Hardwood Anatomy

 

In sharp contrast to the simple anatomy of softwoods, the hardwoods of the world exhibit a dazzling array of endgrain patterns and intricate motifs; and it’s in this complexity that the challenge (and joy) of wood identification really comes alive. An unknown hardwood sample could be just about anything under the sun, yet as each anatomical feature is considered, anything is narrowed down to something.

That is to say, throughout the identification process, the more observations that can be made and classified about a hardwood sample, the more and more the field of possible candidates narrows. Ultimately, the point is reached where no further refinements can be recorded, and either a clear identification emerges, or a handful of possibilities remain.

As discussed on the page The Truth Behind Wood Identification, a positive identification down to the species level isn’t always possible, but generally, anything can be narrowed down to a more descriptive something, and in many cases, the genus or family of the wood can usually be ascertained. To begin this process, the largest and most conspicuous anatomical elements are examined first.

 

In temperate zones, it’s not unusual for hardwood pores to correspond to the annual growing season, with larger pores forming a band or ring along the earlywood zone. This category of porosity is called ring-porous.

The second category—common in many tropical species—occurs when the pores are distributed evenly throughout the wood. (Growth rings may still be discernible through other cell types, such as parenchyma bands, or a change of color in the wood fibers, but the largest elements—the pores—will be spread out and diffused throughout the wood.) This category of porosity is called diffuse-porous.

Additionally, a third, intermediate arrangement is also seen, which is sometimes difficult to define. It includes wood that has pores that are generally evenly spaced but grade from large to small between growth rings, subtly suggesting growth boundaries. (Wood species with pores of a uniform size that are arranged in weak or broken bands are considered by some sources to be a part of this intermediate category as well.) This intermediate category of porosity is interchangeably called either semi-ring-porous orsemi-diffuse-porous; for simplicity’s sake, this group will be referred to as semi-ring-porous throughout this website.

In addition to the foundational three-fold categorization of the pores, there’s also a few other factors pertaining to pores to consider in hardwood identification.

 

Parenchyma

In a living tree, the parenchyma contained in the sapwood consists of living tissue that serves as storage cells. Technically, there are a few different types of parenchyma cells seen in wood, (such as those occurring radially in the rays), but far and away the most common type of cells that are designated specifically as parenchyma refer tolongitudinal or axial parenchyma, which are oriented along the length of the tree-trunk. All references to parenchyma in this website will be describing axial parenchyma.

Single parenchyma cells are typically too small to be seen individually, but when viewed as a whole, patterns and shapes emerge. Very infrequently, parenchyma is absent or hardly observable, but in most hardwood species, parenchyma forms unique and telling patterns that greatly aid in the identification process. In describing parenchyma, there are two main classifications.

Apotracheal parenchyma In order to understand this somewhat intimidating scientific term, it may help to consider the English word “trachea,” which refers to a tube or pipe (in this case, a wood pore). Combine this with the Greek prefix “apo,” which meansaway from or separate, and the meaning becomes clearer.

Apotracheal refers to parenchyma cells that occur separate from the pores. Apotracheal parenchyma can occur as single scattered cells, classified as diffuse parenchyma.These cells are too small to be seen without a microscope. However, in some wood species, several apotracheal parenchyma cells are joined or aggregated together, forming thin but visible tangential lines. This formation is known as diffuse-in-aggregates parenchyma.