Wood Anatomy and Timber Identification

Every timber examination begins by locating and preparing three cutting planes. The transverse section (TS) cuts across the grain, perpendicular to the long axis of the tree. It is the face you see on a log end and the most diagnostic plane for most hardwood characters: vessel arrangement, ring boundaries, parenchyma patterns, and ray width in cell numbers.

The radial longitudinal section (RLS) cuts through the center of the tree and shows rays in their full height, as vertical plates. This plane reveals ray height in cells, whether rays are homogeneous or heterogeneous in cell type, and the surface texture of vessel walls. The tangential longitudinal section (TLS) cuts across the rays and reveals ray shape in profile, spindle form, number of cell rows, and whether rays of different sizes are both present (multiseriate and uniseriate rays together indicate a bistoriate complement).

In routine forensic work, examiners prioritize the transverse section because it is the most information-dense and because most processed lumber has at least one cut face that approximates a TS. For a complete IAWA profile, all three sections are prepared from a softened and hand-sectioned block, stained with safranin or other dye to enhance contrast, and mounted on glass slides. In field screening, a jeweller's loupe at 10x magnification on a freshly sanded face can often resolve ring-porosity class and approximate ray width without any laboratory preparation at all.

Hardwoods are angiosperms, and the characters that distinguish them are borne in their xylem: the conducting vessels, the laterally oriented rays, and the living parenchyma cells that wrap around and between them. The IAWA Hardwood Feature List codes these into 163 numbered characters, each with defined states. An identification proceeds by coding an unknown specimen and querying a database.

• Vessel characters: porosity (ring-porous, semi-ring-porous, diffuse-porous), vessel grouping (solitary, pairs, radial multiples, clusters), vessel diameter and frequency per mm², tangential diameter, perforation plate type (simple vs. scalariform), and intervessel pit shape.
• Ray characters: width in cell rows (uniseriate = one cell wide; biseriate = two; multiseriate = many), ray height in cells, cell composition (homogeneous = all one type vs. heterogeneous = mixed upright and procumbent), and visible on TLS whether aggregate rays are present.
• Parenchyma pattern: vasicentric (immediately surrounding a vessel), aliform (wing-shaped extensions from vasicentric), confluent (aliform bands linking adjacent vessels), banded (independent from vessels), or diffuse (scattered single cells). This pattern is visible on TS and is highly diagnostic.

For softwoods (conifers such as cedars and pines), the system is different because there are no vessels. Identification relies on tracheid dimensions, ray composition, presence or absence of resin canals, and cross-field pit type between rays and tracheids. Softwood identification is generally faster because the genus-level characters are fewer and more distinct, but species separation within a genus like Pinus remains challenging.

InsideWood (insidewood.lib.ncsu.edu) was launched in 2004 and has been updated continuously since. An examiner codes an unknown specimen using IAWA hardwood feature numbers, enters the list into InsideWood's search interface, and receives a ranked list of species matches with reference photomicrographs. The database is peer-reviewed, citable, and contains specimens from herbarium voucher material with traceable provenance, which matters in court.

The workflow in a forensic laboratory typically runs as follows. A seizure arrives, often a consignment of furniture, flooring, or musical instrument blanks. The examiner takes a small sample (a few grams of offcut is usually sufficient), softens it in boiling water or polyethylene glycol, hand-sections at 15-25 micrometres with a sliding microtome, stains with safranin, and mounts on glass. The slide is examined under bright-field microscopy, characters are coded to IAWA, and InsideWood returns candidate species. A comparison microscopy step checks the photomicrographs against the specimen.

Macroscopic examination covers features visible to the naked eye or with a hand lens (10x): wood color, grain direction (straight, interlocked, wavy), texture (coarse vs. fine, determined by vessel diameter and ray size), odor (freshly sanded rosewoods have a characteristic rose fragrance), luster, and figure. Color is unreliable for identification because it fades and because a skilled forger can stain timber. Odor and grain texture are more reliable but still genus-level at best.

Microscopy adds resolution but also time. A field identification at a port using only macroscopic features may be sufficient for a preliminary hold, but a defensible court exhibit requires a microscopic assessment coded to IAWA features and compared against a reference database or herbarium material. Some jurisdictions require a second examiner to independently verify the identification before a charge is laid.

Round logs and rough-sawn planks are relatively easy to sample. The challenge scales with processing. Surfaced and polished flooring may have had the outermost 2-4 mm removed, obliterating surface features. Finger-jointed planks combine multiple short sections from multiple trees, possibly multiple species. Veneer at 0.5-2 mm thickness is sometimes too thin to section at all. Composite boards bind wood fiber in resin, destroying cell integrity.

• Surfaced lumber: Find an end-grain face, or use a sharp blade to expose a fresh transverse face. Avoid sawdust, which is too damaged for reliable IAWA coding.
• Turned objects (furniture legs, bowls): Grain direction is typically clear, but sampling without damage to the exhibit requires a small offcut from an inconspicuous face. Some jurisdictions allow minimally invasive core drilling.
• Musical instruments: Regulations under CITES allow instruments in personal possession with a Musical Instrument Certificate. Identification is still needed at manufacture. Acoustic guitars use Dalbergia for back and sides; even the shavings on a luthier's floor can be identified to genus.
• Very thin veneer or pulp products: Anatomy alone fails. DNA extraction from wood powder becomes the primary method. See the companion topic on DNA and isotope methods for timber.

Enforcement agencies in China, the United States (LACEY Act), and the European Union (EU Timber Regulation, now the EU Deforestation Regulation from 2023) have all funded capacity-building programs to place trained xylotomists at major import ports. The US Forest Service Forest Products Laboratory in Madison, Wisconsin, and the Thünen Institute in Hamburg are two reference laboratories that take casework submissions from partner agencies worldwide.

Within a genus like Dalbergia, anatomy can narrow the identification to a species group or to a set of candidate species, but separating Dalbergia latifolia (Indian rosewood) from Dalbergia sissoo (shisham) or Dalbergia spruceana (Amazonian rosewood) by anatomy alone is often impossible. The IAWA key will return multiple candidates. At that point anatomy hands off to molecular methods.

Geographic origin is even further beyond anatomy. A plank of Dalbergia latifolia cut in Karnataka and one cut in a protected forest in Sri Lanka are anatomically identical. CITES enforcement often hinges on geographic origin, because legal trade from one country may be prohibited from another. Stable isotope analysis and chloroplast microsatellite population genetics are the tools for that question. Anatomy certifies the genus and, where possible, the species. Isotopes and DNA certify the origin.