Angiosperms VPrimary Growth:

Leaves

Leaf Morphology

Leaves are arranged on stems in either an opposite, alternate, or whorled pattern

This arrangement is called the phyllotaxis

Most leaves are either simple or compound

A SIMPLE LEAF

External Leaf Morphology

The leaf blade is connected to the stem by the petiole

Other leaf parts include: base, margin, apex, venation

margin

apex

base

venation

petiole

Simple Leaves

Pinnately compound leaves are similar to ferns: leaflets attached along a rachis

Palmate leaves have leaflets attached at one point

CompoundLeaves

Simple vs. Compound Leaves

Axillary buds occur at the base of each leaf - not at the base of leaflets

The abscission layer forms at the base of the leaf’s petiole - not at the base of a leaflet

Leaflets are generally all produced in the same plane - leaves have a phyllotaxis

Internal Structure (eudicot)

Internal Structure (monocot)

Upper epidermis

Bulliform cells

Mesophyll Veins with

bundle sheath cells

Guard cells

Action of Bulliform Cells (open)

Action of Bulliform

Cells (closed)

Leaf Abscission Abscission takes

place at the base of the leaf (not leaflets)

Response to hormones triggered by environment changes

Two regions:– Separation layer– Protective layer

Variations and Uses Multiple epidermal layers Thick cuticles Many trichomes (African

violet) Stomata in sunken pits with

trichomes (xerophytes) Stomata only on the upper

surface (water lilies) Leaves modified to be tendrils

or spines

Variations and Uses (cont.)

Carnivorous plants (specialized for obtaining mineral nutrients in wet or mineral poor habitats)– Venus fly trap– Sundew– Pitcher plants

Sundew

Pitcher Plants

Variations andUses (cont.)

Leaves for human consumption or use as medicines, dyes, fibers, waxes and for smoking