Pollen morphology in Rubus (Rosaceae) and its taxonomic implications

Rubus is one of the most species-rich and most taxonomically challenging genera in Rosaceae. Pollen morphology of Rubus species has been described by many researchers but never in a comprehensive study. In this study, pollen morphology of 155 species and 13 varieties representing all 12 subgenera of Rubus was examined using scanning electron microscope to investigate whether pollen characters can help elucidate the challenging taxonomy in this genus. The results showed that the pollen grains of studied Rubus species are tricolporate, and pollen shape varies from suboblate, spheroidal, subprolate and prolate to perprolate. Exine ornamentation of examined pollen grains can be divided into six types and three subtypes. The pollen cluster analysis tree, which was performed using nine pollen characters, does not agree well with the traditional macromorphological classification and molecular phylogenetic trees based on DNA fragments. Except for subg. Chamaemorus and subg. Comaropsis, pollen morphology seems difficult to distinguish at subgeneric or sectional level, and consequently it lacks significant taxonomic value at these levels. Pollen morphology may not be considered a diagnostic feature for the division of subgenera and sections in Rubus. Though pollen morphology alone is not sufficient to elucidate or reconstruct the taxonomic relationships within Rubus, it can provide some useful information for the taxonomic treatment at specific level.

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