend laterally from the midrib to the edge the edge

Apples, cherries, and peachesApples, cherries, and peaches PalmatePalmate

The principal veins extend outward, like the The principal veins extend outward, like the ribs of a fan, from the base of the leaf blade ribs of a fan, from the base of the leaf blade

Grapes and maplesGrapes and maples

Common Blade ShapesCommon Blade Shapes

LanceolateLanceolate Longer than wide and Longer than wide and

tapering toward the tapering toward the apex and baseapex and base

LinearLinear Narrow, several times Narrow, several times

longer than wide, and longer than wide, and of approximately the of approximately the same width same width throughoutthroughout

Common Blade ShapesCommon Blade Shapes

Cordate Cordate Heart-shapedHeart-shaped Broadly ovate, Broadly ovate,

tapering to an acute tapering to an acute apex, with the base apex, with the base turning in and forming turning in and forming a notch where the a notch where the petiole is attachedpetiole is attached

Common Blade ShapesCommon Blade Shapes

EllipticalElliptical About two or three About two or three

times as long as wide, times as long as wide, tapering to an acute tapering to an acute or rounded apex and or rounded apex and basebase

OvateOvate Egg-shaped, basal Egg-shaped, basal

portion wide, tapering portion wide, tapering toward the apextoward the apex

Common Margin FormsCommon Margin Forms

EntireEntire Smooth edge with no Smooth edge with no

teeth or notchesteeth or notches

CrenateCrenate Rounded teethRounded teeth

DentateDentate Teeth ending in an Teeth ending in an

acute angle pointing acute angle pointing outwardoutward

Common Margin FormsCommon Margin Forms

SerrateSerrate Small, sharp teeth Small, sharp teeth

pointing toward the pointing toward the apexapex

IncisedIncised Sharp, deep, irregular Sharp, deep, irregular

teeth or incisionsteeth or incisions Lobed Lobed

Incisions that extend Incisions that extend less than halfway to less than halfway to the midribthe midrib

Common Apex ShapesCommon Apex Shapes

AcuteAcute Ending in an acute Ending in an acute

angle, with a sharp, angle, with a sharp, but not acuminate, but not acuminate, pointpoint

AcuminateAcuminate Tapering to a long, Tapering to a long,

narrow pointnarrow point ObtuseObtuse

Tapering to a rounded Tapering to a rounded edgeedge

Common Base ShapesCommon Base Shapes

CuneateCuneate Wedge-shaped; Wedge-shaped;

triangular with the triangular with the narrow end at the narrow end at the point of attachmentpoint of attachment

ObtuseObtuse Tapering to a rounded Tapering to a rounded

edgeedge CordateCordate

Turning in and Turning in and forming a notchforming a notch

Plant IdentificationPlant Identification

Leaves are useful for plant identification: Leaves are useful for plant identification: Leaf's venationLeaf's venation Blade and margin shapesBlade and margin shapes Apex and base shape Apex and base shape Leaf type Leaf type Leaf arrangementLeaf arrangement

Leaf TypeLeaf Type

Simple leavesSimple leaves Leaf blade is a single, Leaf blade is a single,

continuous unitcontinuous unit Compound leavesCompound leaves

Composed of several Composed of several separate leaflets arising from separate leaflets arising from the same petiolethe same petiole

Some leaves are doubly Some leaves are doubly compoundcompound

Leaf type can be confusing, Leaf type can be confusing, because a deeply lobed because a deeply lobed simple leaf may look like a simple leaf may look like a compound leafcompound leaf

Leaf ArrangementLeaf Arrangement

OppositeOpposite Positioned across the Positioned across the

stem from each other, stem from each other, with two leaves at with two leaves at each nodeeach node

Alternate (spiral) Alternate (spiral) Leaves are arranged Leaves are arranged

in alternate steps in alternate steps along the stem, with along the stem, with only one leaf at each only one leaf at each nodenode

Leaf ArrangementLeaf Arrangement

WhorledWhorled Arranged in circles Arranged in circles

along the stemalong the stem

RosulateRosulate Arranged in a rosette Arranged in a rosette

around a stem with around a stem with extremely short nodesextremely short nodes

Leaves as FoodLeaves as Food

Leaf bladeLeaf blade Chives, collards, dandelions, endives, kale, Chives, collards, dandelions, endives, kale,

leaf lettuce, mustard, parsley, spinach and leaf lettuce, mustard, parsley, spinach and Swiss chardSwiss chard

Cluster of fleshy leaf basesCluster of fleshy leaf bases Leeks, onions, and Florence fennelLeeks, onions, and Florence fennel

Petiole Petiole Celery and rhubarbCelery and rhubarb