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prickly seed weed hawaii

Hawai‘i-Pacific Weed Risk Assessment Score : 19, High Risk.

Regulatory Status : Hawaii Noxious Weed (HAR 68)


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.

Prevention and Control Category : KISC Target Species

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.

Java plum trees spread naturally on most of the islands.

Golden Shower Tree

The Macadamia Nut tree, bearing the tasty nut with same name is native to Australia but was found to grow well in the Hawaiian climate. The nuts are commercially grown on the Big Island, and the tree is occasionally seen scattered as a dooryard tree on the other islands.



Leaves: Leaves can be up to 8 inches long, and are silvery-green with white veins and deep regular lobes. The upper surface of the leaf is smooth, while the underside has a few prickles along the midrib. The edges of the leaf are often lined with many prickles.

Mexican prickly poppy is poisonous to livestock, but is not readily eaten, so there are relatively few cases of poisoning from this plant. However, plants in hay have caused poisoning. Seeds are its most toxic part, but the entire plant contains toxic elements.

Key Characteristics

Flowers: Flowers are yellow and approximately 2.5 inches in diameter.

Seed: Seeds are produced inside a prickly capsule measuring about 1.5 inches in length. Approximately 3 to 6 openings in the capsule allow the seeds to disperse, but many seeds can remain inside the capsule for weeks until wind or animals shake the plant. Up to 400 seeds can be enclosed by a single capsule and they may stay dormant in the soil for many years.

Although this weed is common throughout Florida, it is typically not a wide-spread problem. For those who wish to control it, 2,4-D, WeedMaster (or other products containing 2,4-D + dicamba), or GrazonNext HL are the most effective and economical herbicides for control. The application rate for 2,4-D or WeedMaster is 3 pt/acre for broadcast applications, and 24 oz/acre for GrazonNext HL If spot spraying is necessary, a 3% solution of either 2,4-D or 2,4-D + dicamba or a 1% solution of GrazonNext HL in water is appropriate. Remember, it is best to treat a younger plant, especially before seed set occurs, to ensure that seeds are not added to the soil seedbank.