Hibiscus trees of the genus Hibiscadelphus are known only from the Hawaiian Islands, to which they are endemic. Like many Hawaiian plants and animals they have fared badly due to human activities, notably the introduction of non-native species that either outcompete indigenous species or modify their environment irreversibly. Of seven previously described species of Hibiscadelphus, four are believed to be extinct, two survive only in cultivation, while one only has two surviving wild populations, each of 15-20 individuals.
In a paper published in the journal Phytokeys on 25 July 2014, Hank Oppenheimer and Keahi Bustamente of the Plant Extinction Prevention Program at the Department of Botany at the University of Hawai'i, Manoa and Steven Perlman of the National Tropical Botanical Garden in Kalaheo, describe a new species of Hibiscadelphus from West Maui.
The new species is named Hibiscadelphus stellatus, meaning ‘star shaped’, a reference to the pattern of the hairs on its leaves which are arranged in star-shaped clumps, and the bracts which surround its flowers. Hibiscadelphus stellatus is a small tree reaching 3-6 m in height, with many branches and smooth bark.
Hibiscadelphus stellatus. (A) Habit. (B) Flowers and leaves. (C) View of bracts illustrating stellate arrangement. (D) Close-up of flower. Oppenheimer et al. (2014).
Hibiscadelphus stellatus was found growing only on steep rocky slopes at altitudes of between 800 m and 900 m; the slopes all had a windward aspect, and the trees were midslope, between the upper rim of a deep valley and a stream at its bottom, in areas of mosaic tree and shrubland with an open canopy, growing on volcanic basalt derived soils. The trees were observed in February and April, when they were producing buds, flowers, immature and mature fruit; the flowers opened in the middle of the day and produced abundant nectar.
Hibiscadelphus stellatus. (A) Habit. (B) Flower bud. (C) Surface of calyx showing stellate hairs. (D) Flower. (E) Surface of corolla showing two sizes of stellate hairs. (F) Fruit. (G) Longitudinal section of fruit showing seed. Oppenheimer et al. (2014).
Only three populations of Hibiscadelphus stellatus are known, comprising 25, 40 and 23 plants respectively. All three populations are within 400 m of one-another. Seeds were collected from twelve plants representing all three populations, and are being raised at the Olinda Rare Plant Facility on Maui, National Tropical Botanical Garden on Kaua`i and the Lyon Arboretum on O`ahu. The area where the trees was found is judged to be at risk of fire, draught and a variety of invasive species, including Rats, Mice, Slugs, Sand Weevils, Caterpillars, Goats, Pigs and fire-adapted Grasses (Grasses that can survive periodic burning, which kills native Hawaiian plants, thereby allowing the Grasses to spread and colonize new areas).
Distribution map showing known locations of Hibiscadelphus stellatus on West Maui. Oppenheimer et al. (2014).
Hibiscadelphus stellatus is judged to be Endangered under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species.
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