Leaf Homologies Identification Tree shape Leaves Leaf Homologies Identification Tree shape

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

What are Homologies? Shared similarities between organisms that are derived from common ancestors

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)

Conifers Scale-like Awl –like Needle-like SINGLY & BUNDLES OR CLUSTERS FLAT length SQUARE or 4-SIDED Color BUNDLES OR CLUSTERS DECIDUOUS EVERGREEN # of needles held in BUNDLES

Broadleaf Trees

What external features can help identify leaves / trees? Leaf shape Leaf arrangement Leaf division Venation Tree shape

Leaf shape

Leaf arrangements Opposite Whorled Alternate Basal Two nodes opposite each other on the stem, one leaf arising from each node Whorled One node producing three or more leaves Alternate Each node has one leaf Basal Leaves originating in a cluster at the stem’s base

Leaf Arrangement—Opposite vs. Alternate

The MARGIN of a leaf is the leaf edge. Leaf 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 Serrated characterized by a saw-like edge on the leaf.

Leaf Division Simple vs. Compound Leaves. What is a leaflet?

Leaf division Simple Leaves Single blade Compound Leaves Blade divided into leaflets

Venation 1) Net 2)Parallel

Tree shape