The most extreme form of monoculture involves the cultivation of a single genotype of a crop species, to the exclusion of other genotypes and other species. (Note that a single genotype would mean that all of the crop plants are genetically uniform.) Genetic monocultures may be grown in cases where plant breeders have managed to develop uniform strains of plants that are optimally adapted for growth under certain environmental conditions. To practice this extreme type of monoculture, it must be possible to propagate the desired genotype using non-sexual means, such as cuttings, root grafts, or tillers. Seeds, in comparison, are genetically variable, although in intensive agriculture they may be derived from relatively narrow, inbred strains of variable species. Examples of agricultural species that can be propagated asexually and therefore can potentially be grown as genetic monocultures include: (1) sugarcane (Saccharum officinarum), which can be cultivated from rhizome cuttings, (2) bananas (Musa sapientum), which can be propagated from tillers, (3) tea (Thea sinensis), which can be grown from stem cuttings, (4) strawberries (Fragaria x ananassa), which can be cultivated using runners, and (5) apples (Malus pumila), cherries (Prunus avium), and other trees of the rose family, which can be propagated using root grafts.