PALYNOLOGY AND SYSTEMATICS OF CUPHEA (LYTHRACEAE). I. MORPHOLOGY AND ULTRASTRUCTURE OF THE POLLEN WALL

A survey of pollen from 153 species of Cuphea has revealed a remarkable array of morphological forms. The survey involved light and electron microscope investigations of C. crassiflora, jorullensis, and koehneana to determine details of exine morphology, and a more general study of pollen from an additional 150 species. Comparison of pollen types within a single morphological category and within taxonomic groups (i.e., sections or subsections) indicates considerable variation at subgeneric levels. The genus is distinctly eurypalynous, and the extent to which pollen varies among the sections, subsections, species and varieties is probably exceeded by few genera of comparable size. The pollen is also variable within each taxon, but size studies of single-anther lactic acid preparations demonstrate the genus is not polymorphic, as in Lythrum, where pollen polymorphism is associated with heterostyly. The latter phenomenon is as yet unknown in Cuphea. These results reveal that pollen morphology constitutes an important and useful character for taxonomic studies of Cuphea.