The dicotyledonous leaf
A typical leaf of a dicotyledonous plant consists of two main parts :
• the blade
• the petiole
The blade is thin and expanded and is supported by a network of veins while the petiole is slender and connects the leaf to the stem.
The leaf blade varies greatly in shape and there are numerous terms to describe its general shape. These terms describe the leaf's general shape, apex, base, margin, and veins
general shape apex base margin veins
The leaf blade has two types of configuration. It may be in one unit, in which case the leaf is called a simple leaf, or it may be divided into numerous small parts that look like individual leaves and which form a compound leaf. It may be difficult to tell whether one is looking at a simple leaf or the leaflet (pinna) of a compound leaf. The distinction can be made by the fact that a leaf (simple or compound) has an axial bud between the petiole and the stem.
The petiole
The petiole of a leaf may vary considerably and can be long, short, rounded or flat. Some leaves have no petioles in which case they are said to be sessile. At the base of the petiole in many leaves are small leaf-like structures called stipules e.g. in peas, beans and roses. Between the petiole and the stem is a bud of a potential branch (an axial bud).
Leaves may be arranged on the stem in a variety of ways. The place on the stem from where the leaves grow is called a node and the part between the nodes is the internode. If only one leaf arises at a node the leaves are said to be alternate, if there are two leaves they are opposite and if there are more than two they are whorled.
Alternate Opposite Leaves in whorls
*note some items in the exam may be taken from the supplements posted
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