Avocado Trees and Fruits: Botanical and Historical Facts - Owlcation - Education
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Avocado Trees and Fruits: Botanical and Historical Facts

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about living things.

Young leaves, flowers, and flower buds of an avocado tree

Young leaves, flowers, and flower buds of an avocado tree

Interesting Plants and Delicious Fruits

Avocado trees produce appealing and nutritious fruits with a buttery texture and flavor. Their fruit is not their only claim to fame. They have some interesting botanical features and a historical background that includes some intriguing facts. The fruits are a popular food in many places, including North America, but avocado plants are worth studying for more than their use as food.

The scientific name of the avocado is Persea americana. (The word "avocado" is used for the plant as well as its fruit.) The plant belongs to the family Lauraceae. The family includes other culinary plants, including the bay laurel (Laurus nobilis), whose leaves are known as bay leaves and are used to flavor food, and trees in the genus Cinnamomum, whose inner bark is used to make the spice known as cinnamon.

An avocado tree on Reunion Island, which is located east of Madagascar

An avocado tree on Reunion Island, which is located east of Madagascar

The Avocado Tree

Mature avocado trees are often thirty to forty feet tall. The height depends on the cultivar, however. So-called "dwarf" cultivars exist that reach only ten feet in height. On the other hand, some trees may be as tall as eighty feet. Though many avocado trees are cultivated in order to satisfy people's desire for the fruit, wild ones still exist. The trees may have a long lifespan. They can live for seventy to a hundred years or more, at least in their wild form.

The tree's leaves have an elliptical shape, as shown in the photo below. They are often arranged in loose whorls. The leaves are usually attached to the stem in an alternate pattern and have a glossy sheen. The plant is evergreen, but it sheds some of its leaves if it's stressed. Individual leaves are also shed due to old age and then replaced by new ones. New leaves are red at first and become green as they mature. In some cultivars, the leaves have a wavy edge.

Bark, mature leaves, and fruit of an avocado tree

Bark, mature leaves, and fruit of an avocado tree

Flower Facts

Flower Structure

The flowers are arranged in branched clusters known as panicles. They are often pollinated by bees. They have an interesting and unusual feature. Each flower has female and male reproductive structures, but depending on the time when it's open, the flower is functionally either a female or a male. When the flowers first open, they are female. When they open for the second and final time, they are male.

When a flower is in its female form, it has stamens with anthers, but the anthers are closed and can't release pollen. When the flower is in the male form, the anthers open up and release pollen, but the stigma of the pistil doesn't accept pollen grains.

Type A and B Flowers

The flowers are classified as either type A or type B based on their specific cultivar. The types behave differently with respect to flowering time.

  • Type A flowers open in the morning, when they are female. They close at noon. On the afternoon of the next day, they open again. At this time, they are male.
  • Type B flowers are female in the afternoon. They close in the evening. When they open the next morning, they are male.

The two types complement each other when they are grown near one another. When one type is male and releasing pollen, insects can pick up the pollen and deposit it on the stigma of the other type, which is female. The different stages of the flowers promote cross-pollination. Trees that are cross-pollinated produce more fruit than ones that are self-pollinated.

A close-up view of Persea americana flowers

A close-up view of Persea americana flowers

Avocado Fruits and Seeds

The fruits of the different cultivars are pear shaped or globular. Their color ranges from bright green to dark purple. Some versions have a smooth appearance and others a pebbly one. An alternate name for the fruit is "alligator pear." The pale yellow or greenish-yellow flesh is the part that's eaten. The seed is discarded.

The fruit is very nutritious and is rich in monounsaturated fat, vitamins, minerals, and fiber. It also contains omega-3 fatty acids. Monounsaturated fats are healthy for us (when eaten in reasonable and not excessive quantities). The cut flesh of the avocado fruit is popular on its own or as a component of a meal, as a spread in sandwiches, as the major part of a guacamole spread or dip, and even in desserts.

Biologically, the fruit is a berry. It matures on the tree but ripens off the tree. The dropped or picked fruit produces ethylene gas, which causes it to ripen. It contains a single seed, but this seed, or pit, is very large. Some people keep one or more seeds from their fruit in order to grow an avocado plant. A special procedure is needed for this activity. It's described in the Missouri Botanical Garden reference provided at the end of this article.

Origin of Avocados

Avocado plants have had a long history and have been grown for their fruit for a long time. Their origin is uncertain, but it's thought that the first trees that could be called "avocados" appeared in south central Mexico. Exactly when this happened is unknown. The species spread through Central America and eventually into South America. The history of the plant contain contains some interesting highlights. I discuss some of them below.

