LeavesLeaves

Leaf HomologiesLeaf Homologies

IdentificationIdentification

Tree shapeTree shape

Leaf HomologiesLeaf Homologies

Each leaf has a very different shape and function, yet all are homologous structures, derived from a common ancestral form.

What are Homologies?What are Homologies?

Shared similarities between organisms Shared similarities between organisms that are derived from common ancestors that are derived from common ancestors

Broadleaf or Conifer?Broadleaf or Conifer?

BROADLEAF (tree with leaves that are thin, flat & usually shed annually)

CONIFER (tree that bears cones and has needle-like or scale-like leaves)

ConifersConifers

Needle-likeNeedle-like SINGLY

FLAT length

SQUARE or 4-SIDED

Color BUNDLES OR

CLUSTERS DECIDUOUS EVERGREEN

# of needles held in BUNDLES

Scale-like Scale-like &&

Awl –likeAwl –like

Broadleaf TreesBroadleaf Trees

What external features can help What external features can help identify leaves / trees?identify leaves / trees?

Leaf shapeLeaf shape Leaf arrangementLeaf arrangement Leaf divisionLeaf division VenationVenation Tree shapeTree shape

Leaf shapeLeaf shape

Leaf arrangementsLeaf arrangements

Alternate

Each node has one leaf

Whorled

One node producing three or more leaves

Basal

Leaves originating in a cluster at the stem’s base

Opposite

Two nodes opposite each other on the stem, one leaf arising from each node

Leaf Arrangement—Opposite vs. Alternate

Leaf marginsLeaf margins

What is a leaf margin???

The MARGIN of a leaf is the leaf edge.

Some broadleaf trees have leaves with smooth edges or ENTIRE MARGINS.

Some broadleaf trees have LOBED LEAVES,

leaves with projections that shape the edge of the leaf.

Some broadleaf trees have TOOTHED MARGINS

or

Serratedcharacterized by a saw-like edge on

the leaf.

Leaf DivisionSimple vs. Compound Leaves. What is a leaflet?

Leaf divisionLeaf division

Simple Leaves•Single blade

Compound Leaves•Blade divided into leaflets

VenationVenation

1) Net 2)Parallel

Tree shapeTree shape