Chemical characterization and classification of pollen. 
We report on the in situ characterization of tree pollen molecular composition based on Raman spectroscopy.  Different from purification-based analysis, the nondestructive approach allows (i) to analyze various classes of molecules simultaneously at microscopic resolution and (ii) to acquire fingerprint-like chemical information that was used for the classification of pollen from different species.  Hierarchical cluster analysis of spectra from fresh pollen samples of 15 species partly related at the genus level and family level indicates separation of species based on the complete Raman spectral signature and yields classification in accord with biological systematics.  The results have implications for the further elucidation of pollen biochemistry and also for the development of chemistry-based online pollen identification methods.