There are a few more than 3,000 different species of palms, but they typically produce just a few basic patterns of leaves. Two of the most common leaf structures produced by palm trees are the Fan-type/Palmate (Figure 30) and the Feather-type/Pinnate (Figure 31).
Another leaf-related characteristic of interest with palms is whether or not they are “self-cleaning”. If the whole leaf separates cleanly from the trunk at the leaf base and falls off the tree, then it is called a self-cleaning palm. Usually there are “rings” around the length of the trunk of such palms, which mark the point of attachment (node) of a fallen leaf (Figure 32).
Palm leaves can be very large and heavy! Leaves of mature Royal Palms may weigh up to 100 pounds and the leaf sheath may be large enough to wrap around a person like a hot-dog in a bun, while the leaf blade may be ten feet long (Figure 33). They can fall without warning, although this most often happens during windy weather. You don’t want to be underneath one of these when it falls!
Garden visitors often ask if you can use the rings on palm tree trunks to tell how old the tree is. In a very general sense, one can get an approximation of tree age, but nowhere near the accuracy as with broadleaf trees from temperate climate zones. The palm produces external trunk rings at the same rate that it produces leaves, and leaf production is directly related to tree vigor, which, in turn is related to soil conditions (nutrient, water, and air availability, and climatic factors. One would have to study that kind of palm for several years and monitor leaf production per year. Then one could count the total number of rings along the trunk and divide by the average yearly leaf production and come up with an approximation of tree age. This would likely fall short of its true age, because the rings formed by the leaves of the young seedling are obliterated by trunk expansion at its base.
With some palms, though, the leaf just dies and remains attached to the trunk, often for a long time, and then it may just rot and break off somewhere near the base of the old petiole or have to be cut off with a saw (Picture 34 and 35). This situation may result in increased maintenance costs in a landscape setting, if one wants a “clean” look to a palm that is not self-cleaning.
Coconut palms were very useful to the Hawaiian people (food, fiber, weaving, thatch, wood), and are found throughout the tropics. People who visit the tropics expect to see them (Figure 36 and 37).
Unfortunately, coconut palms can be dangerous to unwary people beneath them. The heavy fruit can fall at any time, and injure or even kill those who happen to be unlucky enough to be struck. In a hurricane, coconuts can become lethal wind-blown missiles. In cities where coconut trees are part of the city landscape, the coconuts are regularly pruned off the trees to prevent possible injury from falling coconuts, and warning signs are often placed beneath coconut trees in public places. Coconuts are dispersed around the tropics via ocean currents (and humans—they were brought to Hawaii by the Polynesians = canoe plants). A coconut will not sprout while it is floating, because the “water” inside it must not be moving for it to germinate. So, it has to wash up on the beach and lie still for a while before it will be able to sprout. This is an important survival mechanism for the coconut. The baby/embryonic coconut plant is found directly beneath one of the 3 “eyes” in the “nut”—the eye that is soft. Because this one eye is soft, the embryonic shoot can push through the eye-covering and grow out of the hard nut shell (Figure 38 and 39).
Fortunately for the coconut palm, it produces both male and female flowers in its inflorescence (flower-producing structure), and can produce viable coconuts (fruits, each containing a seed).
Come to the World Botanical Gardens and see examples of all of these and more with one of our fun and exciting garden tours!
Dr. Lanny Neel, Garden Director Emeritus, World Botanical Gardens