Kohekohe is a small, indigenous rush that is equally at home in higher, cooler elevations as it is in lower, warmer sites. A wild Eleocharis obtusa in a wetland in Huntington, Indiana (Photograph courtesy of Paul Rothrock CC BY-NC 4.0). 

Growth Requirements

General

    Kohekohe plants thrive in very wet environments, making them ideal to grow in pots without drainage holes, ponds, or aquariums with its roots fully submerged in water. In your landscape or home water features, you may want to use a method to control mosquitoes, fungus gnats and black flies such as Mosquito Dunks® or Mosquito Bits®. These are natural products that contain Bacillus thuringiensis israelensis (Bti), a target-specific microbial larvicide, which means it controls only the larval stage of development utilizing a bacterial active ingredient. When Bti is placed in water, the dunks or bits float and release the natural soil-borne bacterium. This bacterium is ingested by the mosquito larvae, and the other aforementioned insects, within the water and soon after kills the larvae with no effect on anything else.

    The clumping nature of kohekohe makes them easy to manage, and they can easily be grown from seeds, but require consistent moisture for germination. Like most rushes, kohekohe prefers full sun and benefits from occasional applications of organic fertilizers. However, it is important not to over-fertilize in ponds, aquariums, or similar water features, as this can lead to excessive algae growth.

    For a dense covering, plants should be spaced 6 to 8 inches apart. If you want to showcase the charm of this little rush, space them one foot apart.

Pests and Diseases

    Flocks of small seed-eating passerine birds (munias, waxbills, silverbills) regularly visit this rush but do not seem to adversely affect the plant's larger mature clumps. Sometimes, smaller clumps or immature plants, though, are often bent over or even broken from alighting feeding birds. They could be considered pests if you have few plants; otherwise, they pose no threat.

Special Features and Information

General

    The Sedge family, also known as Cyperaceae, is home to over 120 species of spikerushes, which are predominantly water-loving plants, although some can be found in mesic environments. In the Hawaiian Islands, there are two native species of spikerushes and at least four naturalized species.

    One of the most well-known spikerushes is the Chinese water chestnut or water chestnut (Eleocharis dulcis), known for its tubers on the rhizomes that can be cooked or eaten raw. The Chinese name is mā tí ("horse hoof") due to the corm, resembling a horse's hoof. In Fiji and Niuafoʻou in Tonga, this species is referred to as kuta, and the stems are woven into soft sleeping mats. In Samoa, where it is called ʻutuʻutu, it may have been used to some extent in the past [Whistler 2009].

    Kohekohe (Eleocharis obtusa) is among the few native rushes. It has a robust variety known as E. obtusa var. gigantea that has larger floral characteristics but is considered rare.

Is it a Rush or a Sedge? 

    While rushes and sedges both belong to the same family (Cyperaceae), there is a straightforward method to differentiate between the two. Rushes are characterized by round, cylindrical stems or leaves, which may be hollow like a drinking straw when cut open. On the other hand, sedges are identified by triangular, often sharp-edged leaves that can cut you. To simplify the distinction, remember that "rushes are round, while sedges have edges."

Hawaiian Name

    The origin of the Hawaiian name, kohekohe, is currently unknown. However, according to Te Māra Reo--The Language Garden, it is believed to have originated from the Proto South Central Pacific word "Kofe," which refers to bamboo, specifically Schizostachyum glaucifolium (Poaceae), and "Kofekofe" to describe plants with bamboo-like qualities [Te Māra Reo].

    Interestingly, the Hawaiian name ʻohe is used for the Polynesian introduced bamboo (Schizostachyum glaucifolium), as well as a few other native plants, such as Isachne distichophylla and Joinvillea ascendens, which are all tall and straight like kohekohe (E. obtusa).

Etymology

    The genus name Eleocharis comes from the Greek word helos, meaning "of the marsh or meadow," and charis, which means "grace, favor, or loveliness" [Gledhill 2008]. The specific Latin epithet, obtusa, is in reference to the blunt seed head of this species [Gledhill 2008].