Ultrastructure studies of the pollen grains of Opuntia polyacantha reveal an elaborately sculptured ektexine but no endexine. The mature pollen cytoplasm is non-vacuolated, and contains plastids, starch granules, lipids, endoplasmic reticulum (ER), and relatively few other recognizable structures. Membranes and inclusions taken to be plasmalemmasomes were observed in the intine. Invaginations of the plasma membrane were also observed.