Individual

In virtually all species, individuals differ genetically. However, there are a few interesting exceptions to this generalization. Populations of some plants may have no genetic variability because the species propagates by non-sexual (or vegetative) means. In such plants, genetically uniform populations (or clones) may develop. These represent a single genetic "individual." For example, extensive clones of trembling aspen (Populus tremuloides) can develop when new trees sprout from underground stems (or rhizomes). Such aspen clones can cover more than 100 acres (40 ha) and consist of tens of thousands of trees. In terms of total biomass, such aspen clones may represent the world's largest "individual" organisms. Another case involves the duckweed, Lemna minor, a tiny aquatic plant that grows on water surfaces. Duckweed propagates by growing buds on the edge of a single leaf. These buds grow and break off to produce "new" plants genetically identical to the parent. These interesting cases of asexual propagation are exceptional because most populations and species contain a great deal of genetic variation amongst their individuals.