PLANT LEAF

o o o o o o o o o o thin, flat, expanded structures (maximum exposure to light, maximum surface area for absorption) arise from nodes Foliage Leaf - flat green structures involved in photosynthesis must die to be functional typically short-lived, but some are perennial photosynthesis maximal absorption of sunlight absorption of CO2 and liberation of O2 must not lose excessive amounts of water must not allow entry of fungi/bacteria must not be too delicious to animals (liability)

FUNCTIONS:
o o o Photosynthesis: large stipules Protection: thorns prevent herbivory Support: tendrils vascular elements collect sugars and receive water/minerals fingerprint of leaf Midrib midvein from which lateral veins emerge that branch into narrow minor veins; involved mostly in conduction Minor Veins site of material exchange Netted/Reticulate Venation lateral subveins branch from midrib Parallel Venation several major veins of equal prominence arranged parallel to each other; common to monocots

Tripinnate/Thrice Pinnately Compound leaflets are attached to secondary rachis which is attached to tertiary rachis; leaves themselves are bipinnate

F.

VEINS
o o o o o o o

PRIMARY FUNCTIONS: REQUIREMENTS: G.

PALMATELY COMPOUND leaflets are attached to a single

point at petiole tip Unifoliate one leaflet Bifoliate two leaflets Trifoliate three leaflets

EXTERNAL STRUCTURE
A. LAMINA
o o o o o o o leaf blade thin principal expanded structure traps light Dorsal/Abaxial Side upper side of blade, usually smooth and darker in color; exposed to sunlight and wind Ventral/Adaxial Side underside of blade where larger veins protrude; rough and lighter in color dorsiventral bifacial: horizontally oriented isolateral unifacial / isobilateral equifacial: vertically oriented leaf stalk cylindrical or flattened Petiolate leaves with petioles Sessile leaves without petioles; small or long and narrow Support: holds lamina out into the light Position: for maximal absorption of light Prevention of Self-shading: lessens chance of leaves shading other leaves Conduction: vascular tissues Cooling: longer, thinner, more flexible petioles allow blade to flutter and bring fresh air into surface Photosynthesis: leaf flutter; greater space between leaves ensure greater supply of CO2 Protection: leaf flutter prevents insects from alighting modified lamina found in sessile monocots clasps stem and supports leaf blade Ligules outgrowths that protect sheath from accumulation of dirt and stagnant water terminal part of petiole or sheath joins lamina to stem Pulvinus swollen leaf base which allows plant to respond to external stimuli, e.g. gravity or light pair of small leaflike outgrowths at base of petiole protects shoot apical meristem when young photosynthetic when large may be lost as leaves mature Stipulate leaves with stipules Extipulate leaves without stipules

OTHER PARTS o LEAF AXIL angle between stem and petiole o AXILLARY BUDS develop in leaf axil o LEAF MARGIN boundary area extending along edge of leaf o ABSCISSION ZONE at the leaf base perpendicular to
petiole; involved in cutting off leaf when useful life is over o

C. D.

PELTATE
o o o o has petioles attached to center of lamina flat, circular; shield-shaped sessile surrounds or appears to be pierced by stem

PERFOLIATE

LEAF SCAR
cells

protective scar tissue formed by corky swollen

MODIFICATIONS
A. SUPPORT
o o o o

TENDRILS for climbing species (e.g. sweet pea, cucmber,

squash)

FLOATS provides buoyancy for hydrophytes (e.g. water

hyacinth) HOOKS latches onto other structures (e.g. Bigoniaceae) BASE FORMING - false trunk (e.g. banana tree)

B.

PETIOLE
o o o o o o o o o o o

B.

PROTECTION
o o

FUNCTIONS:

BUD SCALES protect developing buds (e.g. oak tree) MOTILE LEAVES move to protect lamina when pressure is
applied (e.g. makahiya) SPINES hard and pointed; protection from herbivory (e.g. desert plants) Spiny Leaves numerous spines on lamina (e.g. heart of flame plant) Spine Leaves thin spines on abnormal-looking lamina (e.g. money cactus) Stipular Spines spines at stipules (e.g. acacia) Apical and Marginal Spines at leaf apex or margin (e.g. century plant)

NATURE
A. SIMPLE
o o o o flat undivided lamina bigger surface area

PINNATELY LOBED veins originate from midrib at separate

points

PALMATELY LOBED veins originate from one common point

C.

LEAF SHEATH
o o o o

C. B. COMPOUND
o leaf divided into leaflets Leaflets/Pinnae several simple leaves attached to petiolule; lack axillary buds Petiolule stalk of leaflet buds at petiolar base Stipels like stipules, are found at leaf base PINNATELY COMPOUND leaflets are attached to rachis rachis extension of petiole resembling a midrib Unipinnate/Simple Pinnately Compound leaflets are attached to primary rachis Bipinnate/Twice Pinnately Compound leaflets are attached to primary rachis which is attached to secondary rachis

STORAGE
o o o

FLESHY LAMINA/SUCCULENT LEAVES thickened leaf

blades (e.g. aloe vera) POCKET LEAVES has pockets (e.g. oak-leaf fern) BULBS formed by leaves that grow close together (e.g. onion, tulip) uncutinized epidermis allows absorbed materials to be transported

D.

