CPC Plant Profile: `Ohai
Search / Plant Profile / Sesbania tomentosa
Plant Profile

`Ohai (Sesbania tomentosa)

Closeup of scarlet flower. Note the contrasting color of the bud. Photo Credit: Peter Van Dyke
Description
  • Global Rank: G2 - Imperiled
  • Legal Status: Federally Endangered
  • Family: Fabaceae
  • State: HI
  • Nature Serve ID: 147237
  • Date Inducted in National Collection: 05/28/1986

This plant produces amazing large red pea-like flowers that have helped to draw attention to the loss of species on the Hawaiian Islands. Sesbania tomentosa is the only endemic Hawaiian species in the genus and while its numbers have not reached the dire levels of some endemics, it faces several threats to its continued existence. According to the U.S. Fish and Wildlife Service, two populations of Sesbania tomentosa at Paomai and Mahana on Lanai were last seen in the mid-1950s. The axis deer, an introduced species native to Sri Lanka and India, is probably responsible for their disappearance. (USFWS 1993) These animals along with a long list of introduced game and domestic animals are threatening much of the native vegetation by trampling and consuming young individuals, destroying seeds and removing the bark from older plants. The removal of these animals from the Hawaiian Islands delicate natural habitats is considered essential for saving the Ohai and many other endangered native species. In an odd twist of fate, the Ohai has escaped from cultivation in Puerto Rico and may have a better chance of surviving there (NatureServe Explorer 2002). Sesbania tomentosa is most often a low-growing, silver-green sprawling shrub, occasionally a small tree that grows up to 6 meters tall. Its branches hold young leaflets that are covered with silky hairs. The flowers resemble pea flowers in form and vary in color from orange red, to salmon, scarlet, or rarely yellow. Branches may extend to 14 m. along the ground, with single plants covering a large area. (Wagner et al 1999)

Participating Institutions
Updates
Center for Plant Conservation
  • 08/19/2021
  • Orthodox Seed Banking

In 2021, CPC contracted National Tropical Botanical Garden to recollect seed from a population currently held in long term orthodox seed storage as part of an IMLS-funded seed longevity experiment. The National Laboratory for Genetic Resources Preservation will evaluate how germination tested viability and RNA Integrity of seed lots decline over time in storage.

Dustin Wolkis
  • 08/13/2021
  • Orthodox Seed Banking

Seeds of Sesbania tomentosa were collected for CPC-IMLS RIN study from the National Tropical Botanical Garden's Living Collection at the South Shore Visitors Center on 5 August 2021.

  • 09/28/2020
  • Reintroduction

Rock barriers were constructed to protect individuals from off-road vehicle traffic on O'ahu, and hundreds of individuals have been propagated and outplanted there. Rodent control has resulted in some natural seedling germination and survival there. On Moloka'i, a fenced exclosure protects one population of several hundred plants. Outplanting and rodent and weed control have been conducted in Hawai'i Volcanoes National Park, and plants have been outplanted on Kaua'i. (USFWS 1999)

  • 09/28/2020
  • Propagation Research

Propagation has been researched by Karin Lileen-Rosenberger (1998). Rock barriers were constructed to protect individuals from off-road vehicle traffic on O'ahu, and hundreds of individuals have been propagated and outplanted there. Rodent control has resulted in some natural seedling germination and survival there. On Moloka'i, a fenced exclosure protects one population of several hundred plants. Outplanting and rodent and weed control have been conducted in Hawai'i Volcanoes National Park, and plants have been outplanted on Kaua'i. (USFWS 1999)

  • 09/28/2020
  • Reproductive Research

Pollination biology has been studied by U.H. Manoa zoology student David Hopper (Hopper 2002 and USFWS 2002).

Nature Serve Biotics
  • 05/02/2017

Recorded from all of the main Hawaiian Islands in addition to the Northwestern Hawaiian Islands of Nihoa and Necker. Although originally widely distributed throughout the Hawaiian Islands, the species has declined and now exists only in relictual populations. The total number of naturally occurring individuals is believed be under 4,000. This species has been affected by the host of factors that have led to the decline of most dry lowland habitats and their native plant species: developement, agriculture, alien plants and animals, and fire. While reportedly present as an escape from cultivation in Puerto Rico and other tropical areas, these plants are not considered to be significant to the species' conservation.

