Pollen size and aperture number are reported for nine North American species of Myriophyllum. For seven of these, scanning electron micrographs are provided. The wall sculpture of M. alterniflorum is microrugulate and that of eight other species is microverrucate. In M. exalbescens and M. tenellum, microvermcae develop late in pollen maturation. Myriophyllum farwellii, a species that flowers underwater, has asymmetrically arranged pores and variation in pore number. An estimated 90% of M. farwellii pollen, from collections made in 1975 and 1976, had collapsed: the apparently sterile grains suggest that this species is at least partly apomictic. A pollen key to the species is provided.