Species vary considerably in the longevity of individual plants, and this is very much affected by site factors such as the degree of moisture and nutrient stress. Under traditional garden cultivation, many herbaceous plants are far shorter lived due to the low-stress environments provided. Species such as Scobiosa columbaria may only live for three as opposed to 10 to 15 years as is typical on dry, infertile soils in semi-natural habitats. Being short lived is not necessarily a problem for persistence, providing that the species produces adequate seed that is capable of germination and establishment under the site conditions and management regime. This is discussed further in the section ‘Management to aid regeneration’. Some species are, however, almost immortal, essentially forming clonal communities as the rhizomes expand outwards. In most cases, plants with the latter growth-forms are more robust and are more likely to persist in the longer term.