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Acacia koa
Alternative Botanical Names
Acacia hawaiiensis
Acacia heterophylla
Acacia kauaiensis
Acacia koaia
Racosperma kauaiense
Racosperma koa

Common Names
Potential or Traditional Uses
Photo of Acacia koa flowers and leaves
Acacia koa is a large tree becoming 50 feet tall in cultivation, but very old trees can become much taller. At maturity, the trees are 10 to 25 feet in diameter. The "leaves" are not true leaves; they are modified leaf stems, or phyllodes, which function as leaves. These crescent-shaped phyllodes are gray-green and range from 3 to 9 1/2 inches in length.

The small, yellow, powder-puff shaped flowers occur in clusters either at the ends of the branches or at the bases of the phyllodes. There are three forms of Acacia koa which are sometimes considered subspecies. One of these, subspecies koaia, is shorter with a more gnarled appearance and is commonly considered horticulturally distinct. (Bornhorst 1996; Wagner 1990)

Habitat and Geographic Range
Acacia koa is endemic to Hawai'i and is found on all the main islands except Kaho'olawe and Ni'ihau. It is often a dominant plant in dry to wet forests at elevations ranging from 200 to 6,500 feet. (Wagner 1990)
Propagation by Seeds
The seeds of Acacia koa are contained in brown bean pods 1/4 to 1 inch wide and up to 12 inches long. The oval seeds are less than 1/2 inch long. Beetles often feed on the seeds. These seeds will have holes in them, but sometimes the seed is intact enough to germinate in spite of this damage. The seeds need to be removed from the dried pods by hand. There are generally at least 5 or 6 seeds in each pod.

Yoshinaga (1998a) suggests using boiling water to speed germination of Acacia koa seeds. Use 3 or 4 times the amount of boiling water as you have seeds and let the seeds soak overnight. The seeds could be damaged if you use too much boiling water. After this treatment, the seeds will start germinating in about 2 weeks. Either damp potting medium or damp paper towels can be used for germination. Bornhorst also suggests that the seeds be soaked for 24 hours in water that was "initially almost boiling."

NTBG recommends that the seeds be scarified, i.e. the seed coat should be penetrated. This can be done using sandpaper, nail clippers, or by cracking with a hammer. Care must be taken to avoid damaging the inner part of the seed. Lilleeng-Rosenberger reports germination rates for scarified seeds ranging from 65% to 80%. In his germination studies, Obata found that untreated seeds of Acacia koa had germination rates of less than 5%.

After scarification, the seeds should be soaked in water for 24 hours. The seeds should be planted in soil-less potting mix at a depth of about twice the diameter of the seed. Acacia koa seeds generally take 11 to 24 days to germinate; however, Lilleeng-Rosenberger reports some scarified seeds germinating in as few as 7 days.

Acacia koa seeds store well. Yoshinaga (1998b) states that they appear to keep well for years at room temperature and humidity. Storing them at lower temperatures and humidity would probably increase the length of time the seeds remain viable. (Bornhorst 1996; Lilleeng-Rosenberger 1996; NTBG 1996; Obata 1967; Yoshinaga 1998a; Yoshinaga 1998b)

Propagation by Cuttings
No information located to date.
Propagation by Division
Not applicable.
Propagation by Air Layers
No information located to date.
Propagation by Grafting
No information located to date.
Propagation by Tissue Culture
No information located to date.
Bornhorst, Heidi L. 1990. Introduction to xerophytic native Hawaiian plants. The Bulletin of the National Tropical Botanical Garden 20 (3):49-54.

Bornhorst, Heidi L. 1996. Growing native Hawaiian plants: a how-to guide for the gardener. Honolulu: The Bess Press. p. 59-61.

Lilleeng-Rosenberger, Kerin. 1996. Plant propagation notebook. Unpublished materials: National Tropical Botanical Garden.

National Tropical Botanical Garden (NTBG). 1996. Ten native Hawaiian trees for urban landscapes. Lawai, Hawaii: Education and Plant Science Departments. National Tropical Botanical Garden.

Obata, John K. 1967. Seed germination in native Hawaiian plants. Newsletter of the Hawaiian Botanical Society 6 (3):13-20.

Wagner, Warren L., Darrel R. Herbst, and S. H. Sohmer. 1990. Manual of the flowering plants of Hawai'i. 2 vols., Bishop Museum Special Publication 83. Honolulu: University of Hawaii Press and Bishop Museum Press. p. 641-642.

Yoshinaga, Alvin. 1998a. Growing native. Newsletter of the Hawaiian Botanical Society 37 (1):6-7.

Yoshinaga, Alvin. 1998b. Storing seeds of some native rain forest plants: some simple methods. Newsletter of the Hawaiian Botanical Society 37 (2):28-32.

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The image in this record is used with permission from Dr. Gerald Carr's Web site "Hawaiian Native Plants" at

Last updated:
16 February 2002

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