Hawaiian Names with Diacritics
- Oahu riverhemp 
- Sesbania arborea
- Sesbania hawaiiensis
- Sesbania hobdyi
- Sesbania molokaiensis
- Sesbania tomentosa f. arborea
Names with Unknown Sources
- Tree ohai
Endangered Species Status
Plant Form / Growth Habit
- Partially Woody / Shrub-like
- Sprawling Shrub
Mature Size, Height (in feet)
- Shrub, Dwarf, Less than 2
- Shrub, Small, 2 to 6
- Shrub, Medium, 6 to 10
- Shrub, Tall, Greater than 10
- Tree, Small, 15 to 30
Mature Size, Width
ʻOhai can have a 15- to 45-foot spread. The prostrate varieties have the greatest spread.
Long lived (Greater than 5 years)
- Ground Cover
- Specimen Plant
Additional Landscape Use Information
These endangered shrubs prefer sunny, dry growing conditions and generally tolerant of wind. ʻOhai offers a different leaf texture to the landscape. The prostrate forms can be used as groundcovers, shrub forms as accent or hedges, and tree forms as accent, tall hedge or screen plants.
Tree or tall bush forms with top heavy growth may need to be staked to prevent toppling over due to the wind, especially if grown in softer (i.e. loamy, sandy) soils. Too much water and fertilizer (especially with extra nitrogen) may be the culprits for this luxuriant growth and few flowers. [David Eickhoff, Native Plants Hawaiʻi]
These shrubs do well in pots with excellent or perfect drainage and with full sun. Allow potting mix to dry between waterings. Black sooty mold on trunk, twigs and leaves are indications of excessive watering. This needs to be corrected or it will likely lead to pests (e.g. root mealybugs, nematodes) and root rot. If you are one that cannot keep your hands off the water hose, this may not be a good plant for you.
Because ʻohai are nitrogen-fixing plants, they will not only provide a natural source of nitrogen for themselves but will enrich the soil with nitrogen benefiting other plants growing around them as well.
Source of Fragrance
Additional Fragrance Information
On sunny days the leaf clusters at the stem tips have a fragrance that resembles the scent of nectarines. The Kaʻena Point form have the strongest smell. [Rick Barboza, Hui Kū Maoli Ola]
Plant Produces Flowers
- Light Orange
Additional Flower Color Information
The flowers are an inch or so long and extremely variable in color, size and shape. Depending on the original location,ʻohai flowers can be found in colors from light to dark red, subtle to bright orange, apricot, and clear yellow. The centers of the flowers are usually yellow or greenish yellow.
- Year Round
Additional Blooming Period and Fruiting Information
ʻOhai bloom sporadically throughout the year, with peak blooming periods in winter and spring after it rains in their natural environment (e.g. Kaʻena Pt., Oʻahu).  The unscented flowers have a sweet nectar. [Rick Barboza, Hui Kū Maoli Ola]
Long greenish bean pods follow flowering. The pods will turn light brown and woody when ripe, with several squarish-shaped long, dark to olive green beans inside.
Additional Plant Texture Information
ʻOhai leaf textures range from pubescent to glabrous (without hairs). The leaf size varies among varieties.
- Dark Green
- Gray / Silverish
- Medium Green
Additional Leaf Color Information
ʻOhai leaf color ranges from silvery to dark green.
Additional Pest & Disease Information
Plants are subject to attacks by black stink bugs, black twig borers, spider mites, aphids, scale, and root knot nematodes.
Foliar feeding in early morning with a water-soluble or an organic fertilizer (e.g. kelp or fish emulsion) at one third to one fourth the recommended strength monthly has proved beneficial. However, since ʻohai are nitrogen-fixing plants they requirenfertilizers with little or no supplemental nitrogen. [David Eickhoff, Native Plants Hawaiʻi]
Additional Water Information
ʻOhai does not like "wet feet," that is, constant moisture at the roots and will soon become host to a number of pests and fungal diseases as a result of excess watering. Do not over water these xeric plants!
