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Useful Tropical Plants

Acacia koa

A.Gray

Fabaceae


Classification of the genus Acacia (in the wider sense) has been subject to considerable debate. It is generally agreed that there are valid reasons for breaking it up into several distinct genera, but there has been disagreement over the way this should be done. As of 2017, it is widely (but not completely) accepted that the section that includes the majority of the Australian species (including this one) should retain the name Acacia, whilst other sections of the genus should be transferred to the genera Acaciella, Mariosousa, Senegalia and Vachellia[
K
Title
Plants for a Future
Author
Ken Fern
Description
Notes from observations, tasting etc at Plants For A Future and on field trips.
].

+ Synonyms

Acacia hawaiiensis (Rock.) O.Deg. & I.Deg.

Acacia kauaiensis Hillebr.

Racosperma koa (A.Gray) Pedley.

Common Name: Koa Acacia

Acacia koa
Trunk of an old tree
Photograph by: Forest and Kim Starr
Creative Commons License
Acacia koa Acacia koa Acacia koa Acacia koa Acacia koa Acacia koa Acacia koa

General Information

Koa acacia is an evergreen tree that usually grows about 20 metres tall, though it sometimes reaches up to 35 metres. Some populations are smaller and more shrub-like[
338
Title
IUCN Red List of Threatened Species
Publication
 
Author
 
Website
http://www.iucnredlist.org/
Publisher
 
Year
0
ISBN
 
Description
A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
].
This species (as of 2006) provides one of the most expensive timbers in the world, used mainly for furniture, veneer and crafts[
338
Title
IUCN Red List of Threatened Species
Publication
 
Author
 
Website
http://www.iucnredlist.org/
Publisher
 
Year
0
ISBN
 
Description
A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
]. The only Acacia that is native and endemic to Hawaii, plantations have been established there in order to provide native vegetative cover on degraded sites[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].
Acacia koa is currently known to be the dominant canopy endemic tree occurring on six of the Hawaiian islands. The species occurs in mesic forest in a wide range of habitats and elevations. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2013)[
338
Title
IUCN Red List of Threatened Species
Publication
 
Author
 
Website
http://www.iucnredlist.org/
Publisher
 
Year
0
ISBN
 
Description
A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
].

Known Hazards

Especially in times of drought, many Acacia species can concentrate high levels of the toxin Hydrogen cyanide in their foliage, making them dangerous for herbivores to eat.

Botanical References

200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.

Range

Pacific Islands - Hawaii.

Habitat

Both pure and mixed forest stands, usually with native ohia (Metrosideros polymorpha). Also a co-dominant in several other major forest types including Koa/Mamane (Sophora chrysophylla) Montane Dry Forest and Koa/Ohia/A'e (Sapindus soponaria) Forest[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].

Properties

Conservation StatusLeast Concern
Other Uses Rating *  *  *
HabitEvergreen Tree
Height20.00 m
Growth RateFast
PollinatorsBees
Self-fertileYes
Cultivation StatusCultivated, Wild

Cultivation Details

Trees grow naturally in the tropics, usually at an elevation between 180 - 6,000 metres[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
]. They grow in areas where the mean annual rainfall is in the range 1,900 - 5,100mm[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].
It grows well in moderately to well-drained, medium to very strongly acid soils on both flatland and steep slopes[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
,
338
Title
IUCN Red List of Threatened Species
Publication
 
Author
 
Website
http://www.iucnredlist.org/
Publisher
 
Year
0
ISBN
 
Description
A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
]
Trees occurring in dense, wet native forest stands typically retain a straight, narrow form[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
]. In the open, trees develop more spreading, branching crowns and shorter, broader trunks[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
]. The tree has one main tap root and an otherwise shallow, spreading root system[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].
Observations suggest Acacia koa can flower almost any time of year, depending upon local weather conditions. Trees appear to be self-fertilizing[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
]. Pods reach maturity at 4-6 months, depending on location and weather conditions[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
]. Seed production begins when trees are 5 years old[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
]. A. koa bears seed often and abundantly[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].
A fast-growing tree[
338
Title
IUCN Red List of Threatened Species
Publication
 
Author
 
Website
http://www.iucnredlist.org/
Publisher
 
Year
0
ISBN
 
Description
A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
]. On favourable sites, planted seedlings grow to 9 metres in 5 years[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
]. A. koa is nodulated by the slow-growing Bradyrhizobium spp. Common in tropical soils. It nodulates heavily in a variety of soils, suggesting it is effective with a wide variety of Bradyrhizobia strains[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].

