Purple nutsedge

Cyperus rotundus is a perennial plant, that may reach a height of up to 140 cm (55 in). The names "nut grass" and "nut sedge" – shared with the related species Cyperus esculentus – are derived from its tubers, that somewhat resemble nuts, although botanically they have nothing to do with nuts. As in other Cyperaceae, the leaves sprout in ranks of three from the base of the plant, around 5–20 cm (2–8 in) long. The flower stems have a triangular cross-section. The flower is bisexual and has three stamina and a three-stigma pistil, with the inflorescence having three to eight unequal spikes. The fruit is a three-angled achene. Young plants initially form white, fleshy rhizomes, up to 25 mm (1.0 in) in dimension, in chains. Some rhizomes grow upward in the soil, then form a bulb-like structure from which new shoots and roots grow, and from the new roots, new rhizomes grow. Other rhizomes grow horizontally or downward, and form dark reddish-brown tubers or chains of tubers.

Similar species. C. esculentus – is visually similar but has yellow to bright-yellow florets (lacking the darkened reddish colour of C. rotundus' inflorescence, which can be a bit greenish-pallid without), often arranged in a ladder-like way. C. longus – has leaves that sheath the stem and diverge from some way up the stem, and is invariably a rather larger plant. C. …

It prefers dry conditions, but will tolerate moist soils, and often grows in wastelands and in crop fields. The tubers are an important nutritional source of minerals and trace elements for migrating cranes.

C. rotundus has many beneficial uses. It is a staple carbohydrate in tropical regions for modern hunter-gatherers and is a famine food in some agrarian cultures.

Folk medicine. In traditional Chinese medicine, C. rotundus is considered the primary qi-regulating herb. The plant is mentioned in the ancient Indian ayurvedic medicine Charaka Samhita (circa 100 AD). Modern ayurvedic medicine uses the plant, known as musta or musta moola churna, for fevers, digestive system disorders, dysmenorrhea, and other maladies. Ayurvedic physicians use the plant for medicinal purposes in treating fevers, digestive system disorders, dysmenorrhea and other maladies. Modern alternative medicine recommends using the plant to treat nausea, fever and inflammation; for pain reduction; for muscle relaxation and for many other disorders. Arabs of the Levant traditionally use roasted tubers, while they are still hot, or hot ashes from burned tubers, for wounds, bruises, and carbuncles. Western and Islamic herbalists including Dioscorides, Galen, Serapion, Paulus Aegineta, Avicenna, Rhazes, and Charles Alston have described its use as a stomachic, emmenagogue, and deobstruent, and in emollient plasters. The antibacterial properties of the tubers may have helped prevent tooth decay in people who lived in Sudan 2000 years ago. …

C. rotundus was part of a set of starchy tuberous sedges that may have been eaten by Pliocene hominins. 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 BC to the Meroitic pre-Islamic Kingdom of 300–400 AD. 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 because of its ability to inhibit Streptococcus mutans. C. rotundus was employed in ancient Egypt, Mycenean 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.