pierre laszlo

Cyperus rotundus (Cyperaceae)

Plant of the month (©Pierre Laszlo, all rights reserved)
Cyperus rotundus (Cyperaceae).

In somewhat like manner to the tongue for Aesop, there being no greater good nor worse evil,  or to the French Revolution for Dickens, being the best of times and the worst of times, this is both a gift from the Gods and a scourge. Mankind has used this plant for millennia and yet it is now at a loss on how best to get rid of it. 
It has been used for food, with an antibacterial fringe benefit. But, as we shall see, the plant is also a pest, to farmers and gardeners.
But first what are we dealing with ? A sedge, it is in the same family as papyrus. A perennial, known as purple nutsedge, and originating in Eurasia, it reaches a height of 1.4 m (55 in). The leaves sprout in ranks of three from the base of the plant, around 5–20 cm long. The bisexual flowers show three-fold symmetry, with a triangular stem, three stamens and a three-stigma carpel. The fruit is likewise triangular in shape. 
Key to the story is the underground ramification : a young plant  develops a root system consisting in chains of white, fleshy rhizomes, each up to 25 mm across. These rhizomes later give rise to upwards-directed new shoots and roots, and to new rhizomes as well. Other rhizomes grow horizontally or downward, and form dark reddish-brown tubers or chains of tubers. 
In addition, the root system releases chemicals in the soil hostile to the growth of other plants. Purple nutsedge thus interfere with cultivation of, to cite a few, cilantro, cotton, bell pepper, tomato, radish, rice, and various other vegetables. 
In short, these rhizomes and tubers are a high-performance infestation device. The intensive network of underground tubers is incredibly resistant to most herbicides. Thus, Cyperus rotundus is known as "the world's worst weed," thriving in over 90 countries, including the USA, and infesting over 50 crops worldwide.
With such a dark underside, what could the good side be? It comes from the tubers as well. Even though they have a bitter taste, they are are rich in starch  and edible. Famine-stricken African populations have resorted to eating them. 
In the more distant past, hominids ate them during the Pliocene (5.333 million to 2.58 million years before the present). It continued being a staple for Aborigines in Central Australia. 
It was found also in human dental remains at the Al Khiday archaeological complex in central Sudan, dating from before 6700 BCE to the Meroitic pre-Islamic Kingdom of 300-400 CE. Moreover, the archeological evidence shows that Cyperus rotundus inhibited caries, by preventing growth of Spectrococcus mutans. Some among our forebears were aware of its dental care usefulness.