Avocados and the Pleistocene Megafauna

The Pleistocene Megafauna

Avocado plants seem to have thrived during the time of the Pleistocene megafauna (or the Pleistocene megaherbivores). The megaherbivores were a large group of herbivorous animals that inhabited North and South America, Europe, and other areas during the Pleistocene Epoch. The animals each weighed over a hundred pounds. They would have been impressive to see. Somewhat mysteriously, they became extinct as the epoch approached its ending around 13,000 years ago. The extinction happened at a different time in each area.

Wild Avocados in the Pleistocene

The wild avocado in the time of the megafauna produced a fruit with a large seed covered with a relatively thin layer of flesh. The wild fruits of today still have these features. The thick-fleshed fruits that many people love to eat arose during cultivation.

Avocados probably depended to a large extent on the megafauna for the existence of their species during the Pleistocene. Only big animals with a digestive tract of a large diameter could have safely passed the fruit and its large seed through their body, digested the flesh, and then deposited the seed in a suitable habitat in their feces. The process would have enabled the seed to germinate in a new area and grow into a new plant.

Extinction of the Megafauna

The Pleistocene is sometimes known as the Ice Age. Glaciers extended through North America and into South America (and through Europe). Not everywhere was covered by ice, however, and the glaciers repeatedly advanced and then retreated as the climate cooled and warmed.

The changes in the climate are believed to have been severe and rapid as the end of the Pleistocene approached. The stresses that occurred during this period are thought to have played a role in the extinction of the megafauna. Some researchers suspect that as the death of the animals started and their effects on their surroundings disappeared, conditions in the environment may have changed in a way that was deleterious for the remaining animals. It's believed that the increasing number of human hunters were also part of the reason for the extinction of the megafauna.

Effects of the Megafauna Extinction

Avocados are sometimes said to be "anachronistic plants" or "ghosts of evolution" because it seems that they should have become extinct long ago when the megafauna disappeared.

Without the aid of the megafauna, the fruits of an avocado tree would have dropped under the parent tree and (assuming nothing else ate their flesh) decayed. If the seeds inside were exposed before they began to decay, they may have been blocked from light by the leaves of the parent tree. Modern avocado trees can produce dense shade. Assuming this was also the case in the Pleistocene, the shade would have interfered with the growth of any seedlings that emerged from the seeds.

The scenario described in the previous paragraph is commonly mentioned and may well have happened, but it can't be the whole story. Avocados didn't become extinct at the end of the Pleistocene, and both wild and cultivated ones exist today. They were obviously able to reproduce and spread in the wild without the aid of their former megafauna helpers, though perhaps to a lesser extent. Exactly how they survived after the ancient megaherbivores disappeared is unknown.

It's possible that humans collected some of the fruits, ate the flesh, and discarded the seeds without eating them. At some point, people decided to deliberately plant the seeds. They likely chose seeds from fruits with the thickest flesh in an attempt to produce more of them.

The Grafting Process in Plants

A very common cultivar in North America today is the Hass avocado. The history of Hass avocados involves an attempt at grafting. This process is often performed by commercial growers of fruit trees, including avocados. It involves joining parts of two different plants together in order to increase the probability of rapid production of high quality fruit with uniform characteristics. The parts that are joined are referred to as the scion and the rootstock (or the stock).

Various styles of grafting exist. Many factors are involved in creating a successful or unsuccessful graft, and there are some biological unknowns about what happens during the process. The basic process can be summarized as follows.

  • The scion is a cutting that is capable of producing buds and comes from a tree with desirable features. (The rest of the tree is left to continue its life.)
  • The rootstock is the part of a plant that produces roots and comes from a plant variety or species that is compatible with the scion. The rootstock is grown from a seed and often contains a short stem and sometimes leaves as well as roots.
  • The scion and rootstock are carefully joined together so that they become one plant.
  • The stock supplies the new plant with water and nutrients. The new branches, leaves, flowers, and fruit that form from the scion will have the genes and features of the desirable plant.

Grafting is a type of asexual reproduction of desirable plants, albeit one that is controlled by humans. As might be imagined, the scion and rootstock must be chosen carefully, and they must be joined correctly in order to ensure that vascular tissues meld and that a successful union is obtained.

Growing new plants from seeds would be a slower process than grafting and would have an uncertain outcome with respect to the fruit's features. The quality of the fruit wouldn't be known in advance.

