| Wiliwili | |
|---|---|
 | |
| Raceme ofwiliwili | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fabales |
| Family: | Fabaceae |
| Subfamily: | Faboideae |
| Genus: | Erythrina |
| Species: | E. sandwicensis |
| Binomial name | |
| Erythrina sandwicensis | |
Wiliwili (Erythrina sandwicensis) is aspecies of tree in the pea family,Fabaceae, that isendemic to theHawaiian Islands. It is the only species ofErythrina thatnaturally occurs there. It is typically found inHawaiian tropical dry forests onleeward island slopes up to an elevation of 600 m (2,000 ft).
Wiliwili means "repeatedly twisted" in theHawaiian language and refers to the seedpods, whichdehisce, or twist open, to reveal the seeds.
Wiliwili trees grow to a height of 4.5–9 m (15–30 ft) with a gnarled and stouttrunk that reaches 0.3–0.9 m (0.98–2.95 ft) in diameter. Thebark is smooth, slightly fissured, and covered in gray or blackspines up to 1 cm (0.39 in) in length. The bark on the main trunk of mature trees has a distinct orange cast,[2] which is caused by a terrestrialalga.[3]
Thewiliwili 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.[4] Trees in cultivation may retain much of their foliage throughblooming time.[5] The flowers appear in the first half of the dry season, from April through July.[2] They form on horizontal or nearly horizontalracemes that are 7.5–15 cm (3.0–5.9 in) long. The flower color may be orange, yellow, salmon, greenish or whitish.[2] Sometimes all of these colors occur in a single population. Thestandardpetal is erect, not enclosing the other petals. Like all of the erythrinas, the wiliwili ispollinated bybirds.[6] The horizontal raceme and the erect standard are adaptations to pollination bypasserine birds.[7] Many other erythrinas are pollinated byhummingbirds, 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 seedsgerminate quickly, and a well-established seedling can grow to 4 ft (1.2 m) in height before the start of the next dry season.
That thewiliwili bears spines is unusual for a species that hasevolved in the isolated Hawaiian Islands, without the presence ofungulates or other largeherbivores. Many plants in the islands have consequently evolved away the protection of spines. Thewiliwili is thought to be closely related toE. tahitensis, a tree endemic to theTahitian Archipelago, andE. velutina, a widespread species found in tropicalSouth America and theCaribbean.[4]
Wiliwili is occasionally seen incultivation in Hawaiʻi. It is easilypropagated fromcuttings.[8] Seven other species ofErythrina were under general cultivation in the Hawaiian Islands, but have been mostly extirpated by the alien gall wasp (seeConservation, below).[5] They were popular street trees in dry areas and windbreaks on fields. At least 80 others have been known inbotanical gardens there.[9] No non-native species ofErythrina is known to benaturalized in Hawaiʻi.[4]
Thewiliwili is distinguished from the other seven cultivated species by apod with only one to three red or yellow-orangeseeds, which sink in water;[10] non-nativeErythrina have pods with larger numbers of brown seeds, which float in water.[11]
Native Hawaiians made a number of items fromwiliwili wood because of its low density, such asmouo (fishing net floats),ama (outrigger canoe floats,[12] and extremely longpapa heʻe nalu (surfboards) calledolo.Olo, which averaged 18 feet (5.5 m), were exclusively ridden byaliʻi (royalty).[13] The wood was sometimes used for thewaʻa (hull) of outrigger canoes intended to be used near-shore, for recreation, or for training.[14] The shiny orange-redseeds were strung intolei.[2]
Like many other native species in Hawaiʻi, the wiliwili is threatened bycompetition withnon-native species that are free of thediseases,parasites, andherbivores that constrain them in their originalhabitats.
It was additionally reported in December 2005[15] that the Hawaiianwiliwili population was under immediate threat due to an infestation by agall wasp,[16]Quadrastichus erythrinae, which had been first reported in Hawaiʻi in April of that year. Thisinvasive species appears to have arrived in Hawaiʻi via southernTaiwan,Singapore and southernChina within only two years. This species was not previously known to science and was formally named and described in 2004.[17] It is thought to have originated in Africa, and the means of its rapiddispersal acrossSouth Asia, thePacific, and southernNorth America is not understood.[18] The majority of trees of introducedErythrina species have died as a result of gall wasp infestation. Nativewiliwili forests have also been hard hit, particularly Puʻu o Kali on the island ofMaui - prior to 2001, the best remaining example of aHawai'i 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 beetleSpecularius impressithorax and erythrina gall wasp) onErythrina sandwicensis.[19]
Aparasitoid wasp,Eurytoma erythrinae, was released by the Hawaiʻi Department of Agriculture in December 2008 as abiocontrol to minimize the damaging effects ofQuadrastichus.Eurytoma wasps lay their eggs in thegalls created byQuadrastichus wasps.Eurytoma larvae hatch faster thanQuadrastichus larvae, on which they exclusively feed.[20] The introduction ofEurytoma has reduced the population ofQuadrastichus to a point where the wiliwili trees no longer die, but still have a much reduced production of viable seeds. That's largely becauseEurytoma larvae need to feed on multipleQuadrastichus to complete their development, and egg-laying femaleEurytoma 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 smallerA. nityens completes its development feeding from a singleQuadrastichus larva, and it is therefore expected to complementEurytoma by targeting isolated larvae.[21]
The genusErythrina was established byLinnaeus in 1753 in his book,Species Plantarum.[22] The name means "red", a reference to the flower color of some of the well-known species.
In 1786, in his book Encyclopédie Méthodique: Botanique,Jean-Baptiste Lamarckoriginated thenameErythrina monosperma for aLeguminous tree fromIndia andSoutheast Asia.[23] That tree has been known asButea monosperma ever sinceWilliam Roxburgh created the genusButea in 1795.
Unaware of Lamarck's name,Charles Gaudichaud-Beaupré created the nameErythrina monosperma for the HawaiianErythrina in 1830 in his bookVoyage of the Uranus.[24]
In 1841,William Jackson Hooker andGeorge Arnott used Gaudichaud's name in their book,The Botany of Captain Beechey's Voyage.[25]
Gaudichaud's name,Erythrina monosperma, was used by most of those who described the Hawaiian species ofErythrina throughout the nineteenth century, includingWilliam Hillebrand.[26]
In 1932,Otto Degener created the nameErythrina sandwicensis to replaceErythrina monosperma.[8] He stated no reason for the name change. He presented a more completesynonymy than the one given here.Erythrina sandwicensis is the name that has been used since 1932.
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