Pollen morphology of Erica L. and related genera and its taxonomic significance

Abstract

Pollen morphology of a total of 25 species of Erica (23 species) and its closely related genera Calluna (monotypic) and Daboecia (monotypic) was examined by means of light and scanning electron microscopy (SEM), or SEM alone. The pollen tetrads of E. multiflora and E. trimera ssp. keniensis, and monads of E. barbigeroides and E. recurvifolia, were examined with transmission electron microscopy to study the exine stratification. The quantitative features of Erica pollen have varied widely. However, the exine sculpture of Erica pollen is often characterised by the presence of numerous minute granules as secondary sculpture. Calluna pollen is characterised by irregular tetrads and perforated septum, and the Daboecia pollen tetrads by larger values of the D/d, P/E and 2f/D ratios. The P/E ratio and exine architecture showed distinct differences between Erica monads and tetrads. Among the Erica species having pollen tetrads, two distinctly different palynomorphological groups could be identified based on the 2f/D ratio. Two distinct groups could also be differentiated on the basis of the L/P ratio within the Erica species producing monads. Palynological characters, therefore, might be featured as a useful tool to clarify infrageneric classification system for the large genus Erica.