Creating a Southern Maryland Type Collection

Charcoal and Wood Reference Collection

In creating a charcoal and wood reference collection, the first step was to accumulate an identified collection of woods from trees and shrubs at Jefferson Patterson Park and Museum in Calvert County, Maryland and then convert them to charcoal. Twenty five of the most commonly found hardwoods and softwoods are included in the Southern Maryland Type Collection. Transverse, radial and tangential surfaces of wood and charcoal are examined, as each type of wood has a characteristic structure. The samples were organized by scientific and common names and housed in specimen cabinets. Digital images were acquired and posted on this website.

What Plant Taxa are Covered?

Trees are divided into two broad classes, usually referred to as "hardwoods" and "softwoods."

Softwood: The term softwood is a general term for trees that produce cones (Gymnosperms), which usually have narrow, needle-shaped leaves and are evergreen. The term originated as a description of the hardness of the wood, although there are some hard softwoods like Heart Pine (Yellow Pine Group, Pinus spp.).

Hardwood: The term hardwood is a general term for flowering trees (Angiosperms) that usually have broad leaves that are shed (deciduous) and produce fruits. The term originated as a description of the hardness of the wood, although there are some soft hardwoods like Balsa (Ochroma spp.). Most imported tropical woods are hardwoods.

What Methods Were Used to Create the Type Collection?

Wood Sample Acquisition

Samples of dry, dead wood were extracted from branches or trunks of botanically identified trees, shrubs and vines on JPPM property. Samples were cut to manageable lengths (3 – 5 feet), bundled with bailing wire and labeled with Tyvec sheets attached. Samples were stored on outside, covered racks at the MAC Lab. Additional wood from taxa not on JPPM property was either collected off-site or procured from local hardwood dealers.

For the reference wood collection (JPPM), samples previously purchased from Colonial Hardwoods were verified microscopically, labeled, and accessioned. Additional samples were donated by Alden from the International Wood Collectors Society (IWCS), verified microscopically, labeled, and accessioned. Samples that were collected at JPPM were used exclusively for charcoal, unless they were non-commercial woods, shrubs or vines. The latter samples were cut to size (approx. 6” x 4’ x 1”), labeled, and accessioned.

Sample Preparation (Wood)

Specimens were trimmed to expose the radial, tangential, and transverse surfaces. For each of these planes, thin (15-20µ) sections were removed by hand with a single-edge razor blade. The sections were mounted on labeled microscope slides in a 1:1 solution of ethanol and glycerin. Slides were heated briefly on a hot plate to drive off air bubbles, and then examined under a compound microscope. Digital images were acquired and stored on the JPPM network.

Sample Preparation (Charcoal)

Samples of wood from the reference list were split into stake-size pieces for carbonization. They were placed over hot coals in BBQ grills with air tight lids and allowed to burn until about 80% consumed. At this point, the lids were placed on the grill and all vents closed. The ovens were opened the next day and the wood that was reduced to charcoal was placed in labeled ziplock bags. The taxa were accessioned into the charcoal collection and placed in the reference cabinet. Samples were arranged alphabetically by scientific name.

Samples were broken by hand, exposing the transverse surface first, then the tangential and radial surfaces second, if possible. Broken surfaces were examined under a dissecting type microscope that magnifies to about 300X with good resolution. Parts of the sample-fragments with the largest surfaces were placed on a dish containing sand. Sand is used to stabilize of the charcoal fragments for viewing. The sand is slightly moistened with glycerin to increase cohesion of sand grains and decrease the adhesion of the fragment to the sand-mass. Digital images were acquired and stored on JPPM network. After identification, sub-samples were returned to their bags and cataloged alphabetically by scientific name and curated in the MAC Lab paleobotanical study collection.

Method of Identification

The most efficient way to identify charcoal is by examining freshly fractured surfaces (end-grain, radial and tangential) using reflected light. Wood samples were identified prior to carbonization using memory, experience and standard microscopical wood keys and descriptions (Kukachka, 1960 for softwoods; Panshin & DeZeeuw, 1980 for hardwoods). Trade or common names are from Little (1979). Species designations were deduced using present tree distributions and range maps (Alden, 1995 & 1997; Elias, 1980, Gleason & Cronsquist, 1963; Little, 1979).

Limitations (Levels of Determination)

Microscopic wood & charcoal identification from archaeological contexts has limitations not always apparent to researchers. These limitations are based on many factors, including the size of the sample, the level that one looks at the sample (i.e. microscopic) and the evolutionary conservative nature of wood & charcoal with respect to species determination.

The hierarchy of plants is based on a taxonomic system developed by Carl Linnaeus (1707-1778), where each specific type of plant is given a binomial (“two-names”) the genus (like our family names, e.g. Smith) and a species name (like our first names, e.g. John). The Linnaean binomial is the preferred term used when conversing about wood, unless a well accepted trade name (the most typical “common name”) is assumed. The binomial is italicized, with the genus first and the species epithet second (e.g. Eastern White Pine is Pinus strobus). When one refers to an unknown species the term “sp.” is used and when one is referring to more than one species in a genus, the plural “spp.” is used. Similar genera are grouped into Families (ending in –aceae), similar families into Orders, similar orders into Classes, and similar classes into Divisions. Some individual species of plants, trees or woods can have numerous common names, while a particular common name can have numerous species associated with it. On this website, the binomial name is given, as well as accepted common names.

Determination of Genus

When people think of types of wood, they generally are thinking in terms Pine, Oak, Maple, Spruce, etc., which describe genera of trees (Pinus, Quercus, Acer, and Picea, respectively). Even with small samples, identification of wood & charcoal to the genus level is usually very accurate.

Determination of Species Groups

Species groups are groups of species, within a genus, that have anatomical similarity. For instance, the Pines (Pinus spp.) can be grouped into the Red Pine Group, White Pine Group and Yellow Pine Group. The Oaks (Quercus spp.) contain the Red (Erythrobalanus) and White (Leucobalanus) Groups and the Maples (Acer spp.) have species that separate into the Hard and Soft Groups.

Determination of Species

The microscopic determination of wood & charcoal to the species level is usually not possible. These limitations are based on the evolutionary conservative nature of wood. Species of wood (trees, and plants in general) have been determined in the past from the number, size, shape and orientation of external features, such as reproductive structures (flowers, fruits, cones), foliar structures (leaves or needles) or other parts of the plant like bark or branch morphology. These characteristics are rarely present in objects made of wood & charcoal. Other identifying techniques, such as DNA analysis, cannot be used either because of a lack of DNA in heartwood and potential contamination of archaeological wood materials.

Charcoal

All types of wood were burned (branches, roots, and shrubs in addition to commercial species). There are no keys for charcoal identification or for woody branches. There are no comprehensive keys for non-commercial trees and shrubs. Wood samples that have been turned to charcoal have lost characteristics important for accurate identification. There are no differences with respect to weight, density, hardness or color once wood has been charred. Cellular characters are more difficult to discern using reflected light microscopy and the material has lost most color contrast in comparison to wood examined with a compound microscope. Sample sizes of charcoal from archaeological contexts are usually smaller than wood samples from industrial contexts. Most identification keys are based on large samples from commercially important trees. Historically all types of wood were burned. There are no comprehensive identifying keys for charcoal, woody branches, or non-commercial trees and shrubs. Carbonization causes changes or destruction of diagnostic characteristics needed for accurate identification, wuch as color and cellular characteristics. Additionally, archaeological sample sizes are usually much smaller than modern wood samples, which existing identification keys are based on.