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Wiliwili ( Erythrina sandwicensis) is a species of tree in the pea family, Fabaceae, that is Endemism to the Hawaiian Islands. It is the only species of Erythrina that naturally occurs there. It is typically found in Hawaiian tropical dry forests on leeward island slopes up to an elevation of .
Wiliwili means "repeatedly twisted" in the Hawaiian language and refers to the seedpods, which dehisce, or twist open, to reveal the seeds.
The wiliwili is summer (dry season) drought deciduous. The dry season usually begins in late April or in May, and trees in the wild typically lose all of their leaves before they bloom. Trees in cultivation may retain much of their foliage through Anthesis.George W. Staples and Derral R. Herbst. 2005. "A Tropical Garden Flora" Bishop Museum Press: Honolulu, HI, USA. The flowers appear in the first half of the dry season, from April through July. They form on horizontal or nearly horizontal that are long. The flower color may be orange, yellow, salmon, greenish or whitish. Sometimes all of these colors occur in a single population. The standard petal is erect, not enclosing the other petals. Like all of the erythrinas, the wiliwili is pollinated by .Anne Bruneau. 1996. "Phylogenetic and Biogeographical Patterns in Erythrina (Leguminosae: Phaseoleae) as Inferred from Morphological and Chloroplast DNA Characters". Systematic Botany 21(4):587-605. The horizontal raceme and the erect standard are adaptations to pollination by passerine birds.Anne Bruneau. 1997. "Evolution and Homology of Bird Pollination Syndromes in Erythrina (Leguminosae). American Journal of Botany 84(1):54-71. Many other erythrinas are pollinated by , which do not occur in Hawaii.
Pods develop and persist on the tree, with the seeds remaining attached long after the pods have opened. The seeds are dislodged by heavy downpours that generally start around November in the islands. Many seeds Germination quickly, and a well-established seedling can grow to in height before the start of the next dry season.
That the wiliwili bears spines is unusual for a species that has evolved in the isolated Hawaiian Islands, without the presence of or other large . Many plants in the islands have consequently evolved away the protection of spines. The wiliwili is thought to be closely related to E. tahitensis, a tree endemic to the Tahiti, and E. velutina, a widespread species found in tropical South America and the Caribbean.
The wiliwili is distinguished from the other seven cultivated species by a Legume with only one to three red or yellow-orange , which sink in water;Carlquist, S. 1966. The Biota of Long-Distance Dispersal. III. Loss of Dispersibility in the Hawaiian Flora. Brittonia 18(4):310-335 non-native Erythrina have pods with larger numbers of brown seeds, which float in water.
It was additionally reported in December 2005 that the Hawaiian wiliwili population was under immediate threat due to an infestation by a gall wasp, Quadrastichus erythrinae, which had been first reported in Hawaii in April of that year. This invasive species appears to have arrived in Hawaii via southern Taiwan, Singapore and southern China within only two years. This species was not previously known to science and was formally named and described in 2004.I.K. Kim, G. Delvare, and J. La Salle. 2004. "A new species of Quadrastichus (Hymenoptera: Eulophidae): A gall-inducing pest on Erythrina (Fabaceae)". Journal of Hymenoptera Research 13:243-249. It is thought to have originated in Africa, and the means of its rapid dispersal across South Asia, the Pacific, and southern North America is not understood.Daniel Rubinoff, Brenden S. Holland, Alexandra Shibata, Russell H. Messing, and Mark G. Wright. 2010. "Rapid Invasion Despite Lack of Genetic Variation in the Erythrina Gall Wasp (Quadrastichus erythrinae Kim)" Pacific Science 64(1):23-31. The majority of trees of introduced Erythrina species have died as a result of gall wasp infestation. Native wiliwili forests have also been hard hit, particularly Puu o Kali on the island of Maui - prior to 2001, the best remaining example of a Hawaiʻi low elevation dryland forest ecosystem. The USGS-Pacific Island Ecosystems Research Center study site now documents the destructive impact of two invasive insect species (African bruchid beetle Specularius impressithorax and erythrina gall wasp) on Erythrina sandwicensis.
A parasitoid wasp, Eurytoma erythrinae, was released by the Hawaii Department of Agriculture in December 2008 as a biocontrol to minimize the damaging effects of Quadrastichus. Eurytoma wasps lay their eggs in the created by Quadrastichus wasps. Eurytoma larvae hatch faster than Quadrastichus larvae, on which they exclusively feed. The introduction of Eurytoma has reduced the population of Quadrastichus to a point where the wiliwili trees no longer die, but still have a much reduced production of viable seeds. That's largely because Eurytoma larvae need to feed on multiple Quadrastichus to complete their development, and egg-laying female Eurytoma therefore ignore small isolated galls containing a single larva. The Hawaii Departments of Agriculture and of Land & Natural Resources therefore plan to introduce a second parasitoid wasp from Africa, Aprostocetus nitens. The smaller A. nityens completes its development feeding from a single Quadrastichus larva, and it is therefore expected to complement Eurytoma by targeting isolated larvae.
In 1786, in his book , Jean-Baptiste Lamarck Neologism the Botanical name Erythrina monosperma for a Fabaceae tree from India and Southeast Asia.Jean-Baptiste Lamarck. 1786. Encyclopédie Méthodique: Botanique 2(1):391-392. In: Encyclopédie Méthodique par ordre de matieres. (see External links below). That tree has been known as Butea monosperma ever since William Roxburgh created the genus Butea in 1795.
Unaware of Lamarck's name, Charles Gaudichaud-Beaupré created the name Erythrina monosperma for the Hawaiian Erythrina in 1830 in his book Voyage of the Uranus.Charles Gaudichaud-Beaupré. 1830. Voyage de l'Uranie. Botanique (full title: Voyage autour du Monde, entrepris par Ordre du Roi, . . . Execute sur les Corvettes de S.M. l'Uranie et la Physicienne . . . par M. Louis de Freycinet. Botanique . . .) page 486 and table 114.
In 1841, William Jackson Hooker and George Arnott used Gaudichaud's name in their book, The Botany of Captain Beechey's Voyage.William Jackson Hooker and George Arnott Walker-Arnott. 1841. The Botany of Captain Beechey's Voyage part 2, page 81. (see External links below).
Gaudichaud's name, Erythrina monosperma, was used by most of those who described the Hawaiian species of Erythrina throughout the nineteenth century, including William Hillebrand.William Hillebrand. 1888. Flora of the Hawaiian Islands:99. (reprinted by Lubrecht & Cramer in 1981). (see External links below.)
In 1932, Otto Degener created the name Erythrina sandwicensis to replace Erythrina monosperma. He stated no reason for the name change. He presented a more complete synonymy than the one given here. Erythrina sandwicensis is the name that has been used since 1932.
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