Hawai’i is the most isolated major island group in the world, built up by and of volcanos and accordingly unstable but with a remarkable diversity of ecological niches. This has led to a flora on the one hand disharmonic (only three native orchids and one native genus of palms; no Gymnosperms nor primitive flowering plant families), on the other hand one of the worlds finest and most interesting ones. Though the island group is nearest to North America, most of the native flora is of Malesian affinity. In a sense, the flora is poor; one or a few colonist(s) often gave rise to a number of more or less closely related endemic species, some of which often relatively young polymorphic ones. The last complete treatment of the Hawaiian flora was Hillebrand’s ‘Flora of the Hawaiian Islands’ (1888). Since then, much work has been done, with different authors often based upon a very different species concept. This led to often strongly varying numbers of endemic species. Whereas Hillebrand accepted 705 native species, recent estimates varied between 1394 and 20,000-30,000 respectively! The authors of the present manual have tried to keep this number as low as possible; with their own words: “The main contribution of the Manual to Hawaiian botany is in providing a species concept that is probably more realistic, more functional, and more relevant to the understanding of this unique flora than anything available since the works of Hillebrand and Rock.” The total number of species here accepted is 1817; 956 of these are considered to be native and of these 89% are endemic. The number of genera accepted is 216, 15% of which are still endemic, but several of these are expected to be merged in the future with extra-Hawaiian genera. A good example of the treatment of endemic variation is to be found under Cyrtandra (Gesneriaceae) with 53 species accepted.