Hibiscadelphus is a genus of flowering plants that are endemic to Hawaii. It is known by the Native Hawaiians as hau kuahiwi which means "mountain Hibiscus". The Latin name Hibiscadelphus means "brother of Hibiscus". It is distinctive for its peculiar flowers, which do not fully open. Hibiscadelphus is in the family Malvaceae, subfamily Malvoideae. Several of the species in this small genus are presumed extinct. Description Hibiscadelphus was first described by Austrian-American botanist Joseph Rock in 1911 on the basis of the species Hibiscadelphus giffardianus. Species in this genus are large shrubs or small trees, up to tall, with nearly circular leaves. The genus is characterized by flowers that never open to the flat form of Hibiscus, but remain folded together in a tubular form. This is presumed to be an adaptation to pollination by honeycreepers. The fruits are rough capsules containing up to 15 hairy seeds. The lateness of its discovery by western botanists indicates that Hibiscadelphus was already rare by the time Europeans arrived in Hawaii. Four species - H. bombycinus, H. crucibracteatus, H. giffardianus, and H. wilderianus - were only ever known from a single individual in the wild. Today, four of the known species are extinct, two are extinct in the wild and persist only in cultivation, and only one (H. distans) has a small, highly endangered wild population. Although it has been suggested that poor pollination due to extinction of their honeycreeper pollinators is a factor, the abundant fruits and high germination rates of at least some species argues against this. The main reason is probably feeding on seeds by rats. This fits with a decline of the group that began long before the arrival of cats, mosquitoes, and avian malaria decimated honeycreeper populations, since the Polynesian rat arrived with the early Hawaiian settlers. The widespread destruction of dry forests, both before and after European contact, was also a major factor. Hibiscadelphus species †Hibiscadelphus bombycinus - Known from only one collection, before 1868, from Kawaihae, Hawaii. †Hibiscadelphus crucibracteatus - In 1981 a single tree was discovered on the slopes of the Puhielelu Ridge on Lānai at an altitude of . This tree died in 1985. Efforts to save the species failed because seeds did not germinate. Hibiscadelphus distans - Less than 200 wild individuals occur above the Koaie River on Kauai, but it sets abundant, fertile seeds in cultivation. Hibiscadelphus giffardianus - In 1910 Joseph