A. Lamina (blade) - the expanded, photosynthetic portion
of the leaf
B. Petiole - the stalk of a leaf
1. Sessile - a leaf that lacks a petiole
C. Leaves may be simple or compound, i.e.
they may have one or more lamina
1. The individual laminas of a compound leaf are called leaflets
and they may be arranged either
a. palmately or
b. pinnately
2. A bud defines a leaf
a. Except for a brief period in the spring leaves have a bud in the
upper axil, where they attach to the stem
b. The key to determining whether or not a leaf is simple or compound
is to look for the this bud
c. Everything external to this bud is the leaf, regardless of how many
laminas there are
d. If more than one lamina then it is a compound leaf
D. Leave arrangement - leaves and leaflets may be arranged:
1. Opposite - 2 per node
2. Alternate - 1 per node
3. Whorled - more than 2 per node
E. Stipule - a small leaf-like structure where the leaf is
attached to the shoot
1. Some plants have them and some don't
2. They are especially conspicuous on rose bushes
F. Most monocots have sheathing leaf bases
G. Leaf characteristics are often used to aid in the identification of
plants. Diagnostic features include:
1. Leaf arrangement, e.g. opposite, alternate or whorled
2. Simple vs. compound
3. Lamina shape, base and apex (tip) shapes
4. Characteristics of the margins, e.g. toothed, lobed, entire, etc.
5. Different types of trichomes (hairs) may also be present on one or
both surfaces
H. Twig morphology (here
is a photo illustrating all the features)
The following are important characteristics of twigs:
1. terminal bud
2. terminal bud scale scars
3. lateral bud
4. bud scar
5. leaf scar
6. vascular bundle scar
7.
lenticel,
anatomy
