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Description: Cyperus rotundus is a perennial, tufted, erect sedge, 10 to 50 cm (4-20 in) tall which produces hard, scaly, brown-black tubers borne on underground runners or rhizomes. Its leaves, are 5 to 15 cm (2.5-6 in) long, narrow, grass-like and folded along the midrib. The inflorescence is reddish-brown flower spikelets, 1 to 2 cm (1/2-1 in) long with 2 to 4 leaf-like bracts 1 to 12 cm (½-4½ in) long, borne on unequal rays up to 6 cm (2½ in) long formed in loose terminal umbels produced at the top of three-angled flowering culms (stems). Its oblong, 3-sided achene fruits are small and brown. Key characteristics for C. rotundus include “3-ranked leaves, triangular culm, [and] flattened spikelets with exserted styles” (see http://www.botany.hawaii.edu/faculty/carr/cyper.htm; Thaman et al. 1994). The common English names of “nut grass” and “nut sedge,” which are used in reference to C. rotundus, are shared with the related species Cyperus esculentus L.; these names are derived from appearance of the “tubers” of these species that somewhat resemble nuts, although botanically they are not true nuts.
Distribution: The Cyperus rotundus sedge has been identified by some as “the world's worst weed” occurring as an alien species in about 100 countries (e.g., see Holms et al. 1997; Sivapalan 2013). Possibly native to India, this purplish “nut sedge” is reportedly widespread from the warm temperate to the tropical zones of southern Europe, Africa, Asia, Australia, the Pacific and the Americas. C. rotundus grows in many types of soils, especially in drier areas, and can tolerate relatively high temperatures producing an extensive system of underground tubers from which new stems can regenerate. Itis very difficult to control once it is established, and is said to smother, more or less, all other surrounding plants while also removing large quantities of moisture and nutrients. As a cosmopolitan, weedy sedge, C. rotundus occurs in farmlands, grasslands, and sandy or gravelly shores, riverbanks, and waste places. While it is a major weed of cultivated crops and of gardens, it is only a minor weed in other environments and does not grow well in shady areas. On the other hand, tt should be noted that C. rotundus has a widespread, long-lasting record of ethnobotanical use for food, medicine and craft making (e.g., see Simpson and Inglis 2001).
Uses by Islands or Island Groups: Although this common sedge is a potentially invasive weed in many wet areas, it seems to have a very ancient ethnobotanical relationship with humans. C. rotundus is reputedly a key carbohydrate source in some tropical regions for recent hunter-gatherers, and is said remain as a famine food in some agrarian cultures. It also “has many useful medicinal and aromatic qualities, though today it is considered to be the world’s most costly weed” (Buckley et al. 2014). In sum, this invasive species of modern times also has a very ancient history of human use as a food and purifying agent:
“C. rotundus was part of a set of starchy tuberous sedges that may have been eaten by Pliocene hominins. It was a staple of Aboriginal populations in Central Australia. Biomarkers and microscopic evidence of C. rotundus are present in human dental calculus found at the Al Khiday archaeological complex in central Sudan dating from before 6700 BCE to the Meroitic pre-Islamic Kingdom of 300-400 CE. It is suggested that C. rotundus consumption may have contributed to the relatively low frequency of dental caries among the Meroitic population of Al Khiday due to its ability to inhibit Streptococcus mutans. C. rotundus was employed in ancient Egypt, Mycenaean Greece, and elsewhere as an aromatic and to purify water. It was used by ancient Greek physicians Theophrastus, Pliny the Elder, and Dioscorides as both medicine and perfume” (Buckley et al. 2014).
In recent times, compounds extracted from purple C. rotundus have been shown to have medicinal properties such as the “reduction of fever, inflammation, and pain,” and a review of “the literature contains numerous references to the use of this plant’s roots for essential oils and its seeds for food products” (see http://plants.usda.gov/plantguide/). For example, C. rotundus has a wide range of medicinal and pharmacological applications in South Asia: According to the Indian Ayurveda medical tradition, “C. rotundus rhizomes are considered astringent, diaphoretic, diuretic, analgesic, antispasmodic, aromatic, carminative, antitussive, emmenagogue, litholytic, sedative, stimulant, stomachic, vermifuge, tonic and antibacterial” (Sivapalan 2013, also see http://tropical.theferns.info/viewtropical.php?id=Cyperus+rotundus).
Uses in the Mariana Islands:More than a hundred years ago, Safford (1905: 254) indicated that C. rotundus was quite “common in Guam, often growing in the yards of Agaña with grasses and near the shore” … and referred to as “a most troublesome weed in garden patches.” On the other hand, McMakin (1978:46), referred to this common sedge as a source of traditional Chamorro medicine: “An indigenous common garden herb that is used in the treatment of ulcers.” The local Chamorro names Chaguan Umatag or Humátag for this nutgrass (C. rotundus) on Guam, may be derived from the Japanese name for this plant“Hamasage”:
“A sedge growing in sandy places, with aromatic tuberous rootstock., having the odor and taste of camphor. Very common in Guam, often growing in the yards of Agaña with grasses and near the shore. It is a most troublesome weed in garden patches. In Japan, its roots are collected in the winter, dried, and used for medicine.” (http://guamology.com/cyperus-rotundus.html).
Uses in the Marshall Islands: In these limestone atolls and reef islands, C. rotundus is apparently a relatively recent introduced weed (in the 20th century, possibly by the Japanese?) It is now reportedly common in gardens, especially at the Laura Experimental Farm on Majuro, as well as “in other vegetable farms at Laura and along roadsides, other ruderal sites and in sandy areas” (Vander Velde 2003:38). C. rotundus could become a wide spread invasive species on Majuro and other Marshall Island atolls; however, Okabe (1941d:14) listed the “root” of the C. rotundus sedge as a food source on Jaluit Atoll in the Marshall Islands.
Uses on Nauru: C. rotundus may have been a pre-World War II introduction on Nauru where it is common and found in many environments, especially as an extensive weed in lawns and gardens, as well as “in swamps in Meneng” (Thaman et al. 1994:51).