This BioProvince (as defined by Armen Takhtajan) comprises the Hawaiian Islands and Johnston Atoll. Situated in the mid-Pacific it is the World’s most isolated bioprovince being some 3765 km from the nearest continental land mass. Apart from the coral atolls, the islands have a volcanic lithology with two still active volcanoes on Hawaii. The volcanic Islands are the exposed summits of seafloor mountains or seamounts that have formed over the past 70 million years or so as the Pacific Lithospheric Plate has moved to the northwest over a stationary magmatic hot spot in the mantle. Situated mostly in the topics, they experience a warm tropical climate and lying within the wet trade wind belt they receive large amounts of precipitation. Nevertheless, there are very steep rainfall gradients with annual rainfall varying from 12 m on Mount Waialeale on Kauai (the wettest place on Earth) to just 518 mm on Mauna Loa (Hawaii). Despite North America being the nearest continent, the flora is mainly characterised by Indomalesian elements. In fact, species with Australian affinities are just as pronounced as the American components. Probably because of its extreme isolation the vascular plant flora is comparatively sparse with just 230 genera, but not surprisingly, it has exceptionally high levels of both generic and specific endemism, with some 39 endemic genera and about 2700 endemic species. This constitutes the highest level of endemism of any island, island group or continental area of comparable size in the World. Two plant groups that have undergone remarkable diversification are the Lobelioideae (a sub-family of the Campanulaceae) and the Asteraceae. Fleshy fruited lobelioids are rare in most parts of the World, but here they have diversified into four endemic genera: Clermontia, Cyanea, Delissea and Rollandia. They appeared to have evolved from a single orginal colonist probably from the Andes where fleshy-fruited lobelioids are well represented. Some species of Cyanea have now reached gigantic proportions and look superficially like palm-trees. Other endemic lobelioid genera include the strange monospecific Brighamia (Brighamia insignis) with its tapered succulent stems bearing rosettes of leaves. Among the endemic Asteraceae are the magnificent silverswards and greenswards, which collectively form the genus Argyroxiphium. These produce tall flowering spikes and several are adapted to the harsh alpine climate where they experience brilliant sunshine in conditions of almost zero humidity and regular frosts. They can even grow on the cinder cones within the Crater of Haleakala.
The following accounts for this BioProvince have been written or will be written with particular reference to endemic and locally important species. Accounts available are displayed in green or yellow. Those displayed in red are either in the pipeline or awaiting expert contributions.
|Endemic Vascular Plant Flora|