Assemblage
Definition
The full community of diatom taxa present in a sample. The relative frequencies and absolute counts of species in an assemblage reflect the chemical and physical properties of the water body from which the sample was drawn.
- Measured as
- Counts or percentages of each taxon identified in the sample
- Used in two forensic disciplines
- Palynology (pollen and spore analysis) and diatom analysis (water and sediment trace evidence)
Common questions
What is an assemblage in forensic palynology?+
An assemblage is the complete collection of pollen and spore taxa (types) found in a sample, recorded as counts or percentages. Forensic examiners compare this assemblage against controls from the crime scene and background references to infer where the sample came from and match it to a suspect's clothing or shoes.
How do diatom assemblages reveal information about where a sample came from?+
The specific species of diatoms present in a sample, and how common each one is, reflect the chemical and physical conditions of the water body. By identifying the diatom assemblage and comparing it to reference collections, forensic scientists can link a sample to a particular lake, river, or wetland.
What is the difference between a sample and an assemblage?+
A sample is the physical material collected from a scene or person. The assemblage is the full community of organisms (pollen grains, diatoms, spores) that the scientist identifies and counts within that sample. One sample yields one assemblage.
Related terms
- Acetolysis
- Erdtman's 1934 extraction method. The sample is treated with a 9:1 mixture of acetic anhydride and concentrated sulphuric acid, which dissolves cellulose...
- Epitheca and hypotheca
- The two halves of the frustule. The epitheca (larger) fits over the hypotheca (smaller) like a lid over a box. During cell...
- Exotic marker
- A known quantity of an introduced pollen type (often Lycopodium clavatum spores from a calibrated tablet) added to a sample before processing....
- Frustule
- The silica cell wall of a diatom, composed of two overlapping valves (epitheca and hypotheca). Frustules are taxonomically distinctive, chemically resistant to...
- Pollen sum
- The total number of pollen and spore grains counted on a slide, used as the denominator for calculating the percentage of each...
- Provenance opinion
- The analyst's conclusion about the geographic or habitat origin of a pollen assemblage, expressed with explicit statement of confidence level, comparison data,...
- Raphe
- A longitudinal slit or canal in the valve of certain pennate diatoms that allows cytoplasmic streaming and active gliding movement across surfaces....
- Reference collection
- A curated library of verified specimens from known species, subspecies, and geographic populations used as comparators in forensic identification. The depth and...
- Sporopollenin vs. biogenic silica
- Pollen and spore walls are made of sporopollenin (a highly resistant biopolymer). Diatom frustules are made of biogenic opaline silica (SiO2·nH2O), a...
- Valve and girdle band
- The valve is the flat face of each frustule half, carrying the species-specific pore patterns used for identification. The girdle band is...
Explained in these topics
- Forensic Palynology Methods and SamplingThe full collection of pollen and spore taxa identified in a sample, expressed as counts or percentages. The assemblage is compared against scene controls and...
- Diatom Biology and TaxonomyThe full community of diatom taxa present in a sample. The relative frequencies and absolute counts of species in an assemblage reflect the chemical and physic...