Plants are used not only for aesthetic purposes but also for poisoning (suicidal, accidental, or homicidal) or as trace/transfer evidence in criminal and civil cases. Forensic botany comes into play when a crime is linked to plants. Hence, the utilization of plant science in matters related to law is referred to as forensic botany.
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What is Forensic Botany?
Forensic botany is an integration of botany or plant science and forensics. The botanical aspect is primarily associated with the anatomy and taxonomy that helps identify particular plant species. The forensic aspect deals with recognizing plant-based evidence at the crime scene, its collection, and proper processing to be admissible in a court of law.
Plant materials are considered useful crime evidence because the cell walls of plant cells, spores, and pollens are composed of strong compounds (e.g., cellulose, pectin, and sporopollenin), which remain resistant to destruction for a prolonged period.
In 1935, forensic botany was used for the first time to solve a crime (Lindbergh Case). This case involved the kidnapping of a young boy named Charles Lindbergh by Bruno Hauptmann. Arthur Koehler, an expert in wood anatomy, presented evidence related to a ladder. He pointed out that the ladder used in the kidnapping was homemade and one of the woods used to build the ladder was the same one found at Hauptmann's house. This evidence directly linked the suspect to the crime. Since then, forensic botany has been used to solve various crimes globally.
Principles Behind the Application of Forensic Botany
The application of botany for criminal investigation is based on two key principles. The first is Locard's exchange principle, which entails any contact between two objects results in an exchange of matter between them. Therefore, this principle suggests that physical evidence, including botanical trace evidence, could be used to establish a link between the crime scene, the criminal, and the victim.
Based on the first principle, the pollen grains found on the suspect's clothes or any other belonging are primarily compared to those collected from the crime site. If these two pollen grains turn out to be a match, forensic botanists can positively establish a link between the suspect and the crime.
The second principle is based on the utilization of forensic botany methods to identify the distribution of plant species worldwide. This approach is useful because different plant species require different environments, water availability, soil condition, and temperature to grow. This information could link the crime, the suspect, and the victim.
Branches of Forensic Botany
Various branches of forensic botany have helped uncover the identity of criminals. Some of these are discussed below:
Forensic Plant Morphology
Plant morphological analysis deals with studying its external features, such as leaves, stems, flowers, roots, and bark, which helps identify plant species. In addition, this branch of forensic botany is also involved with matching fragments of a leaf based on their external morphological features.
Forensic Plant Anatomy
This branch of forensic botany deals with the study of the internal structure of plants. The unique anatomical structures of a plant's leaves, roots, stems, and barks, can be observed through longitudinal or vertical sectioning. Plant anatomy not only helps in the identification of plant species but also in their classification.
Palynology deals with the study of pollen grains and spores. Pollen grains are easily transferable between two objects due to their small size and are resistant to an acidic environment. These acid-resistant microscopic plant materials help to deduce the presence of a particular person or object associated with the crime scene and link them to a geographical area. Pollen and spores are unique to a particular region or country.
Forensic dendrochronology deals with the study of the tree's growth rings, which helps predict the exact year in which the rings were formed. Different tree species have different patterns of ring formation, which are based on various factors, such as climatic conditions, the period over which the ring formation takes place, and the water content of the soil during the ring formation. In forensic science, determining the number of growth rings helps understand the period in which the crime occurred.
This branch of forensic botany detects the presence and types of diatoms on the victim's body or evidence samples collected from the crime site. Diatoms are microscopic algae whose cell walls are composed of transparent, opaline silica. These are found only in freshwater. A forensic limnologist compares diatoms in the suspected crime scene with those in the collected evidence samples.
Forensic Plant Systematics
This branch of forensic botany is associated with the process of plant classification into different classes and families based on their morphology and genetic characteristics.
As the name suggests, forensic ecology applies knowledge of the relationship between different plant and animal species in a particular habitat to solve a crime.
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How does Forensic Botany Help in Solving Crimes?
Forensic botany can be applied to solve a wide range of cases. For example, suppose pollen grains are found on a corpse and not at the crime site. This would indicate that the body was moved from one place to another.
Diatoms are highly useful evidence, particularly in cases related to drowning victims. It helps determine if the victim was placed in the water before or after death. In the case of accidental drowning, there would be asphyxiation, which could cause rapid water ingression through the respiratory tract and then through the pulmonary alveoli. Hence, in this case, diatoms would be found in the victim's internal organs, including the bone marrow and brain. In contrast, if the body were placed in water after death, diatoms would be only found in the respiratory tract and not in any internal organs.
The government of several countries has banned the logging of specific trees. Forensic dendrochronology helps to determine illegal logging. Forensic ecology is used to identify buried or concealed corpses based on the structural changes in the vegetation in the surrounding area.
- Avis-Riordan, K. (2020) Plant forensics: Cracking criminal cases. Royal Botanic Garden Kew. [Online] Available at: https://www.kew.org/read-and-watch/how-forensic-botany-plant-science-solve-crimes
- Forensic Botany and Its Applications. (2020) [Online] Available at: https://legaldesire.com/forensic-botany-and-its-applications/
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- Aquila, I. et al. (2014) The role of forensic botany in crime scene investigation: case report and review of literature. Journal of Forensic Sciences, 59(3).
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- Coyle, H. et al. (2005) Forensic botany: using plant evidence to aid in forensic death investigation. Croatian Medical Journal, 46(4).