By Galyna Vakulenko on March 18, 2019
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.
Other posts in the series: ginkgo biloba, Douglas fir, giant sequoia, Chinese tallow, silver-dollar gum, Monterey pine, green dracaena, coast live oak, cork oak, Japanese maple, silver birch, dawn redwood, Japanese persimmon ‘Hachiya’, carob, and California bay.
The avocado is one of the most popular foods in the United States. Within California, the rich fruit is so commonplace that it is a symbol of the California lifestyle. Underneath the avocado’s dark skin lies a delicious fruit and some fascinating history.
The avocado (Persea americana) is a lush evergreen tree that is native to Mexico and grows to be 60 feet tall. It has long, dark leaves, similar to that of the bay laurel. It is well known for its fruit—a bright green, pear-shaped fruit with a large pit and covered in a dark bumpy shell. The word avocado comes from the Aztec word ahuacatl, meaning testicle, likely due to its appearance.
The fruit itself has a divisive taste—some people despise it and some live for it. Avocados have a higher fat content than any other fruit, giving them a much creamier taste. Many of these fats are monounsaturated fats, which are a staple of the human diet. Recent studies have shown that eating healthy fats have substantial health benefits. This has contributed to the recent popularity of the avocado.
Avocados are an example of evolutionary anachronism, meaning that they are adapted to survive with the help of an organism that has since gone extinct. Over 10,000 years ago, giant ground sloths used to roam across South and Central America. These beasts, the size of elephants, would eat avocados whole. The large avocado pit would pass through the digestive tract of the animal and be dispersed far from the original tree.
After the extinction of the giant sloths, the avocado fruit would simply drop down and compete with their mother tree for light and nutrients. The avocado would have gone extinct as well, if it had not been discovered by humans.
Since its discovery and domestication, modern avocados have been bred to have more flesh and smaller seeds than its wild relative. Avocados are difficult to breed, so the main technique for their propagation in agriculture is grafting, where the stem of the desired tree is joined to the roots of a different one.
Early on, avocados had a diverse range of shapes and sizes. In 1926, a Southern Californian mailman named Rudolph Hass purchased some avocado seeds to plant in his yard. The origin of the seeds is not known, but due to a lucky mutation, the tree grew up frost resistant and bearing richer, creamier fruit.
Due to its high yield, weather tolerance, and taste, the Hass cultivar became the dominant avocado cultivar around the world. The Hass avocado tree soon became the first tree ever patented. Today, over 80% of the avocados sold in the United States are clones and descendants of the original Hass mother tree.
The avocado is a versatile food. It is a common substitute for fat in vegetarian cuisine and it is used in savory meals and desserts alike. And due to its dependence on people for its propagation, the avocado is as in love with humans as we are with it.
Galyna Vakulenko was 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.