Kind of leafs

The petiole is the part of the leaf that connects the blade, which is the wide part that we tend to recognize as the leaf itself, and the stem or branch. Thus, the leaves can be classified according to the petiole in this way:

• The petiolate leaves have a petiole that connects the blade to the plant. This petiole can have very different sizes depending on the specific characteristics of each plant.
• The sessile or seated leaves , on the other hand, do not have a petiole. In these cases, the blade arises directly from the stem or branch.

However, not all plants have to be exclusively petiolate or sessile leaves: there are some that have leaves of both types, depending on whether they are leaves on the stem or at the base.

As we explained above, the blade is the most recognizable part of what we usually call the leaf, the broad and generally smooth area. The way in which the blade divides or not is another type of classification of the leaves .

• Simple leaves have a blade that is either not split at all, or it is, but its divisions do not reach the main vein.
• The divided or compound leaves , on the other hand, show a blade that divides completely up to the main vein, giving the sensation of several blades joined by a single petiole.

Actually, the most correct thing is to say that we classify them according to the morphology or shape of the blade, and not the leaf itself. It is one of the most visual and easy to identify classifications. The types of leaves according to the shape of the blade are the following:

• Elliptical sheet: as the name indicates, they are those whose shape traces an ellipsis, that is, an elongated or deformed circumference.
• Lanceolate leaf: they are those whose blade shows a characteristic shape of a spearhead or simple arrowhead, with a wider base and a narrow and sharp point.
• Acicular leaf: the typical needles of most conifers, such as pine, are easy to recognize examples of this morphology.
• Oval blade: they are similar to ellipticals, but somewhat wider at the base and with a sharper point.
• Heart-shaped blade: similar to the way we usually represent hearts.
• Sagittate blade: this characteristic shape resembles the tip of a halberd or a divided arrow, with a central point and two others open to the sides.
• Linear leaf: These leaves look like ribbons, with straight, regular edges that extend. They tend to be narrow and long.

In the image you can see these shapes and some more.

In addition to the previous classification, the shape that the edge of the leaf blade takes can also be differentiated. Thus, the types of leaves according to the edge of these are:

• Whole leaf: also called smooth leaves, the edge of whose blade extends in an uninterrupted line and in a straight way or with a constant curve.
• Toothed blade: in these leaves, the blade takes the shape of saw teeth, which can be very different in size depending on the specific shape of each species.
• Lobed or lobed leaf : these leaves create very marked irregularities in their contour, with projections and recesses of pronounced curved shapes.
• Wavy leaves : they present curvatures in their outline, but in a softer and less pronounced way than in the lobed ones, without actually forming “arms”.

Three main types of leaves can be found according to their veins , differentiated in this way:

• Penninervia leaf: these are the leaves that have a main vein, from which all the secondary veins start. It is the typical form adopted by most of the leaves that are represented.
• Palminervia leaf: its name comes from the palm of the hand because of its similarity to it. From a central point the different nerves come out as if they were the fingers of the hand.
• Leaf parallelinervia: its ribs extend close to parallelism throughout the entire leaf.