Palm trees are tropical to sub-tropical plants that come in a wide range of shapes and sizes. They have a few anatomical characteristics in common, one of the chief of which are the leaves. The foliage of a palm tree is called a frond. Most palms grow fronds from the crown (or top) of the plant. The fronds are one major identifying device, second only to the type of trunk the plant grows. Palm leaves come in four main types; pinnate, palmate, bipinnate and entire.
How Fronds Grow
Fronds can take three to five years to mature. A 2:1 ratio of juvenile to mature fronds ensures that there is a constant supply available to provide food to the tree. The bud area of the crown holds the developing fronds. As an old frond dies, a new one emerges. The new fronds emerge from the top of the crown so the mature older fronds are always those held at the bottom of the foliage like a skirt. Some palm trees are "self-cleaning," and the old fronds fall off; others require pruning to remove old growth.
Emerged Growth Habit
The way the fronds position themselves after they have emerged indicates the species of the palm. Some fronds hold themselves in clusters or tufts off the trunk. A very few palms actually branch out from the base, and fronds form there. Most fronds are arching and singular or aerial-branching. The fronds on these are arranged in regular intervals along the stem; when they fall off, they leave characteristic scars on the trunk.
Appearance of a Frond
A frond emerges folded up and comprises an area called the cabbage. In some smaller palm species, this part is an edible delicacy. After the young leaf unfurls, it presents with a thick stem that is notched or serrated, then the sheath and the petiole appear. Any of these areas can also bear spines. Some fronds are only inches long, while other are many feet across. The color of a frond depends on the species, but most are a waxy green with a gray or brownish-green tone on the underside. The fronds can be matte or shiny, thick or thin in composition. The petiole graduates to the separated ends of the foliage, which spread out in a fan shape.
Types of Fronds
Pinnate leaves are the most common form of frond. The foliage resembles a feather and is divided at the end into individual leaflets. There is a thick, central rib in pinnate leaves. In contrast, palmate leaves show up on the fan palms. The leaf parts are set in a circle and divide from a central area, radiating outward. Bipinnate fronds are unusual and resemble a fish tail. Entire leaves look like pinnate leaves but do not divide at the ends into individual leaf sections. Only five palms have entire leaves.