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The arresting of the normal development of all cells except for those in the germ line, resulting in a sexually mature organism with juvenile characteristics. Such a process, producing large morphological changes, could result from comparatively small genetic changes affecting growth rate. It is a method by which one species may arise virtually instantaneously from another. For example, it is thought most likely that Lemna (duckweeds) evolved from the floating water plant Pistia in this manner because the seedlings of Pistia are very similar to the adult form of Lemna. At a more general level it is believed herbaceous plants originated from trees by neoteny. The resemblance of an adult organism to the juvenile forms of its ancestors is termed paedomorphosis. The arresting of development at a later stage may lead to large changes in the morphology of a particular organ. Thus the tubelike flower of Delphinium nudicaule, which resembles the buds of other Delphinium species, may have evolved in this manner.
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