Self-sterile A plant not capable of reproducing with its own pollen.
Semi-double A flower with only a few stamens converted to petals; a flower with less than twice the normal number of petals.
These are self-sterile hybrids. They can be grow by seed, but they will not produce any viable seeds to save. They are not truly seedless, but the seeds do not mature and remain, small, white and edible.
Self-sterile Two varieties are needed for pollination. Self-incompatible (self-unfruitful) Unable to produce fruit and seed when self-pollinated; requires cross-pollination from another cultivar.
Muscadines come in self-fertile and self-sterile lines. The best fruits are from the self-sterile vines; to assure pollination you have to grow a pollinizing vine, too.
Others are self-sterile, meaning they require pollen from another tree. Apples, pears, plums and cherries are a few species that generally require a pollenizer.
Dogwood shrub flowers are self-sterile, so they must be cross-pollinated to produce seed. Seeds need cold stratification for one to three months in order to germinate; they will remain viable in cold storage for four to eight years.
Self-unfruitful or self-sterile
Plants in which very little fruit will set
Varieties that set fruit with their own pollen
Varieties that will not set fruit even when cross-pollinated
Finally, you need to consider pollination - most apple trees are self-sterile and require the pollen from other apple trees in order to produce fruit. See the section on pollination for advice and guidance.
See also: Sterile, Planting, Plant, Flower, Water