Tell One Wood from Another: Basic Wood Anatomy

Introduction

As a long-time woodworker, I enjoy being able to tell one wood from another. In the process of learning how to do that, I’ve developed some knowledge of wood anatomy that I think will interest both biology students and woodworkers. There is an enormous variety of wood-anatomy characteristics; this article discusses a selection to spark interest rather than provide an exhaustive exposition. Because this is an introductory piece and doesn’t cover all of my limited knowledge, I have included references at the end for further reading.

I limit this article to characteristics that are readily discernible to the average woodworker in a shop, garage, or basement with minimal effort and no elaborate equipment. It usually comes as a surprise—even to long-term woodworkers—how much information is available from wood with only a small effort. I want to emphasize that all images in this article were taken of wood I processed in my garage using only a random orbital sander. This is not an elaborate process. See the process.

What this article covers

The most interesting, easily available characteristics are found in the end grain of temperate-zone hardwoods. When you look at the end grain of hardwoods, two primary attributes are of interest: the growth rings (including pore distribution within the rings) and the parenchyma. Pores are the little tubes the tree uses to move sap and nutrients, and parenchyma is another wood tissue that can be arranged in many different ways.

Three steps to identify wood by end grain

• Expose. Clean the end grain so you can see the characteristics clearly. I use a random orbital sander to clean the end grain (the process is shown on my how-to page): clean up end grain.
• Examine. Look at the characteristics with a 10X jeweler’s loupe or take close-up photographs. My camera gives about a 12X view for close-ups.
• Use. Compare what you see with reference sources. Links to helpful references are provided at the end of this article.

Annual growth rings and earlywood/latewood

Trees in temperate zones have growing seasons that start in spring and continue through summer and fall. This growth cycle produces annual growth rings composed of earlywood and latewood.

Growth ring count

Fast-growing trees have few growth rings per inch; slow-growing trees have many more. Ring count is a useful characteristic but can vary widely within a species, so it is often not a reliable species identifier.

Types of growth rings (porosity)

One fundamental attribute is the type of porosity—how pores are arranged relative to growth rings. The main types are:

• Ring-porous: Large earlywood pores that drop off quickly to smaller latewood pores.
• Semi ring-porous: Large earlywood pores that drop off gradually into smaller latewood pores.
• Semi diffuse-porous: Almost uniform pore distribution but with some thinning or smaller pores in latewood.
• Diffuse-porous: Uniform pores throughout the ring.

Rays

Rays are radial tissues that run from the center of the tree outward toward the bark. Two aspects matter for identification: ray height (size) and ray density (how many per inch). The image below shows categories of ray thickness.

Pore density

Pore density describes how many pores occur in a unit area. The general categories are shown here. “Uncountable” is a practical label—under a microscope one could count them, but for field identification that’s usually unnecessary.

Pore size

Pore size ranges from too small to see with a 10X loupe up to very large, visible pores (for example, in red oak). Many hardwoods show pore-size variation within a growth ring; the earlywood pores may be much larger than latewood pores. The image below shows a size range.

Pore multiples

Sometimes pores grow adjacent and share a cell wall; these are called pore “multiples.” Multiples commonly occur in groups of two or three and more rarely up to eight or nine. The orientation of these groups is significant: they can be radial, tangential, or random. The images below illustrate examples. Orientation: the center of the tree is at the bottom and the outside of the tree is at the top; bottom-to-top is radial and left-to-right is tangential.

Dendritic groups

“Dendritic” means tree-like; this pore arrangement loosely resembles branching tree limbs. There are no widely used formal sub-designations for dendritic groups, so the image below shows a convenient set of examples I use for comparison.

Wavy bands

Pores may also group into wavy bands—just as the name describes. The image below shows typical wavy bands.

Aliform parenchyma

“Aliform” means wing-shaped. Two parenchyma groupings fall into this category. The first is called wing-shaped aliform parenchyma (because it looks solidly wing-shaped); the other is lozenge-shaped. When present, parenchyma cells surround pores and extend to either side in one of the two forms shown here. A well-defined example can resemble a squadron of WWII fighter planes; the lozenge form looks a bit like a cough lozenge.

Other parenchyma types

The images below show several other parenchyma arrangements, often appearing as horizontal lines on an end grain face.

The characteristics above are only a sample—enough to show how identification can rely on combinations of traits.

End-grain examples

Here are small 1/4″ x 1/4″ end-grain cross-sections that illustrate combinations of the characteristics described above. Once you become familiar with these traits, identifying some woods can be straightforward (though not always). Note the variety in this batch:

References

Understanding Wood by Bruce Hoadley
Identifying Wood by Bruce Hoadley
Wood anatomy — an introduction
Extensive parenchyma discussion
Extensive growth ring discussion
Massive compilation of wood images and discussion (400+ species)
50,000+ images of wood anatomy (use botanical names)

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