By Galyna Vakulenko on October 1, 2018
Tree Spotlight Series: Follow along as we learn about the fascinating trees that live among us. This series is in partnership with Rhee Lab in the Plant Biology Department of the Carnegie Institution for Science.
The coast live oak (Quercus agrifolia) is a large oak tree native to the Pacific Coast of California and is an important tree in California’s cultural landscape.
The coast live oak can grow to up to 80 feet tall. Its bark is thick and grows gnarled and deeply fissured as the tree gets older, with twisted and irregular branches. The live oaks are a group of evergreen oaks—they do not shed their leaves in the winter. In the spring, the oak produces small catkin flowers; the mild coastal weather ensures that the flowers can bloom for many months.
The coast live oak was an extremely important tree to the California Native Americans. The acorns produced by the oak were a primary food source of many native groups, including the Ohlone, Kameyaay, and Cahuilla people.
After harvesting the acorns, they were ground into a flour-like paste. The tannins (a bitter phenolic compound) from the acorns were leached out by placing the paste in a cloth bag and washing it in water several times. Traditionally, this was a private affair. No one else should look at the acorns as they were being leached since the tannins turn the water yellow. This was believed to cause embarrassment for the food and the acorns would always taste bitter as a result.
After leaching, the acorn paste was cooked and eaten as a mush called wiiwish. Additionally, the wood from the coast live oak was used to make spoons and bowls, and the red bark of the tree was used to dye clothing.
Acorns were not only a staple food to the Native Americans, but they are also eaten around the world. They have been used in soups and as substitutes for coffee in Europe and North America. Acorn noodles (made from acorn flour) are eaten in Korean cuisine, as well as acorn jelly, made from acorn starch. With the rise of factories and technology, it is no longer necessary to leach tannins for months. Now that acorn flour is much more readily available it has become a popular gluten-free flour to make breads and cakes.
The coast live oak was also used for more than just its acorns. Pioneers in the West used its wood to build fires and wagon wheels. The gnarled and twisted branches of the tree prevented it from being used for timber, but they were used by ship-builders to make specialized joints. The abundance of the oaks in the area did not go unnoticed. Coast live oaks (and their Spanish name Encino) are the namesake of California cities such as Oakland and Encinitas, a city near San Diego.
Like many California oaks, the coast live oaks are vulnerable to Sudden Oak Death, a recent disease caused by the plant pathogen Phytophthora ramorum. While the disease is not harmful to humans, it ravages oak forests and nurseries. To prevent the spread of disease, many California parks and oak forests have a brush to clean your shoes on to remove any spores before leaving.
Galyna Vakulenko is a 2018 summer intern at the Rhee Lab in the Plant Biology Department of the Carnegie Institution for Science at Stanford University. She is an undergraduate student majoring in plant physiology at Carleton University in Ottawa, Canada.