Describe the structure and state the functions of leaves.

State the primary function of leaves – photosynthesis.

LEAF

LEAF FUNCTION primary function of leaves:

Main site of photosynthesis (food production) although this can take place in any areas that contain chlorophyll, e.g., aerial roots of orchids. Exit point of water (transpiration).

Describe: petiole, lamina, veins, and midrib. Leaf shape, colour and leaf arrangement on the stem – simple, compound (palmate, pinnate).

LEAF STRUCTURE

DICOT LEAF

MONOCOT LEAF

PETIOLE leaf stalk, connecting leaf lamina to the stem.

LAMINA leaf blade, main area of leaf.

MIDRIB central main vein on a dicot leaf.

LEAF VEIN network of vascular bundles on dicot leaf. Parallel veins on monocot. Bringing water and minerals up, taking products down.

LEAF MARGIN Edge of a leaf.

STIPULE Feature of a leaf.

LEAF SHAPE Leaf shape – monocot, long strap like; dicot variable. Types of leaves: Simple (see above) single entire leaf. Compound – palmate/pinnate, several blades. Palmate – radiating from one point – not to be confused with the Acer leaf shape. Pinnate – a linear shape.

Acer – palmately-lobed or palmatipartite

PINNATELY LOBED LEAF SHAPE Refers principally to: entire leaf Having lobes pinnately arranged on the central axis. Latin: pinna + lobus https://en.wikipedia.org/wiki/Glossary_of_leaf_morphology#/media/File:Leaf_morphology_Pennatilobé.svg

PALMATE LEAF SHAPE Refers principally to: entire leaf Palm-shaped, i.e., with lobes or leaflets stemming from the leaf base.[4] Latin: palmatus https://en.wikipedia.org/wiki/Glossary_of_leaf_morphology#/media/File:Leaf_morphology_palmate.png

LEAF COLOUR

Mostly shades of green due to forms of chlorophyll present in the leaf. Acts in photosynthesis, and also protects the leaf. Variegation in leaves can be caused by chimeral (some tissue not producing chlorophyll). Yellow edge: Elaeagnus x ebbingei “Gilt Edge”. Yellow patch in centre of leaf: Elaeagnus x ebbingei “Limelight”. Reflective/blister variegation (air under the epidermis): Pilea cadierei “Aluminium Plant”. Pigmentation – several different pigments in the leaf or overlapping one another: Chlorophyll alpha – green. Chlorophyll beta – green. Carotenoids – yellows/oranges. (3 involved in photosynthesis). Anthocyanins – red/purple/blue. Pathological – virus present in the leaves causing: Mosaic patterns – Abutilon “Cannington Peter”. Vein clearing – Pelargonium peltatum “Sussex Lace”. Spots – Ligularia tussilaginea “Aureo-maculata”.

LEAF ARRANGEMENT Arrangement of leaves around a stem.

ALTERNATE LEAF ARRANGEMENT

OPPOSITE LEAF ARRANGEMENT

Draw a dicotyledon leaf section to show the following components epidermis, xylem, phloem, veins, palisade & spongy mesophyll, cuticle, guard cells and stomata.

SPONGY MESOPHYLL

PALLISADE CELL

STOMATA

LEAF STOMATA Stomata Closure: Stomata are mostly found on the under surface of leaves and are the main exit point of water from the plant (gases: oxygen/carbon dioxide both in and out). They control water loss by closing at night (open during the day) also if the leaf wilts the stomata loses its turgidity and so will close (extreme mid-day heat can cause stomata to close).

GUARD CELL

LEAF GUARD CELL

Describe how leaves are adapted to perform other functions - storage/perennation by bulbs, (Narcissus and Lilium) and water storage (Sedum), protection by leaf spine (Berberis), climbing by tendrils (Lathyrus) and twining petioles (Clematis) and attraction of pollinators by bracts (Hydrangea).

LEAF ADAPTATION

Storage/perennation by bulbs (Narcissus and Lilium):

Water storage (Sedum) – thick, waxy, cuticle cells store water in the leaf.

Sedum spectabile “Autumn Joy”.

Leaf Adaptations Limiting Water Loss: Common in plants from warm or windy climate, RHS – Thick waxy cuticle to reduce evaporation, e.g., Echeveria elegans;

RHS – Reduced leaf surface area, conifer needles; Pinus sylvestris RHS – Leaves covered in hairs to keep humidity close to the area of the stomata; Salvia argentea

Having fewer stomata; Having deep or extensive root systems; Having light, silver/grey foliage to reflect heat; Sunken stomata;Leaves that roll with the stomata on the inside, some grasses, e.g., Festuca glauca; Structural adaptations, e.g., Spartium junceum (Spanish broom) has very small leaves but the stem is dark green and photosynthesises; Spines, e.g., Opuntia polyacantha.

Protection by leaf spine (Berberis):

Climbing by tendrils (Lathyrus odoratus):

Twisting petioles (Clematis):

LEAF PERENNATION

Storage/perennation by bulbs (Narcissus and Lilium):

BULB

Storage/perennation by bulbs (Narcissus and Lilium):

LEAF SPINE

LEAF PERENNATION

Storage/perennation by bulbs (Narcissus and Lilium):

SUCCULENT

SUCCULENT LEAF

SUCCULENT PLANT

TENDRIL

TWINING PETIOLE

LEAF BRACT Attraction of pollinators by bracts Hydrangea ‘Marisii’ or H. ‘Altona’