To Tree or Not to Tree

Is a palm tree not a tree? In categorizing plants and animals for the Everglades Ark Epicollect5 data base I was conflicted in assigning the characteristics of trees to palms. I have called them palm trees forever but they really look different from oak, olive or other trees. Checking out the definition of a tree resulted in an ambiguous answer.

Featured image: In a spin about palms

Definition of tree: From a technical standpoint, palms fit American Forests’ current definition of trees, as they are woody plants with an erect perennial stem or trunk, at least 9.5 inches in circumference at 4.5 feet above the ground. They also have a definitively formed crown of foliage and a height of at least 13 feet. 

This still didn’t satisfy my curiosity. I still wondered why they were so different. Here are photographs of tree aspects to show the physical differences:

Tree landscape view

Olive tree, rigid and arborized branches
standing adjacent to palm
Palm tipped by heavy wind storm

Leaf patterns

Central vein with alternating branched secondary veins
Radial symmetry of straight palm leaves with straight unbranching veins

Photomacrograph leaves

Here is a demonstration of reticular veining ~35X
All straight, parallel veining without branching ~35X

Photomicrograph of leaves

Branching veins becoming progressively smaller as they branch ~600X
Straight, parallel veins even at the microscopic level at ~800X

Common biology of both di and mono cotyledonous plants. Both have chloroplasts for metabolism and stoma

Stoma are more randomly disbursed in the leaf surface. The stoma are on the underside of the leaf in the dicot group ~800X
Xylem and phloem circulation and stoma for respiration. The stoma are on the upper side of the leaf ~800X

Tree roots

Broad and deep root system of dicotyledon, olive tree adjacent to monocotyledon palm.
Root ball of monocotyledon, palm exposed by erosion

Tree cross sections

Tree rings show annual growth and suggest weather conditions. Specialized bark system.
No rings and no mechanism to repair. Bark is a remnant of leaf system.

Tree behavior to injury

Progressive but not yet complete healing of dicot tree

There is no mechanism for healing in palm trees.

Flowers

All dicots have five petals to their flowers

No petals but other monocots have three petals

Here is a list tabulating differences in the characteristics between the tree types.

Aspects:Palm True tree
Rootsshallow multiple small distributeddeep, branching with tap root
Trunkthe trunk is actually the stem which bendsthick, rigid
Branchesno branchesmultiple arborizations
Leavesveins begin at the base, run parallel to the length of the leaf, stoma on upper leaf surface central veins with multiple arborizations to leaf periphery, stoma on lower side of leaf
Outer surfacestumps of old growth leaves, no structured interior wood specialized bark covering wood
Trunk corefibrous without annular ringswoody, highly structured interior nutrient flow system
Interior structurefibrous with layered leavesorganized circulatory system, annular growth rings
Recoverycannot repair injury or diseasecan heal wound and fight disease
Developmentmonocotyledondicotyledon
DNAGrassTree
Comparison of plant distinguishing characteristics

A palm tree is really a palm grass.1 They are monocotyledons. Genetically they are similar to other grasses like bamboo. They are resistant to storm damage fracture because of their lack of a woody interior structure but are more subject to uprooting because of their shallow roots.

Grasses are flowering plants that are members of the monocot class that also include corn, rice, lilies, orchids and palms. Now that I understand what a palm is I can more freely post palm types, flowers and fruits. Later I will show the microscopic view of tree anatomy pointing out differences between monocots and dicots.

This subject opens a wide spectrum of ideas regarding plants. We have already broached the idea of cotyledons. There is much more to explore including the microscopic examination of cross sections of plants and their appendages or stems, roots and flowers as well as angiosperms vs gymnosperms and the role of sexual vs asexual reproduction and seed development.

The micrographs shown here are all done with simple direct bright field and transmitted light. Just wait until we get into cross sectional, stained, transmitted plane, and polarized light illumination!

The Epicollect5 database will be modified to reflect this altered view of classification.

  1. References:

Dicot vs monocot

Palm leaf anatomy

Plant vascular system

Plant leaf anatomy

#tree #palm #monocot #dicot #monocotyledon #dicotyledon #veins #stoma #annular rings #reticular veining #petals

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