The first four were described on EI by the American expedition that arrived in 1886 aboard USS Mohican. Paymaster Thomson, and others, spent eleven days on the island, and they have done a lot of valuable work there. The fifth one, the taro, was described by Heyerdahl as growing on EI in a wild state even recently.
Botanists generally divide cultivated plants into two categories, cultigens, and cultivars.
These are the usual agricultural plants that we are all familiar with. They need cultivation, i.e. they are far removed from their natural state, and they depend on the humans for survival. Such plants normally cannot survive in the wild by themselves, because they will be overcome by the more resilient wild plants in the area. One example of such a plant is maize, which is totally dependent on the humans for its survival. So the distinction here is between plants which can be grown in gardens or live wild, and those which can only survive when tended by humans.