The native plant highlight for this Parker Press posting is the immensely resilient and intensely beautiful wiliwili (Erythrina sandwicensis)
Scientific roots
Wiliwili’s genus Erythrina consists of over one hundred species distributed across the tropics and warm temperate areas, including the Americas, Africa, Southeast Asia, Australia, and parts of Polynesia. (1) Though there aren’t many studies on the phylogeny of Wiliwili, it’s likely that its ancestor came from the neotropics through ocean currents or birds. (2)
Interestingly, wiliwili is one of the only endemic Hawaiian species to have spines to protect themselves against herbivores. You may wonder, since Hawai’i doesn’t have any native herbivores, why would it have evolved spines? Interestingly, it’s likely that wiliwili retained this trait from its ancestor, even though many plant species lost the defense mechanisms of their ancestors once establishing themselves in Hawai’i.
Wiliwili Bark - Credit: Kai Garcia-Tobar Wiliwili spines - Credit Forest & Kim Starr
Ecology
Wiliwili is one of the most drought-tolerant trees in Hawai’i, thriving in the driest of locations like Waikoloa and the Kohala coast. Additionally, it is commonly the largest tree species (reaching heights of 50 feet in ideal conditions) (3) in Hawaiian dry forests. Part of the wiliwili’s success is due to its unique adaptation to drought: shedding all of its leaves and hibernating. By hibernating during the hottest summer months, wiliwili can conserve water while still photosynthesizing through its bark.
Wiliwili trees are critical in Hawaiian dry forests, as they contribute leaf litter to build soil, provide nectar to native birds and insects through their prolific flowering, stabilize soil to prevent erosion, and create a habitat for native species.
Canopy of Hawai’i’s largest Wiliwili, located in Waikoloa - Wiliwili growing in harsh conditions, located in Waikoloa -
Credit: Kai Garcia-Tobar Credit Kai Garcia-Tobar
Cultural importance
The name “Wiliwili” literally translates to “Twist twist”. Its name comes from the way in which its seed pods open by repeatedly twisting until its bright seeds are exposed and drop.
Early Hawaiians had many uses for wiliwili. Hawaiians used its lightweight wood for papa he’e nalu (surfboards), wa’a (canoes), and fishing gear. The flowers were used for lei and medicine. The seeds were used for permanent lei. Additionally, wiliwili were used as an indicator for ocean safety. Upon observing how the season in which wiliwili flowering overlapped with increased shark attacks, the proverb “Pua ka wiliwili, nanahu ka manō”, meaning “when the wiliwili flowers, the shark bites”, was created.
Threats
Wiliwili is currently considered “Vulnerable” by the IUCN Red List (4), meaning its populations are at risk. Wiliwili face many threats, including habitat destruction by development, fires, extreme drought, and irregular weather patterns. However, possibly the greatest threat was/still is the invasive Erythrina gall wasp (Quadrastichus erythrinae), a wasp the size of a grain of sand. It was first discovered in Hawai’i in 2005, and it quickly spread across all islands. The wasp attacks all healthy tissue in wiliwili, deforming some tissue enough to prevent it from forming new leaves, thus causing the tree to die. At the time, it was thought that this wasp could cause the extinction of the beloved wiliwili. Luckily, biologists at the Hawaii Invasive Species Council identified a wasp in Tanzania that parasitized the gall wasps. Eurytoma erythrinae was released in Hawai’i in 2008, and since then, the health of wiliwili populations has improved. (5) Though still facing many issues today, the wiliwili has dodged extinction’s bullet for now.
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