I. Cultivar versus Variety
Varieties often occur in nature and most varieties are true to type. That means the seedlings grown from a variety will also have the same unique characteristic of the parent plant. For example, there is a white flowering redbud that was found in nature. Its scientific name is Cercis canadensis var. alba. The varietal term “alba” means white. If you were to germinate seed from this variety, most, if not all would also be white flowering.
Cultivars are not necessarily true to type. In fact cultivar means “cultivated variety.” Therefore, a cultivar was selected and cultivated by humans. Some cultivars originate as sports or mutations on plants. Other cultivars could be hybrids of two plants. To propagate true-to-type clones, many cultivars must be propagated vegetatively through cuttings, grafting, and even tissue culture. Propagation by seed usually produces something different than the parent plant.
ref. Cultivar versus Variety | Horticulture and Home Pest News
II. True-To-Type Cultivars
All seeded plants produce seed that is mono-embryonic, and in the case of cultivars are not true to type. However, some of these plants also produce poly-embryonic seeds – either mixed in with the former in a multi-seeded fruit or occurring in some of the fruits of a single-seeded fruit species.
Caution: plants don’t label which are poly for your convenience. For each plant Genus, some study is necessary to determine which are which.
Here are two examples of fruits that produce poly-embryonic seeds:
Citrus – selected species will have at least a few in each fruit.
Mango – only a few cultivars produce poly-embryonic seed.