Peter Van Dyke
  • 01/01/2010

Animals: Axis deer, goats, and cattle degrade the habitat and destroy plants. Weeds: Molasses grass smothers the plants and prevents new growth. Kiawe and koa haole compete for water and space, and buffelgrass encourages fire. Fire. The mix of dry gr

Peter Van Dyke
  • 01/01/2010

27 populations (USFWS 1999) 2120-3120 individuals (Breugmann 1997) Populations on Nihoa and Necker are within the Hawaii Island National Wildlife Refuge. The one population on Kaua'i is in a state park. On O'ahu, the single population is on state owned land. On Molokai, populations are on both state and private land. On Maui, populations occur on state owned and private land, and on a National Guard training area. The population on Kaho'olawe is on a state-owned seabird sanctuary. On Hawaii, populations are found on state and private land, and within Hawaii Volcanoes National Park. (USFWS 1999)

Peter Van Dyke
  • 01/01/2010

Pollination biology has been studied by U.H. Manoa zoology student David Hopper (Hopper 2002 and USFWS 2002). Propagation has been researched by Karin Lileen-Rosenberger (1998)

Peter Van Dyke
  • 01/01/2010

Rock barriers were constructed to protect individuals from off-road vehicle traffic on O'ahu, and hundreds of individuals have been propagated and outplanted there. Rodent control has resulted in some natural seedling germination and survival there. On Moloka'i, a fenced exclosure protects one population of several hundred plants. Outplanting and rodent and weed control have been conducted in Hawai'i Volcanoes National Park, and plants have been outplanted on Kaua'i. (USFWS 1999) In April, 2002, the U.S. Fish and Wildlife Service determined that a designation of critical habitat was prudent for this species. (USFWS 2002)

Peter Van Dyke
  • 01/01/2010

Rodent control needs to be practiced more widely. Off road vehicle traffic control is needed to protect plants in the South Point area of Hawai'i Island.

Peter Van Dyke
  • 01/01/2010

An effort to collect and store seeds from all 27 populations will require collaboration between agencies and gardens.

MORE

Be the first to post an update!

Photos
Nomenclature
Taxon Sesbania tomentosa
Authority Hook. & Arn.
Family Fabaceae
CPC Number 3946
ITIS 505189
USDA SETO3
Common Names 'ohai | Oahu riverhemp
Associated Scientific Names Sesbania tomentosa | Sesbania arborea | Sesbania hawaiiensis | Sesbania hobdyi | Sesbania tomentosa var. molokaiensis
Distribution S. tomentosa occurs on Kaua'i, O'ahu, Moloka'i, Kaho'olawe, Maui, and Hawai'i, and on the Northwestern Hawaiian Islands of Nihoa and Necker. (USFWS 1999).
State Rank
State State Rank
Hawaii S2
Habitat

Formerly, S. tomentosa occurred widely in lower elevation, dry habitats on all the main islands. Now relict populations are found on sandy beaches, dunes, soil pockets in lava, and along pond margins (Wagner et al. 1999). It occurs in coastal dry shrublands and grasslands, open ohia forests, and coastal dry cliffs (USFWS 1999). Native coastal plants found associated with S. tomentosa include; ilima (Sida fallax), naupaka kahakai (Scaevola sericea), pili (Heterpogon contortus), and aki (Sprobolus virginicus). Now most lowland dry areas where S. tomentosa persists are disturbed and heavily invaded by non-native plants, including molasses grass (Melinis minutiflora), buffelgrass (Cenchrus ciliaris), kiawe (Prosopis pallida) and koa haole (Leucaena leucocephala). (USFWS 1999)

Ecological Relationships

Although many insects visit the flowers of Sesbania, successful pollination is accomplished by native bees (Hylaeus spp.). Pollinator limitation may be a problem for populations on the island of Oahu. Other aspects of the plant's life history are not known. (Hopper 2002, USFWS 1999 & 2002)

Pollinators
Common Name Name in Text Association Type Source InteractionID
Bees
Masked bees Hylaeus native bees Confirmed Pollinator Link
Bee Confirmed Pollinator Link
Birds
Bird Confirmed Pollinator Link

Donate to CPC to Save this Species

Fall fundraising drive has begun! We're looking for 2,500 people to protect our planet. With you by our side, we will build a future where people live in harmony with nature. Come help and become a CPC donor today.

Donate Today