[2] Participating individuals or organisations undertake to collect and conserve living material of a particular group of plants, as well as research its history and cultivation.
[5] They may be individuals, botanic gardens, plant nurseries, local authority parks, or groups of people holding distributed collections.
[1] Some collections are composed of a taxonomic group, such as a single genus or species.
Others are defined by a horticultural group, such as cultivars with particular foliage characteristics or plants collected by a certain historical figure.
[4] There may be multiple collections covering the same plant group, which reduces the risk of rare plants being lost from extreme climatic events.