Tribulus cistoides has spiky fruits that turn from green to tan as they ripen; unfortunately, local surfers and many beachgoers are said to despise this native plant. A flowering wild nohu on Midway Atoll. (Fruits and wild plant photographs courtesy of Forest & Kim Starr CC BY 3.0). Inland cultivated nohu.

Growth Requirements

General

    Tribulus cistoides is a controversial plant because of its spiny fruits. As a groundcover, with its silvery leaves and large sulfur-yellow flowers, it is beautiful and does an okay job of weed control. However, if you have children, or pets, or like to walk barefoot (or even with slippahs) in your yard, nohu might not be the right plant for you — its spiny fruits are merciless!

    Nohu does best in areas with full sunlight for all or most of the day but can also tolerate partial shading. It requires little to no watering once established, and too much water will cause it to lose much of its silvery appearance. Nohu grows best in sandy soils but will also grow in coralline, lava/cinder, clay, and organic-dominant soils provided the soil drains well. It is tolerant of extreme heat, drought, strong winds, and salt spray. 

    Under optimum conditions, nohu grows and flowers quickly once established in the ground. Since it is short-lived, you should regularly collect and propagate its seeds so you have replacement plants when needed; nohu can also be propagated by rooting cuttings [Ramírez et al. 2014].

Pests and Diseases

    Nohu is infrequently attacked by sap-sucking pests such as aphids, mealybugs, spider mites, and thrips, which are often farmed and protected by ants. Refer to the Pests & Diseases page for treatments to eliminate or control these pests.  

Special Features and Information

General

    Tribulus cistoides is the sole native Hawaiian member of Zygophyllaceae, a family with around 285 species in 22 genera worldwide with many species growing in dry habitats [WikipediA; Zygophyllaceae]. 

    In many places, including Hawai‘i, Tribulus cistoides is considered an injurious weed because its spiny fruits can be quite painful when stepped on with bare feet. (The spines will even go through rubber slippers.) Therefore, nohu has been eradicated from many beaches and other populated coastal areas in Hawai‘i (and elsewhere). In contrast, nohu has been planted, and its reproduction encouraged in the Northwestern Hawaiian Islands to improve native bird habitat.

    Morin & Conant [1998] have reviewed the evidence that nohu was/is an important plant for native birds on Laysan Island (Kauō). Here are some of their findings: Schauinsland [1899] noted that, in 1896, nohu occurred "almost everywhere on the island, especially in sandy areas between the single Eragrostis bunches." This quote suggests that nohu was more common on Laysan in the 1800s than it is currently. It was also one of the few plants to survive the island's devegetation by rabbits (1903-23). During the devegetation, the Laysan Finch (Telespiza cantans) population also declined. The Finch is an omnivore that feeds on many plants, including nohu, eating its seeds, leaves, flowers, runners, and seedlings. It has been reported that the Laysan Duck forages under nohu (probably for invertebrates) and that the extinct Laysan Honeycreeper fed on the nectar of nohu flowers [Munro 1960].

Hawaiian Name

    Nohu is also the Hawaiian name for scorpionfish (Scorpaenopsis spp.), about 25 species with poisonous spines [Pukui & Elbert 1986]. While nohu (the plant) fruits do have spines, they are not poisonous.

Etymology

    Tribulus is the Latinized version of the Greek word for a caltrop, tribolos [Wagner et al. 1990]. A caltrop is a 4-pointed weapon such that one point is always pointing upwards. It was/is used to cripple troops, horses, etc., during wartime. The species name, cistoides, comes from the genus name Cistus (from the Greek kistos) and the Greek suffix -oides, which means "resembling," implying a resemblance (of the flowers) between nohu and members of the genus Cistus, also known as rockrose [Flora of Australia;Tribulus cistoides].