Edible Uses

None known

Medicinal

The bark of all Acacia species contains greater or lesser quantities of tannins and are astringent. Astringents are often used medicinally - taken internally, for example. they are used in the treatment of diarrhoea and dysentery, and can also be helpful in cases of internal bleeding. Applied externally, often as a wash, they are used to treat wounds and other skin problems, haemorrhoids, perspiring feet, some eye problems, as a mouth wash etc[
601
Title
The Useful Native Plants of Australia.
Publication
 
Author
Maiden J.H.
Website
http://www.biodiversitylibrary.org
Publisher
Turner & Co.; London.
Year
1889
ISBN
 
Description
Terse details of the uses of many Australian plants and other species naturalised, or at least growing, in Australia. It can be downloaded from the Internet.
,
K
Title
Plants for a Future
Author
Ken Fern
Description
Notes from observations, tasting etc at Plants For A Future and on field trips.
].
Many Acacia trees also yield greater or lesser quantities of a gum from the trunk and stems. This is sometimes taken internally in the treatment of diarrhoea and haemorrhoids[
601
Title
The Useful Native Plants of Australia.
Publication
 
Author
Maiden J.H.
Website
http://www.biodiversitylibrary.org
Publisher
Turner & Co.; London.
Year
1889
ISBN
 
Description
Terse details of the uses of many Australian plants and other species naturalised, or at least growing, in Australia. It can be downloaded from the Internet.
].

Agroforestry Uses:

Most plantations in Hawaii have been established to provide vegetative cover on sites degraded by decades of intense grazing[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].

Other Uses

The wood is hard. It is used by local people to make spears, paddles etc[
46
Title
Dictionary of Economic Plants.
Publication
 
Author
Uphof. J. C. Th.
Publisher
Weinheim
Year
1959
ISBN
-
Description
An excellent and very comprehensive guide but it only gives very short descriptions of the uses without any details of how to utilize the plants. Not for the casual reader.
].
The heartwood is highly valued for its unique grain, varied colour and workability. It seasons well without serious warping or splitting. Curly-grained wood, the result of both stress and genetics, is preferred over straight-grained wood[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
]. Wood colour ranges from a subtle yellow to a striking dark red-purple. The specific gravity of wood averages 0.40, but with curly-grained wood can be as high as 0.65. It is the premier Hawaiian timber for furniture, cabinetry, interior work and woodcrafts[
303
Title
World Agroforesty Centre
Publication
 
Author
 
Website
http://www.worldagroforestry.org/
Publisher
 
Year
0
ISBN
 
Description
An excellent online database of a huge range of trees giving very good information on each plant - its uses, ecology, identity, propagation, pests etc.
].

Propagation

The seed of most, if not all, members of this genus has a hard seedcoat and may benefit from scarification before sowing to speed up germination. This can usually be done by pouring a small amount of nearly boiling water on the seeds (being careful not to cook them!) and then soaking them for 12 - 24 hours in warm water. By this time they should have imbibed moisture and swollen - if they have not, then carefully make a nick in the seedcoat (being careful not to damage the embryo) and soak for a further 12 hours before sowing. Once treated, seeds are sown in nursery beds. 1 week after germination, seedlings are transplanted into nursery tubes or bags. Seedlings are ready for transplanting into the field when they are approximately 20cm tall, (after 3-4 months in the nursery). Establishment by direct seeding or encouragement of natural regeneration is recommended as heart rot occurs during transplanting. One study recommends air-layering as the best vegetative propagation technique.

The seeds are durable and easy to store. They germinate after many years of storage if kept in a cool, dry place. The most effective method for improving seed germination is mechanical scarification. However, hot water soaking works well and is a more practical method, seed should be soaked in boiled water for 24 hours. Seeds are seldom dispersed far from the tree and remain viable in the soil for up to 25 years.
Cite as: Tropical Plants Database, Ken Fern. tropical.theferns.info. 2018-09-26. <tropical.theferns.info/viewtropical.php?id=Acacia+koa>

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