Hibiscadelphus distans

Hibiscadelphus distans (Kauai hau kuahiwi) is an extremely rare species of flowering plant in the mallow family, Malvaceae, that is endemic to the island of Kauaʻi in Hawaii. It is known as hau kuahiwi in Hawaiian, which means "upland Hibiscus tiliaceus."[2] It is a bush or small tree with heart-shaped leaves and yellow flowers and grows at between 1,000 and 1,800 feet (300 and 550 m) in the remnants of native dry forests. Despite its rarity, it is believed to be the only surviving species in the genus Hibiscadelphus which is only known from Hawaii, the other five species having recently become extinct in the wild, some being known from only a single plant.

Hibiscadelphus distans
Hibiscadelphus distans growing in Limahuli Garden and Preserve

Critically Endangered  (IUCN 3.1)[1]
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Malvales
Family: Malvaceae
Genus: Hibiscadelphus
Species:
H. distans
Binomial name
Hibiscadelphus distans
Bishop & Herbst, 1973

Description

Hibiscadelphus distans is a shrub or small tree up to 5 m (16 ft) tall[3] with smooth bark and a rounded crown.[2] The heart-shaped leaves are 4–10 cm (1.6–3.9 in) in length and have rounded serrations on the margins and stellate trichomes (star-shaped hairs) on the upper on lower surfaces. The flowers are 3–4 cm (1.2–1.6 in) long and surrounded by triangular bracts. The sepals form a calyx tube around the greenish yellow petals, which turn maroon as they age. The fruit is a 2.5 cm (1 in) long, 1.5 cm (1 in) wide capsule that is divided into five sections. Each section contains two seeds around 5 mm (0.20 in) long. The capsule dehisces when mature, releasing the seeds.[3]

Habitat

Hau kuahiwi is found within low to mid-elevations, between 1,000 and 1,800 feet (300 and 550 m) in highly degraded remnants of native dry forests. The substrate is basaltic bedrock overlain by dry, crumbly red-brown soil.[2] The current population exists in the Lower Koaiʻe Canyon, a tributary of Waimea Canyon, at an elevation of roughly 350 m (1,150 ft). Mean temperature in this habitat ranges from 18.5 to 25.7 °C (65.3 to 78.3 °F) and average annual rainfall is 150 cm (59 in).[4] Associated plants include kukui (Aleurites moluccana), ʻāhinahina (Artemisia kauaiensis), alaheʻe (Psydrax odorata), lama (Diospyros sandwicensis), nehe (Lipochaeta connata), kōlea (Myrsine spp.), kuluʻī (Nototrichium sandwicense), ʻālaʻa (Pouteria sandwicensis), Sacramento Bur (Triumfetta semitriloba) and āulu (Sapindus oahuensis).[5]

Conservation

There are only two known naturally occurring populations of H. distans, both in the Lower Koaiʻe Canyon area,[2] Puʻu Ka Pele Forest Reserve,[3] with an estimated 20 wild and 150 reintroduced trees. The original population, found in 1972, was located in Koaiʻe Canyon within the State-owned Nā Pali Kona Forest Reserve. In 1989, this population was destroyed by a landslide.[2] A second population of fifty trees in the Hipalau Valley was destroyed in 1992 by Hurricane Iniki.[5] Two botanical gardens in Hawaii have cultivated this plant species: McBryde Garden (National Tropical Botanical Garden) on Kauaʻi[3] and Waimea Valley on Oʻahu.[6]

Despite the extreme rarity of H. distans, it actually has the largest wild population of any Hibiscadelphus species. Five of the other six species are extinct or extinct in the wild[7] (four were only ever known from a single wild tree), the exception being H. woodii (also from Kauaʻi), which is known from only four individuals.

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References
  1. Clark, M. (2016). "Hibiscadelphus distans". IUCN Red List of Threatened Species. 2016: e.T30930A83801583. doi:10.2305/IUCN.UK.2016-2.RLTS.T30930A83801583.en.
  2. "Recovery Plan for Hibiscadelphus distans". Endangered Species in the Pacific Islands. United States Fish and Wildlife Service. 2009-04-27. Retrieved 2009-11-18.
  3. "Hibiscadelphus distans (Malvaceae)". Meet the Plants. National Tropical Botanical Garden. Retrieved 2009-11-18.
  4. "Species HAU KUAHIWI, KAUAI". Endangered Species Information System. Virginia Tech. 1996-10-13. Archived from the original on 2006-02-10. Retrieved 2009-11-18.
  5. "Hibiscadelphus distans". CPC National Collection Plant Profiles. Center for Plant Conservation. 2008-07-28. Archived from the original on 2010-10-28. Retrieved 2009-11-18.
  6. "Projects on Kauai". Rare Plant Conservation in Hawaii. Hawaii Department of Land and Natural Resources. Retrieved 2009-11-18.
  7. Wood, K.R. (Spring 1992). "New Hibiscadelphus found on Kauai" (PDF). Hawaii's Forests and Wildlife. Hawaii State Division of Forestry & Wildlife. 7 (1): 15. Archived from the original (PDF) on 2011-06-16.
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