The grafting process in a dahlia and a woody plant in 1911

The grafting process in a dahlia and a woody plant in 1911

History of Hass Avocados

Rudolph Hass (1892–1952) was a US letter carrier who lived in California. In 1926, several types of avocados were grown in California. Hass was already growing avocados in his garden (reportedly the Fuerte cultivar) at the time of the discovery for which he is remembered. The general points in the creation of the Hass avocado are known, but some of the details are a bit fuzzy.

Hass bought avocado seeds of an unrecorded and probably unknown type from a seed collector. He hoped to grow rootstocks from the seeds to join with scions from his favorite Fuerte avocado plant (or plants). He tried more than once to graft a Fuerte avocado scion onto a particular stock created from one of the purchased seeds, but his attempts failed.

Hass ignored the rootstock after his failures and found that it continued to grow by itself and produce a tree. He was surprised that the tree eventually produced fruit with an unusual appearance. The Hass cultivar produces fruit at the relatively young age of two or three, so "eventually" wasn't very long. Hass discovered that he and his acquaintances liked the taste of the fruit.

Hass patented the cultivar, which became very popular. Unfortunately, patenting didn't have as much value then as it does today. Hass made very little money from his discovery.

A Delicious Food and a Resilient Plant

I didn't discover avocados until I was an adult and had lived in Canada for some time. Now I can buy an avocado from my local grocery stores any time I want to. The fruits are always available. I love their taste and texture. The fruits that I eat are often Hass avocados, because they are what my local stores most often sell. I occasionally see other types of avocados, though, and plan to gradually explore them. I enjoy exploring the avocado plant's biology and history as well as the taste and uses of its fruit. It's an interesting and impressive plant in more ways than one.

References and Resources

  • Avocado fruit and tree information from the Encyclopedia Britannica
  • Avocado flowering and pollination from Gary S. Bender, University of California Agriculture and Natural Resources
  • Persea americana facts from the Missouri Botanical Garden
  • Nutrients in commercial avocados from SELFNutritionData (The data is obtained from the USDA, or United States Department of Agriculture)
  • "Why the Avocado Should Have Gone the Way of the Dodo" from K. Annabelle Smith, Smithsonian Magazine
  • Anachronistic fruits from Connie Barlow and the Arnold Arboretum, Harvard University
  • Megaherbivores and avocados by Jeffrey Miller, Colorado State University
  • Plant grafting information from Jing Wang, Libo Jiang, and Rongling Wu, New Phytologist journal
  • "How the Hass Avocado Conquered the World" by Brian Handwerk, Smithsonian Magazine

© 2020 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on August 30, 2020:

Thanks, Rajan. I appreciate your visit and comment.

Rajan Singh Jolly from From Mumbai, presently in Jalandhar, INDIA. on August 30, 2020:

This is a very interesting and educative read. Thank you for sharing.

Linda Crampton (author) from British Columbia, Canada on August 25, 2020:

Hi, Kathi. It is sad that Hass didn't get the credit that he deserved. Hass avocados are so popular today. Thanks for the visit.

Kathi from Saugatuck Michigan on August 25, 2020:

So interesting about the history, Linda, I love avocados, like so many. Wish I could grow a tree where I live in Michigan, but it's too cold here and they just die in the winter. I also wish Hass could have made the money he hoped to.

Linda Crampton (author) from British Columbia, Canada on August 17, 2020:

Hi, Rachel. I think avocados are interesting and delicious. Thanks for the visit, Blessings to you, too.

Rachel L Alba from Every Day Cooking and Baking on August 17, 2020:

Hi Linda, I love avocados. That was the first time I saw an avocado tree. I actually didn't know how they were grown and always wondered why they were called Hass avocado, now I know. You actually do learn something new every day. Thanks for all of the information.

Blessings to you

Linda Crampton (author) from British Columbia, Canada on August 13, 2020:

Thank you very much for the comment, Mel. I'm looking forward to reading your article! It's sad when people don't get the rewards that they deserve.

Mel Carriere from San Diego California on August 13, 2020:

Yippee! You just gave me an idea for another one of my Legendary Letter Carriers series. Another mailman here who vanished into humble obscurity and then people made tons of money off of his discovery.

Brilliant use of history with the avocado here, and tying it in with the megafauna. Because I live in Southern California I tried to grow an avocado, but I think I had it in a bad spot that was too shady and it never really took off. I understand that their cultivation is a tricky art, and getting fruit from them is fickle unless you really know what you are doing. Unlike Haas I have other hobbies, so I think I will leave avocado growing to the experts and just enjoy the ones we buy in the supermarket. My wife is Mexican so you betcha we eat a lot of them.

Great work.

