Sexine and Nexine
Definition
The two layers of the pollen exine (outer wall). Sexine is the sculptured outer layer (spines, ridges, reticulum), nexine is the smoother inner layer. Together with apertures they form the diagnostic morphology used to identify pollen species.
- Sexine
- Sculptured outer exine layer (spines, ridges, reticulum)
- Nexine
- Smoother inner exine layer
- Combined with
- Apertures, for species identification
- Structure
- Two layers of the pollen exine wall
Common questions
Why does the sexine layer carry most of the diagnostic detail?+
Its surface sculpturing, such as spines, ridges, or reticulate patterns, varies distinctly between plant species and is what palynologists examine under the microscope to identify pollen source, while the nexine is comparatively featureless.
How does exine structure help forensic palynology beyond simple species identification?+
Because the exine wall is highly resistant to decay, its layered structure and sculpturing survive in soil, on clothing, or in sediment long after other plant material degrades, letting examiners link evidence to a location or season.
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...
- Aperture
- An opening in the pollen wall through which the pollen tube emerges. Classified by shape into pores (porate), furrows (colpate) and combined...
- Diatom
- A microscopic alga with a silica cell wall (frustule) bearing species-specific surface ornamentation. Diatoms are abundant in freshwater, marine, and brackish environments....
- Diatom Test for Drowning
- Acid digestion of bone marrow (femur or sternum) followed by microscopic examination for diatoms. Diatoms in marrow indicate that water was aspirated...
- Forensic Palynology
- The application of pollen and spore analysis to legal investigations. A forensic palynologist identifies the species composition of pollen assemblages from crime-scene...
- Frustule
- The silica cell wall of a diatom, composed of two overlapping valves (epitheca and hypotheca). Frustules are taxonomically distinctive, chemically resistant to...
- Pennate vs Centric
- The two morphological groups of diatoms. Pennate diatoms are elongate with bilateral symmetry (Naviculaceae, Pinnularia, Cymbella). Centric diatoms are circular with radial...