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Have you seen Long-thorn kiawe (Prosopis juliflora)?
Hawaii Early Detection Network Priority Pest for Kauai

Long-thorn kiawe thorns
Thorns can be up to 4 inches long.

Long-thorn kiawe can grow like a shrub or a tree with pale-yellow cylinder shaped flower spikes and yellowish-brown seeds pods.
Long-thorn kiawe plant
Long-thorn kiawe leaves are larger than common kiawe.
Images: Forest & Kim Starr

Identification: Long-thorn kiawe can grow as a rambling shrub or tree ranging from 6' to 30' tall. The thorns are up to 4" long. It's pale yellow flowers are numerous and grow in cylinder-shaped spikes up to 4" long. Mature seed pods are flat, curved, yellowish brown and 3-8 inches long.
Impacts: The long-thorn kiawe thorns are able to pierce entirely through rubber slippers, boots, and car/truck tires. These thorns also have poison-tipped ends that can cause bruises and swelling. The long-thorn kiawe grows in dense thickets that crowd out native costal plants. It is capable of rendering large areas impassible, preventing beach access.
Dispersal Mechanism: Longthorn kiawe produces thousands of seeds per year, which are carried long distances by water. The trees easily resprout after damage.
Origin, Distribution, and Habitat: Long-thorn kiawe is native to Africa and was first noted in Hawai'i in 1978. The introduction history is unknown but it was possibly introduced for agriculture or accidentally. The current, known distribution of this pest is on Kaua'i, O'ahu, and Moloka'i. On Kaua'i, long-thorn kiawe invades beaches of Maha'ulepu, Mana, the Pacific Missle Range Facility, Waimea, and Kekaha. The preferred habitat is costal and dry. This plant can withstand drought and is somewhat tolerant of saltwater. Please report any new sightings of this pest!

More information about this pest external link

Long-thorn kiawe look-alikes:

Bidens pilosa

Common kiawe has yellow to white flowers and smaller thorns than long-thorn kiawe.

Common kiawe (Prosopis pallida):
Common kiawe is common invasive plant throughout Hawai'i and can be confused with the long-thorn kiawe. Common kiawe always grows into an upright tree, unlike the rambling growth-form of long-thorn kiawe shrubs or trees. Common kiawe can also be distinguished by its absent thorns or smaller 1" thorns compared to the large 3"-4" thorns of the long-thorn kiawe.

Bidens pilosa
Last Updated: Monday January 30 2012. If you have any questions about the Hawaii Early Detection Network contact
Funding and support for this project was made possible by the Hawai'i Invasive Species Council, the USDA Forest Service State and Private Forestry assistance, and University of Hawai'i-Pacific Cooperative Studies Unit.