Linda Crampton (author) from British Columbia, Canada on August 10, 2020:

Thanks for the comment and for sharing the information about the climate where you live, Rajan.

Rajan Singh Jolly on August 10, 2020:

Enjoyed reading about the lesser-known facts of avocado. Unfortunately, it does not grow in North-India as it cannot tolerate the extremely hot weather as well as the frosts here.

Linda Crampton (author) from British Columbia, Canada on August 09, 2020:

Hi, Ken. I think it would be very nice to grow avocado trees in a garden. I'd love to pick the fresh fruit. Thanks for the visit.

Ken Burgess from Florida on August 09, 2020:

Great article, have been living in Florida for five years now, have been growing our own Avocado trees, unlike our pineapples we will have years to go before we reap the results.

Linda Crampton (author) from British Columbia, Canada on August 09, 2020:

It must be nice to have so many avocados in the stores. I always see them in my local grocery stores, but there's never a large collection of them. I appreciate your comment, Adrienne.

Adrienne Farricelli on August 09, 2020:

I love avocados! My home is near the Mexico border and we get lots of them in grocery stores. Thanks for pointing out the danger of persin to pets.

Linda Crampton (author) from British Columbia, Canada on August 03, 2020:

Thanks, Flourish. I appreciate your visit and comment a great deal.

FlourishAnyway from USA on August 03, 2020:

Excellent, detailed information about the avocado plant. I learned quite a bit about the plat. You always do such a thorough job presenting your information.

Linda Crampton (author) from British Columbia, Canada on August 01, 2020:

Thanks for the visit and for commenting, Nithya.

Nithya Venkat from Dubai on August 01, 2020:

Interesting and informative article about the avocado plant. The type and A and B flowers of the avocado plant help the tree to propagate it’s species efficiently. I enjoyed reading the historical facts, thank you for sharing.

Linda Crampton (author) from British Columbia, Canada on August 01, 2020:

Thank you very much for the visit and the comment, Fran.

fran rooks from Toledo, Ohio on August 01, 2020:

What a wonderful, detailed article!. Avocados are delicious and very healthy. Your photos add detail to your article. Thanks for your info.

Linda Crampton (author) from British Columbia, Canada on July 31, 2020:

Thank you, Mark. I would love to attend an avocado festival.

Mark Tulin from Santa Barbara, California on July 31, 2020:

Thank you for taking me on the trip through avocado land. It was certainly worth the price of admission. I live in California and have gone to the avocado festival in Carpinteria.

Linda Crampton (author) from British Columbia, Canada on July 31, 2020:

Thanks for the visit and for sharing the information, Dora. I'm sorry that you had to get rid of your avocado tree, though I can certainly understand why you did it.

Dora Weithers from The Caribbean on July 31, 2020:

We had to get rid of our avocado tree, for fear that the root grew too close to the foundation of the house. They are common in my neighborhood and often they are infested with termites. Still there is so much that I did not know about their origin and history. Thanks for the information.

Linda Crampton (author) from British Columbia, Canada on July 31, 2020:

Hi, Ann. I appreciate your comment. I'm going to buy an avocado very soon. I've noticed that my nearest supermarket has two cultivars that I've never tried before.

Ann Carr from SW England on July 31, 2020:

Interesting with so much detail, Linda. I had no idea about the Types A and B, nor about its history regarding the Pleistocene period. You've told us a lot about other animals and plants too.

I also love the taste and texture of avocado. It adds so much to a salad, or a dip and has the bonus of being nutritious.

Thanks for the education.

Ann

Linda Crampton (author) from British Columbia, Canada on July 31, 2020:

Thanks for sharing the information, Devika. It is a unique fruit. I think the plant as a whole is interesting.

Linda Crampton (author) from British Columbia, Canada on July 31, 2020:

Hi, Imogen. Thanks for the comment. Avocado plants grown from seed may not flower for many years. depending on the type of avocado. Self-pollination in avocados does occur at times, but the trees are far more likely to produce fruit if they cross-pollinate. You would need to know the flower types of the two trees to make it worthwhile to plant a second one if your goal is fruit production, though.

Devika Primić from Dubrovnik, Croatia on July 31, 2020:

Hi Linda South Africa is the other popular country for many fruits including Avocados it is delicious. Unfortunately, Avocados do not grow in Croatia. Informative hub about a unique fruit.

Imogen French from Southwest England on July 31, 2020:

A really interesting article Linda. I didn't know avocados went back to the Pleistocene era. We are trying to grow one in our polytunnel here in England - we grew it from seed and it's now about six years old. Although it looks healthy enough and is about 5ft tall it hasn't yet flowered. After reading what you said about the male/female flowers I wonder if I ought to grow a second one to help with pollination, if it ever flowers!

