Nucellar embryony (notated Nu+) is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. During the development of seeds in plants that possess this genetic Trait, the nucellar tissue which surrounds the megagametophyte can produce additional embryos (polyembryony), which are genetically identical to the parent plant. These nucellar seedlings are clones of the parent. By contrast, zygotic seedlings are sexually produced and inherit genetic material from both parents. Zygotic and nucellar embryos can occur in the same seed, and a zygotic embryo can divide to produce multiple embryos.
Nucellar embryony is important to the citrus industry, as it allows for the production of uniform rootstock which yields consistent results in fruit production. However, this trait can interfere with progress in cross-breeding; most commercial scion varieties produce mainly nucellar seedlings which do not inherit any of the traits of the "father" plant.