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Are palms trees? Or maybe large, woody herbs?

Is multiple-stemmed paurotis a tree? It all depends on your definition.
Is multiple-stemmed paurotis a tree? It all depends on your definition. Fairchild Tropical Botanic Garden

In a past Miami Herald article, I called a young palm a sapling. A reader asked why I used the term sapling for a young palm. The term sapling is used only for “trees” and from what he’d read, palms are not trees. This brought up a very interesting question: Are palms trees? It all depends on how you define a tree, and none of these definitions gives a clear-cut answer.

The most common definition of a tree is a large, woody plant with a single main stem or trunk. Some palms easily fall in this category, while others do not. Most solitary, erect palms would be considered trees under this definition — royal palms, for example. However, erect, clumping palms, such as the striking red lipstick palm, would not be considered trees.

Defining a tree based on a single main stem causes a dilemma for the palms, since many palm species — including the paurotis palm, a Florida native — can be both solitary and clumping. According to this definition, some paurotis are trees while others are not.

This common definition clearly doesn’t suit the needs of plant biologists, so many plant industries have created their own definitions.

Botanists define trees narrowly, as woody plants with secondary growth. Palms lack secondary growth and wood. They create their tough, wood-like epidermis through primary thickening and lignification. According to the botanical definition, palms are not trees but large, woody herbs. For botanists studying classification of plants, this makes sense because palms are classified as herbs, like their close relatives: grasses, bamboos, bananas, and sedges.

While botanists define trees narrowly, ecologists define trees broadly. In ecology, a tree is any plant that functions as a tree: providing habitat and shade, producing leaves and flowers, stabilizing soil, maintaining biodiversity and helping with climate control.

If we follow this definition, all erect palms can be defined as trees. Almost all palms that we frequently see in the urban landscape can be defined as trees as well. Using the ecological definition makes it much easier to define trees. However, not all palms are ecologically trees; rattan palms are lianas (climbing, woody plants) and non-erect palms are rhizomatous herbs.

An alternative tree definition, used by foresters, is any plant that is above a certain height and can be used for lumber. If we follow this definition, some palms certainly are trees, including thatch palms, which are commonly used as timber.

However, many palms are shrubby and don’t fit this definition. Saw palmetto, needle palm and dwarf palmetto are clearly not timber trees.

This definition is the most narrow and most easily applied; it is very clear whether a plant is a tree or not. However, it is also the least convenient for an everyday definition. It is the most narrow and the least commonly used.

None of these definitions is truly functional for the palms. Since trees have so many conflicting definitions, define palms based on their individual architecture. Royals, coconuts, and oil palms are tall, solitary, erect palms. Rattan palms are climbing palms. Saw palmetto and needle palms are shrubby, multiple-stemmed palms. Instead of defining and classifying a palm on whether or not it is a tree, describe its habit and architecture. This is much more useful.

So, are palms trees? Some certainly are and fit the definitions — royals and coconuts for example. However, other palms fall short and can only be described as woody, shrubby herbs.

More important than whether palms are trees is how much do these definitions matter? Sometimes a definition is important. Usually, rigid definitions are not needed. Just enjoy your backyard beauties and leave your dictionary inside. 

Sara Edelman is the palm and cycad manager at Fairchild Tropical Botanic Garden.