Soil must be well drained
- Full sun
- Partial sun
Additional Lighting Information
ʻOhai has been observed growing in partial shade in cultivation, but growth appears uncharacteristic and weak with few or no flowers. Best to grow these xeric shrubs or small trees in full sun. [David Eickhoff, Native Plants Hawaiʻi]
Spacing is really dependant on the form being used, but perhaps no less than the minimal width of 15 feet.
- Salt Spray
While seashore forms or varieties are salt tolerant, it is not known if upland or arboreal varieties have this tolerance.
- Northwest Islands
Natural Zones (Elevation in feet, Rainfall in inches)
- Less than 150, 0 to 50 (Dry)
- 150 to 1000, 0 to 50 (Dry)
- 1000 to 1999, 0 to 50 (Dry)
- 2000 to 2999, 0 to 50 (Dry)
Additional Habitat Information
ʻOhai are naturally found on sandy beaches, dunes, soil pockets on lava, and along pond margins (only Mānā, Kauaʻi). Formerly widespread, ʻohai is now extinct on Niʻihau and rare and restricted to relict populations elsewhere in the main islands. In the Northwest Islands ʻohai is found on Necker (Mokumanamana) and is a rather common component in the shrubland on Nīhoa (Moku Manu).
ʻOhai (Sesbania tomentosa) is an endemic member of the Pea family (Fabaceae).
ʻOhai is also the name for the non-native monkeypod or rain tree (Samanea saman), and the white monkeypod (Albizia lebbecki). The name is also used in part for other plants such as, the large white edible flowers of ʻohai keʻokeʻo or katuray (Sesbania grandiflora), and the red-flowered form ʻohai ʻulaʻula (S. grandiflora var. coccinea); ʻohai ʻula or royal poinciana (Delonix reginia); and ʻohai aliʻi or Pride of Barbados (Caesalpinia pulcherrima).
The generic name Sesbania is derived from sesban, the Arabic name for Sesbania sesban (syn S. aegyptiaca), Egyptian rattlepod.
The specific epithet tomentosa means "furry" or literally "covered with matted hairs," though not all forms are furry.
The common name Oʻahu riverhemp is admittedly an unusual and odd common name for this species, but one that others outside Hawaii nei may recognize. 
Some reference sources spell the Hawaiian name of Sesbania tomentosa with the macron kahakō over the "o" as ʻōhai; others do not. The Native Plants Hawaiʻi knowledgebase chooses to follow Pukui & Elbert's spelling with no kahakō as ʻohai. 
An arborescent, or tree, form is found in central Molokaʻi and is the woodiest of the numerous forms of ʻohai growing to 20 feet tall. 
There has been mild controversy about how long ʻohai live. Some put it at an estimate of 5 to 7 years or less; others have cultivated plants in excess of these years. ʻOhai at Kaʻena Point, Oʻahu, for example have been inexistence for well over a decade. [David Eickhoff, Native Plants Hawaiʻi]
Early Hawaiian Use
ʻOhai were one of the favored lei flowers by early Hawaiians. 
Early Hawaiians on Niʻihau called this plant ʻohai o Papiahuli, the meaning is unknown. 
ʻOhai are still used today in lei and strung much like other native pea-like flowers, such as ʻāwikiwiki, māmane, nanea, nuku ʻiʻiwi, and wiliwili. 
 "Recovery Plans for Multi-Island Plants" by USFWS, pages 140, 143, 145.
 "A Chronicle and Flora of Niihau" by Juliet Rice Wichman and Harold St. John, page 100.
 http://www.wehewehe.org [accessed 9/9/09]
 "Hawaiian Dictionary" by Mary Kawena Pukui & Samuel H. Elbert, page 276.
 "Nā Lei Makamae--The Treasured Lei" by Marie A. McDonald & Paul R. Weissich, pages 108-109.
 http://www.biolib.cz/en/taxon/id209244/ [Accessed 8/22/10]
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