Melicope is a genus of approximately 240 species of shrubs and trees belonging to the family Rutaceae, in the order Sapindales. The genus ranges from the Hawaiian Islands across the Pacific Ocean to tropical Asia, Australia, and New Zealand, with a particularly notable diversity of species in Hawaii.
Plants in the genus are characterized by simple or trifoliate leaves arranged in opposite pairs, sometimes in whorls. Flowers are borne in panicles and are typically bisexual, though most species are dioecious — individual plants bear either male or female flowers only. Each flower has four sepals, four petals, and four or eight stamens, with four (occasionally five) carpels fused at the base. The fruit consists of up to four follicles fused at the base, each containing one or two seeds.
Melicope was first formally described in 1775 by Johann Reinhold Forster and his son Georg Forster in their work Characteres Generum Plantarum. The type species is Melicope ternata, commonly known as wharangi in New Zealand. Molecular phylogenetic studies from 2007 onward revealed that the genus in its traditional circumscription was not monophyletic. The previously separate genus Platydesma, comprising four Hawaiian species, is now understood to be nested within Melicope and sister to all other Hawaiian species. Several New Caledonian genera — Comptonella, Dutaillyea, and Picrella — may also fall within Melicope under an expanded circumscription, though they are retained separately in the current 2021 Rutaceae subfamily classification, which places Melicope in the subfamily Zanthoxyloideae.
Melicope species play ecological roles as foodplants for various invertebrates, including caterpillars of the Ulysses butterfly (Papilio ulysses), which feed on M. elleryana, and larvae of belid weevils in the genus Proterhinus. The honey produced from the nectar of wharangi (M. ternata) is known to be toxic to humans.
Several Hawaiian Melicope species are listed as endangered under US federal law due to habitat loss and competition from invasive non-native plants, and a few species are already extinct.
Etymology
The name Melicope derives from the Greek words μελι (meli), meaning "honey," and κοπη (kope), meaning "a division," in reference to the honey-producing glands at the base of the ovary. The genus was formally established in 1775 by Johann Reinhold Forster and Georg Forster.
Distribution
Melicope is distributed from the Hawaiian Islands across the Pacific Ocean to tropical Asia, Australia, and New Zealand. The genus shows exceptional diversity in Hawaii, where numerous species are endemic. Several Pacific island groups and parts of Australasia also support native populations.
Ecology
Melicope species serve as host plants for a range of invertebrates. The caterpillars of the Ulysses butterfly (Papilio ulysses) feed on M. elleryana, while caterpillars of Thyrocopa moths are associated with M. clusiifolia. Larvae of belid weevils in the genus Proterhinus also feed on Melicope, typically targeting weakened, dying, or dead plant material. The nectar of wharangi (M. ternata) is known to produce toxic honey that can be harmful to humans.
Conservation
Several Hawaiian Melicope species are federally listed as endangered in the United States, primarily due to habitat loss and displacement by invasive non-native plants. A number of species are already considered extinct, making Melicope one of the plant genera with notable conservation concern in the Hawaiian Islands.
Taxonomy Notes
The genus was first described in 1775 by J.R. Forster and G. Forster, with Melicope ternata as the type species. Molecular phylogenetic evidence from 2007 onward demonstrated that the traditionally circumscribed Melicope was not monophyletic: Platydesma (four species, all Hawaiian) is nested within the genus. The 2021 Rutaceae subfamily classification places Melicope in subfamily Zanthoxyloideae, while noting that evidence does not yet support tribal-level placement. Genera Comptonella, Dutaillyea, Picrella, and possibly Dutailliopsis from New Caledonia, as well as the temperate Asian genus Tetradium (which has sometimes been merged into Melicope), remain subjects of ongoing circumscription debate.
