Ilex guayusa (pron.: / / or / /) is an Amazonian tree of the holly genus, native to the Ecuadorian Amazon Rainforest. One of three known caffeinated holly trees, the leaves of the guayusa tree are dried and brewed like a tea for their stimulative effects.
The guayusa plant is a tree growing 6–30 meters tall. The leaves are evergreen and 2.5–7 cm long. The flowers are small and white. The fruit is spherical and red, 6–7 mm in diameter. The leaves contain caffeine and other alkaloids.
Biological descriptions 
The plant yields xanthines such as caffeine. Two other species of holly trees, Ilex paraguariensis, or yerba mate, and Ilex vomitoria, or yaupon holly, also contain caffeine. A tall tree native to the upper Amazonian regions of Ecuador, northeastern Peru, and southwestern Colombia, guayusa has been collected only rarely by botanists is known almost exclusively as a cultivated plant. Melvin Shemluck documented a flowering guayusa tree in Pastaza Province, Ecuador in his work between 1979 and 1980.
Cultivation and use as a beverage 
The plant is grown primarily in Ecuador in the eastern provinces of Napo and Pastaza, but is found in parts of Peru and Colombia. After harvest, the guayusa leaves are dried which allows flavor to develop.
Traditionally, some Ecuadorian Kichwa people boil guayusa leaves in water and consume the resulting beverage for its stimulative effects. In addition to drinking cups of guayusa like many Americans drink coffee, indigenous hunters drink guayusa to sharpen their instincts and call it the “Night Watchman" because it helps them stay alert and awake all night. Fresh leaves are used as well as dried leaves, which are dried in rolls and strung together as a wreath resembling a Hawaiian lei.
Chemical composition and properties 
In addition to caffeine, guayusa also contains theobromine, a stimulant commonly found in chocolate, and L-theanine, a glutamic acid analog found in green tea that has been shown to reduce physical and mental stress.
Chemical analyses in 2009 and 2010 have shown caffeine content in guayusa of 2.90-3.28% by dry weight. Guayusa contains all of the essential amino acids for humans and has a “high antioxidant activity,” with ORAC antioxidant values of 58μM per gram, compared to 28-29μM per gram for commercial green teas.
There have been few published studies on the possible medical benefits of guayusa, but one study has shown that ingesting guayusa helped reduce hyperglycemia and other side-effects of Type 1 diabetes in an animal model.
"Wayusa" as spelled in the indigenous Kichwa language of the Ecuadorian Amazon. Also pronounced "Why-sa" by the Kichwa people and "Why-ees" by the Shuar people.
Myths and legends 
Michael Harner, the founder of the Foundation for Shamanic Studies describes how “the Jivaro say guayusa is so habituating that before it is offered to a visitor, he is warned that once he drinks it, he will ever always after return to the Ecuadorian Jungle.”
A 1,500-year-old bundle of guayusa leaves was found by Harvard University ethnobotanist Richard Evans Schultes in a medicine man's tomb high in the Bolivian Andes, far beyond the natural range of the plant.
See also 
- Ilex paraguariensis - A caffeinated holly known commonly as Yerba Mate
- Ilex vomitoria - A caffeinated holly used to make the Black Drink
- Kuding - A holly from Asia which is used as a type of Tea.
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- To assess antioxidant capacity of Guayusa (Report). Center of Studies of Biological Research and Evaluation (CEIEB in Spanish) Pharmacy and Food Institute Universidad de la Habana. 2010. http://www.scribd.com/doc/61535352/Guayusa-FRAP-Study-English-Translation.
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