Yes, some Plumeria varieties are self-sterile, meaning they cannot successfully self-pollinate and produce seeds. Self-sterile varieties require cross-pollination with a different Plumeria plant to achieve fertilization and seed formation. The inability to self-pollinate promotes genetic diversity within the species and encourages outcrossing with other Plumeria varieties or species. As a result, cross-pollination is essential for successful seed production in self-sterile Plumeria varieties.