LEAF BASE
o o o o o o

D. E.

ABSORPTION
o

E.

STIPULE
o o o o o o

REPRODUCTION
o o o

LEAF LAMINA buds arise from lamina/base/margin (e.g.

katakataka) PETIOLE buds arise from petiole tip CUTTINGS plantlets come from leaf cuttings

F.

ATTRACTION
o o

3.

VASCULAR BUNDLE / VEINS

o supply water, minerals, and carry dissolved sugars o Leaf Traces 1, 3, 5 vascular bundles which branch from stem vascular bundles and diverge toward petiole o Midrib: circular or crescent-shaped; has vascular cambium

B.

VARIEGATION varied coloration in leaves (e.g. San Francisco

plant)

TYPES 1. KRANZ
o occurs in plants with C4 photosynthesis (carbon dioxide transport o adapts plants to arid environments o wreath-like o 2 types of chloroplasts 2 photosynthetic pathways: Mesophyll Bundle sheath cells (centrifugal manner) o lack palisade parenchyma and spongy mesophyll

BRACTS petalloid leaf structures resembling flowers of varied

coloration (e.g. poinsettia)

G.

NITROGEN PROCUREMENT
o

o Bundle Parenchyma
Separates bundle from mesophyll conducts water and nutrient materials located in upper area of bundle toward upper epidermis comprised mainly of tracheary elements Circular midrib: central core of bundle Crescent midrib: upper portion of crescent conducts dissolved sugars located in lower portion of bundle towards lower epidermis Circular midrib: surrounds xylem Crescent midrib: lower portion of crescent

INSECTIVOROUS PLANTS trap and reduce organisms to

nitrogen sources with digestive enzymes Passive Traps incapable of movement (e,g, pitcher plant) Active Traps move during capture (e.g. Venus flytrap)

o Xylem

H.

INCREASED PHOTOSYNTHESIS
o e.g. stipules of rose plant, petioles of Kaffir lime

o Phloem

ANATOMY
A. MAJOR TISSUES 1. EPIDERMIS
o o o o o o Rectangular non-chlorophyllous parenchyma consists of normal epidermal cells (thicker outside than inside) has stomata and trichomes may or may not be cutinized relatively transparent allows light to penetrate Transpiration water loss through epidermis cover adaxial portion of lamina normal epidermal cells has more stomata in aquatic plants Trichomes lower ambient temperature, protect from herbivory, prevent water loss may or may not be cutinized Trichomes prevent rapid air movement, slow water loss from stomata has more stomata in horizontal leaves (reduces water loss; cooler than U.E.) Large round parenchyma in longitudinal rows Responsible for folding and unrolling of leaves (response to changing water potential and leaf pressure)

o Upper Epidermis

o Bundle Sheath nonvascular cells that surround veins controls amount of water protects vascular tissues from damage o Bundle Sheath Extensions support bundle sheath and extends to both epidermises

2.

NON-KRANZ
o Has palisade and spongy mesophyll o Only one type of chloroplast (mesophyll) which is arranged centripetally

DICOT LEAF
1. Epidermis a. Upper Epidermis b. Lower Epidermis c. Bulliform Cells d. Stomata 2. Mesophyll a. Palisade Mesophyll b. Spongy Mesophyll 3. Vascular Bundles a. Bundle Parenchyma b. Bundle Sheath c. Bundle Sheath Extensions d. Xylem e. Phloem

MONOCOT LEAF
equal number of stomata

o Lower Epidermis

less stomata

more stomata

equal number of stomata

o Bulliform/Motor Cells

kidney-shaped guard cells

Dumbbell-shaped guard cells

ADAPTATIONS TO ENVIRONMENT
A. AQUATIC PLANTS
o o o Long petioles for flotation Large air spaces for buoyancy Air ducts as pathways for oxygen from leaves to underwater roots/stems Leaves are needle-like to survive winter; reduces water loss Sunken stomata cuticle

2.

MESOPHYLL
o o o o o o o consists of photosynthetic ground tissue loose arrangement of cells rapid diffusion of gases between upper and lower epidermises many intercellular spaces site of chloroplasts may or may not be differentiated Midrib: made of parenchyma (surrounds bundle) and collenchyma (beneath epidermis) perpendicular, elongated, columnar cells stacked closely together main site of photosynthesis Xerophytes: more layers (to increase protection against water loss) Vertical leaves: palisade on both sides Horizontal leaves: palisade near upper surface irregularly shaped aerenchyma with intercellular spaces directly covered by lower epidermis allows diffusion of gases photosynthesis may also occur Hydrophytes: large air spaces in between

upper

upper and lower may be absent or modified into simple parenchyma

collenchyma

B.

DESERT PLANTS
o o o

no midrib

o Palisade Mesophyll

parenchyma/sclerenchyma

SUMMARY OF DIFFERENC ES
DICOT LEAF
Appearance Orientation Petiole Venation Mesophyll Cross Section Guard Cells broad, flattened dorsiventral

MONOCOT LEAF
long, narrow isobilateral leaf sheath parallel (un)differentiated evenly spaced veins kidney-shaped/dumbbell-like

sclerenchymatous

netted differentiated veins seen also in longitudinal kidney-shaped

o Spongy Mesophyll