Botanical Evidence Collection and Preservation

The first rule at any scene with botanical evidence is not to collect immediately. Before anything is moved or touched, a photographic and written record of the scene must exist. For plant evidence this means photographing the spatial relationship between the body or object of interest and surrounding vegetation, recording which plant species are growing close to the scene, and noting the condition of the vegetation (seasonal state, leaf coverage, whether plants appear recently disturbed).

A scale bar in photographs matters more for botanical evidence than for many other evidence types because plant-community boundaries can shift over metres. A photo that shows whether the scene is inside or outside a canopy, or whether a grave is in a predominantly grassy versus forested patch, has direct interpretive value later.

• Photograph vegetation surrounding the area of interest at wide, medium, and close range.
• Note and photograph any disturbance to vegetation: broken stems, crushed plants, displaced leaf litter, or cleared patches.
• Record the GPS coordinates of the scene and collect a description of the plant community (dominant species, growth stage, canopy cover).
• Note the season and weather conditions, particularly recent rainfall or wind, which affect pollen deposition and seed dispersal.

Macrobotanical evidence, plant material visible to the naked eye, includes fallen leaves, seeds and fruit, twigs, and bark fragments. At a scene it may be found on the body, on clothing, in a vehicle, or on the ground around the area of interest. On a suspect or on submitted clothing it may be present in pockets, trapped in fabric weave, or stuck in hair.

1. Wear fresh gloves and change between exhibits
   Disposable nitrile gloves prevent transfer between samples. A single pair used for multiple exhibits can carry seeds or fragments from one to another.
2. Use clean forceps or a dry brush
   Collect visible fragments with forceps and place them directly into a clean paper fold inside a labelled paper bag. Avoid plastic bags for most macrobotanical material because moisture causes mould.
3. Collect an associated reference sample
   From the same area of the scene collect reference material: seeds, leaves, and twigs from the surrounding vegetation. Placed in a separate, clearly labelled bag, these provide the comparison baseline.
4. Package clothing as a whole exhibit
   When clothing is the primary botanical exhibit, do not shake or search it at the scene. Package it intact in a large paper bag or fold it in clean kraft paper to preserve in-situ positioning of seeds and pollen.

Pollen collection from clothing, hair, skin, and vehicles uses adhesive tape strips. Low-tack tape is applied to the surface, pressed lightly to lift particles without damaging underlying material, and then sealed inside a clean glass slide holder or plastic vial. The areas sampled must be selected carefully: collar and cuffs on a jacket, for example, accumulate pollen at face and hand height during walking through vegetation, making them the most diagnostic areas for provenance questions.

Pollen from soil at a scene is collected differently. A small trowel cuts a vertical column sample through the soil profile, or discrete horizon samples are taken. These samples are then sealed in clean vials and transported to the laboratory for extraction. Soil pollen profiles contain a stratigraphic record of past vegetation and can provide a minimum age for a burial context.

Wood evidence may present as fragments at a scene, as tool marks on a structural timber, or as charred material in a fire investigation. For anatomical identification the aim is to preserve a clean cross-section through the wood, which requires clean-cut sampling rather than breaking or crushing. A small electric saw with a clean blade, or a sharp bolster chisel, can cut a representative section from a structural member without introducing contamination from adjacent material.

Root evidence associated with buried remains requires particularly careful collection. Roots are sampled in relation to the bones or soil layers they are found growing through, and their growth direction, diameter, and attachment point are documented photographically before removal. The depth and context of root penetration through skeletal material is the primary data point for post-mortem interval estimation.

Aquatic and waterlogged botanical material must be kept wet from collection to laboratory. Drying destroys the cell structure of waterlogged wood and causes aquatic seeds to distort, making species identification impossible. Samples are sealed in water-filled vials or placed in damp moss inside a sealed bag, and processed promptly.

Packaging botanical evidence follows the same general principles as all forensic evidence: each sample in its own container, tamper-evident sealing, and a label that includes the exhibit reference number, date and time of collection, the collector's name, a description of the contents, and the collection location. The label must be written on the container itself, not only on a bag tied to it, because bags can become separated.

Every transfer of an exhibit between people must be documented with the recipient's name, date, and the purpose of the transfer. If an exhibit is analysed by an external laboratory, the submission letter, the lab's receipt, and the return documentation all form part of the chain.

A forensic botanist's identifications depend on their reference materials. For macrobotanical work this means access to a herbarium, a curated collection of pressed and dried specimens identified by specialists, where unknowns can be compared directly against named vouchers. The world's major herbaria, including the Royal Botanic Gardens at Kew in the UK and the Smithsonian National Herbarium in the US, hold millions of specimens and are accessible to researchers including forensic analysts.

For palynology the reference is a pollen slide collection: slides prepared from known plant species at known flowering times, mounted and curated in the same way as case slides. The breadth of a reference pollen collection directly limits the identifications that can be made. An analyst working in a region with unfamiliar flora must either build local reference collections before taking cases from that region or collaborate with a specialist who already has them.