Angiosperms V Primary Growth: Leaves

Leaf Morphology n Leaves are arranged on stems in either an opposite, alternate, or whorled pattern n This arrangement is called the phyllotaxis n Most leaves are either simple or compound A SIMPLE LEAF

External Leaf Morphology n The leaf blade is connected to the stem by the petiole n Other leaf parts include: base, margin, apex, venation margin apex base venation petiole

Simple Leaves

n Pinnately compound leaves are similar to ferns: leaflets attached along a rachis n Palmate leaves have leaflets attached at one point Compound Leaves

Simple vs. Compound Leaves n Axillary buds occur at the base of each leaf - not at the base of leaflets n The abscission layer forms at the base of the leaf’s petiole - not at the base of a leaflet n Leaflets are generally all produced in the same plane - leaves have a phyllotaxis

Internal Structure (eudicot)

Internal Structure (monocot) n Upper epidermis n Bulliform cells n Mesophyll n Veins with bundle sheath cells n Guard cells

Action of Bulliform Cells (open)

Action of Bulliform Cells (closed)

Leaf Abscission n Abscission takes place at the base of the leaf (not leaflets) n Response to hormones triggered by environment changes n Two regions: – Separation layer – Protective layer

Variations and Uses n Multiple epidermal layers n Thick cuticles n Many trichomes (African violet) n Stomata in sunken pits with trichomes (xerophytes) n Stomata only on the upper surface (water lilies) n Leaves modified to be tendrils or spines

Variations and Uses (cont.) n Carnivorous plants (specialized for obtaining mineral nutrients in wet or mineral poor habitats) – Venus fly trap – Sundew – Pitcher plants

Sundew

Pitcher Plants

Variations and Uses (cont.) n Leaves for human consumption or use as medicines, dyes, fibers, waxes and for smoking