Tiger Nuts: Cultivar, Weed, and the Plasticity of Plant-People Relationships
The scientific name of the tiger nut is Cyperus esculentus. It has tough, fibrous foliage and produces yellow flower heads where thousands of seeds can be found. Because of these features, they are often mistaken for grass. However, C. esculentus is a sedge that is identifiable by its triangular and waxy stems. Still, sedges are viewed as "grass-like weeds". While C. esculentus does produce small and plentiful fruits, they are not usually consumed. Instead, the most commonly consumed part of the plant is its tubers or the tiger nut. The tiger nut is commonly cultivated in North Africa, the Middle East, and Spain, where it is used as a food crop as well as feed for livestock. While these regions continue to regard the crop as beneficial, other places such as North America, Oceania, and Japan have opposing opinions on the invasive species.
C.esculentus is a perennial sedge found in tropical and subtropical regions. C. esculentus reproduces mainly through tuber formation, which produces exact clones of the parent plant. The plants also sexually reproduce through wind pollination. The small yellow flowers can cross pollinate and self pollinate, and can form seeds, though the seeds are not consumed. The clonal nature of reproduction through tuber proliferation allows C. esculentus to establish rapidly. The plant prefers wet, warm environments, such as bogs and marshes. C. esculentus have potential origins in multiple regions around the world, but the cultivated tiger nut most likely originated in the Mediterranean and Northern Africa. The plant belongs to the family Cyperaceae, which includes important crops such as water chestnuts and papyrus reeds. This family is part of order Poales, which includes widely cultivated crops such as rice and sorghum, as well as other common plants such as grasses.
Before they were seen as invasive weeds, the tiger nut was a highly valued crop. The earliest records of the tiger nut come from ancient Egypt where they were entombed with high-ranking Egyptian officials. The tuber could be used to make oil that was perfect for perfume and medicine, the leaves were useful to feed livestock, and they were even a great source of food. The tiger nut could be eaten raw, ground-up as flour, or roasted. One of the more common ways of processing the tiger nut was to make them into tiger nut cakes. A tomb-painting dated from the 15th century BCE illustrates the process of preparing tiger nut cakes from raw tiger nut. In this process, the large piles of tiger nuts are ground up into coarse flour which is then mixed with honey or oil. The mixture is then formed into long cones. These cakes were brought as sacrifices to the gods on an official’s behalf.
The use of the tiger nut spread to other parts of the world after the North African Moors invaded Spain in 711. With them, they brought the practice of drinking tiger nut milk. From this time, the Spanish began making horchata de chufa, chufa being the Spanish name for tiger nut. This transfer of goods only furthered after Spain colonized parts of Mexico. The Spanish conquistadors brought with them many of the components necessary to make horchata de chufa but forgot the main ingredient: tiger nut. So the earliest settlers used rice to make the horchata instead. To this day these popular drinks are still consumed as they were originally made today. The beverage, although varied by region, originated from the use of the tiger nut. The tiger nut is still cultivated in these regions of the world today, but they have managed to establish throughout the world as an invasive species.
In the 19th century, C. esculentus’ value as a crop species began diminishing. Plantation style agriculture has begun to be widely adopted throughout the world, with crops with the highest yields becoming more favored to support the growing global population. However, tiger nuts do not have a great yield per acre, and so remained a niche product due to perceived inefficiency.However, despite its lack of popularity as a cultivar, C. esculentus’ morphological traits and life history, including its ability to reproduce through rhizomes, tubers, and seeds, has made the plant an extremely effective invasive species in many parts of the world. When C. esculentus is viewed as a pest species, it is known by another colloquial name: the yellow nutsedge. Yellow nutsedge quickly dominates native plant communities due to how fast they propagate and their wide range of environmental tolerance. They often invade areas near bodies of water but can then propagate outwards to dryer areas. These wetlands, such as riverbanks and marshes, are extremely threatened biomes and also extremely valuable areas of agricultural development.
Many of the world’s heavily irrigated crops, such as rice, cotton, and onions, are grown in conditions highly favorable to yellow nutsedge propagation. Yellow nutsedge can easily outcompete these crops, grow quickly, and shade over them. Their rhizomes can penetrate the tubers and tap roots of crops such as potatoes and carrots, potentially destroying these crops. Uncontrolled yellow nutsedge infestations can lead to total loss of certain crops. Most management recommendations for yellow nutsedge involve rotating crops and utilizing competitive, taller crops to exploit the yellow nutsedge’s low shade tolerance. Corn, soybeans, and tomatoes are all possible candidates.
Interestingly, yellow nutsedge has also become a key part of management strategies for another invasive pest species: the carp. Carp has become an especially problematic conservation concern in many waterways around the world, and management agencies have turned to recreational anglers to help with the problem this species poses. The tuber of yellow nutsedge, used as the edible tiger nut, can also be used as bait to attract carp. The tubers are usually boiled and soaked before being used as either scatter bait or hook bait. Yellow nutsedge is attractive to carp but not as attractive to other wildlife in the other area, allowing for targeted removal of carp. In this way, an invasive species could potentially be used to control the numbers of another invasive species.