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thank you, Urooj. I think the information linked to avocados is very interesting.

Urooj Khan from Karachi, Pakistan on July 30, 2020:

This hub is very much informative. It is quite fascinating to know about Avacado.

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thank you for such a kind comment, Liz.

Liz Westwood from UK on July 30, 2020:

This is a fascinating and extremely detailed article, packed with interesting information. Next time I eat avocado, I shall view it in a new light.

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thank you, Pamela. It must have been lovely to pick an avocado any time you wanted to!

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thanks for the visit, Peggy. I always appreciate your comments.

Pamela Oglesby from Sunny Florida on July 30, 2020:

I really like avocados and it is great to learn the history of the trees. I sure didn't know about the huge sloths.

I lived in CA a long time ago but we had a huge avocado tree hanging over in out yard so we could have an avocado any time. It was great. This article is full of great information and I found it very interesting.

Peggy Woods from Houston, Texas on July 30, 2020:

We love eating avocados, and most often purchase ours from Costco. Your information about the height of the trees, ice age sloth, and Rudolph Hass added to my new-found knowledge. Thanks!

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Hi, Denise. The story of Rudolph Hass is interesting. I'm looking forward to exploring more types of avocados.

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

I appreciate your comment, Linda. I think avocados are interesting as well as delicious.

Denise McGill from Fresno CA on July 30, 2020:

I enjoy avocados too. I didn't know about this story, so once again, you have educated me. In the future I will have more respect when I see the Hass name on my avocado.

Blessings,

Denise

Linda Chechar from Arizona on July 30, 2020:

I'm crazy about avocados. I usually have at least an avocado once a week. I had no idea there were huge sloths in the Ice Age! Your article is full of great information!

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thank you for the visit and the comment, Danny. I love avocados, too. I think they are a delicious fruit.

Danny from India on July 30, 2020:

Very informative article. By the way, I love avocadoes.

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Hi, Heidi. I like your idea about why the avocado survived! Thanks for the visit.

Heidi Thorne from Chicago Area on July 30, 2020:

I think the avocados survived because the Pleistocene creatures discovered how to make guacamole and chips. :-D

Hubby loves avocados and guac, but I've never attained a taste for either. But it is an amazing and nutritious fruit.

Thanks for sharing these fun food facts!

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

I appreciate your visit, Moondot. Thank you very much for the comment.

EK Jadoon from Abbottabad Pakistan on July 30, 2020:

Alicia, here in Pakistan we can't find Avocado easily but no doubt it's a delicious fruit and your article is very informative. I also have a bachelor's degree in botany that's why I'm interested in these topics. Stay blessed.

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thank you very much, Eric.

Eric Dierker from Spring Valley, CA. U.S.A. on July 30, 2020:

We love our Avocados here is San Diego. I found that so interesting about the ice ages. Thanks

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Hi, Liza. I love avocados, too. I don't eat them every day because they can be quite expensive, as you say. They are delicious, though!

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

That's interesting information, Bill. Thank you very much for sharing it.

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thanks, Louise. I love the fruit as well. It's unusual but delicious.

Linda Crampton (author) from British Columbia, Canada on July 30, 2020:

Thank you for the comment, Thelma. I think it would be lovely to have an avocado tree in the garden. It's a shame that the plant causes problems for some animals.

Liza from USA on July 30, 2020:

Hi Linda, I love avocado, last night I just ate it! I love the taste and the texture of the avocado. Almost every weekend, I bought avocados, for salad, and also for my hair treatment. However, avocado is quite expensive, as it is one of the superfoods in the world. I remember watching a documentary on Netflix about avocado. After reading your article, I noticed Haas Avocado, one they have mentioned in the show. Thanks for sharing Linda. I learned a lot!

Bill Holland from Olympia, WA on July 30, 2020:

Great information! I was listening to an NPR story on the radio about the avocados in California, how they require two bee hives per tree, and how the beehive business is huge because of that....fascinating stuff! Did I hear that correctly?

Louise Powles from Norfolk, England on July 30, 2020:

That was really interesting to read. I love avacado's.

Thelma Alberts from Germany and Philippines on July 30, 2020:

Wow! There are lots of information on this article about avocado. My father planted avocado in our yard years ago and the tree is bearing a lot of fruits. I didn't know until now that the avocado fruit, leaves and seeds are dangerous to our pet. Thank you very much for sharing.

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