Genera of flowering plants that are endemic to oceanic islands are often of great biological interest. These groups represent adaptive complexes that confer distinction to the islands or archipelagos in which they are found, and this often results in a focus on their conservation. In recent decades, numerous molecular phylogenetic (and other evolutionary) studies have been done on island genera, hence providing much valuable new information on relationships and evolution of island groups. Genera restricted to oceanic islands derive evolutionarily from parental stocks usually in continental regions. These parental genera are often themselves evolutionarily successful, being particularly adept at dispersal, adaptation, and speciation. These immigrants to isolated oceanic islands derive from common ancestors of large and diverse parents or directly from within the lineages themselves. If in the latter case the island derivatives are treated at the generic level, then the parental genus becomes paraphyletic in a cladistic sense. In this circumstance there are three alternatives to classification of the island group: (1) treat both the island complex as a distinct holophyletic genus and the progenitor as a coordinate, but paraphyletic, genus; (2) submerge the island complex into the parental genus, perhaps at the subgeneric or sectional level, creating a larger holophyletic genus; or (3) divide the parental genus and island complex into a series of smaller genera in such a manner that all become holophyletic. A synthesis of recent investigations on 100 endemic island genera and relatives was completed in the Bonin Islands, Canary Islands, Galápagos Islands, Hawaiian Islands, Madeiran Islands, Robinson Crusoe Islands, and St. Helena. The results show that 64 genera are still accepted and remain uninvestigated or are seen as holophyletic in phylogenetic analyses. Seven have already been submerged based on non-cladistic results, and 29 are viewed as being nested within larger parental genera. Of this latter group, 15 of the genera are still being recognized at this time; six have been recommended as belonging within their parental genera; and eight have been formally transferred into the progenitor genera with combinations made. If further actions were to be taken based on strict holophyly, following the second alternative mentioned above, then these 29 genera would disappear as endemics in their islands or archipelagos. This would result in an overall average drop of 31.9% endemic genera in oceanic islands worldwide (based on the sample analyzed). With the third alternative, new generic concepts for the island and progenitor taxa would need to be worked out. Instead of recognizing genera on the basis of simple holophyly, genera should be based on cohesiveness, distinctness, and monophyly s.l. (i.e., including paraphyly and holophyly). A statistic is provided as a means for making these assessments quantitatively. The importance of unique and/or divergent character change for classification of island lineages is also stressed.