Late December, 2017

In an earlier post I mentioned the banyan trees in Old San Juan had been particularly hard hit by Hurricanes Irma and Maria. It turns out I was a bit premature in making that statement, for a couple of reasons.

Now, I must admit, I don’t know much about trees. This has been a source of some embarrassment, especially given my pre-retirement position as a faculty member at the New York State College of Environmental Science and Forestry. Many times, when making conversation with strangers, they would ask where I worked. They usually got all excited when I told them. Their eyes lit up, and they said “Oh great. I have this tree in my backyard . . .” When I told them I did  not know much about trees, they looked at me quizzically and said “Well then, what do you do there?” When I replied that I might know a bit about water, they invariably said “That’s not the problem. The tree gets plenty of water.”

This happened to me again and again, in coffee shops, dive bars and pre-symphony cocktail receptions. I vowed to learn more about trees, but I admit I never got around to it. I was just too busy building my wall. My willful ignorance has now come back to haunt me, in the form of banyan trees.

I first noticed what I thought was a banyan tree in a botanical garden on the island of Dominica. I vaguely recalled they were native to the Indian sub-continent. It was there with a Norfolk pine (from Norfolk Island, in the southwest Pacific, another introduced species) and several other specimen trees as well.

I recognized trees I thought were banyan trees in several places around San Juan.  I learned that many of these trees have been introduced to tropical areas around the world as ornamental trees. In fact, Parc Luis Munoz Rivera, across the street from our building, is known for its many banyan trees. They line some of the walkways and provide welcome shade to the park goers. I have, on occasion, sat on a bench under the canopy of what I thought was a  banyan tree and thought great thoughts, or at least my version of great thoughts. The botanical problem is they may not have been banyan trees, at least in the strictest use of that term.

Banyan trees are examples of fig trees, and fig trees have been around for a long time. Some biblical scholars argue that a fig, and not an apple, was the forbidden fruit in the Garden of Eden. The Latin words for apple and evil are the same: malum, and it may have been the Latin bibles that spread during the Middle Ages that caused the change of fruit in the creation story.

 Mithra, a Persian deity and Judge of Souls, was born under a fig tree, and figs were his first meal. In Kenya, the Kikuyu’s creation story starts in a grove of fig trees. On Guam, ancestral spirits (taotaomonas) live in the roots of fig trees. In Australia, aboriginal peoples know of the yara-ma-yha-who, a man-like vampire that lives in fig trees and preys on unwary travelers.  The Greeks have multiple stories concerning fig trees. In one, the fertility goddess Demeter created figs to repay King Phytalus for his help as she sought Persephone, her lost daughter.

Some time during the sixth to fourth century BC, a prince was born to a royal family in what is now Nepal. As he matured, Siddhartha Gautama began to wonder about the sickness and death he saw all around him. He left his home, wife and child at the age of 29 to wander the world in search of meaning. He studied under wise men but was not satisfied with their teachings. Six years into his journey, he arrived at a forest in what is now the  Indian state of Bihar. He sat under a fig tree and vowed not to leave until he reached inner peace. According to legend, he stayed there for six days and six nights; on the seventh day he found enlightenment and became the Buddha. He taught a Middle Way between sensual indulgence and the strict asceticism of his time.

Somewhat later, around 325 BC, Alexander the Great, having conquered most of the known world, turned his attention to India. As a scholar as well as a military leader, Alexander brought naturalists with him. They were intrigued by what they discovered – colorful birds, monkeys, exotic snakes, but nothing matched their interest in the banyan tree, large trees with multiple trunk-like roots. Alexander’s colleague Nearchus estimated 10,000 soldiers could get shade from one banyan tree.Alexander and his retinue of naturalists brought news of the unusual tree back to Athens where the Greek philosopher Theophrastus, a student of Aristotle, learned of it. Theophrastus (371 – 287 BC) had already become intrigued by figs; he observed carefully the trees that produced edible figs and noted that the soil and climate and tiny insects seemed to determine the quality of the figs. His observations were sound in this and other matters; he is known as the father of modern botany. He described the banyan tree: “The Indian land has its so-called “fig tree”, which drops its roots from its branches every year . . the fruit is very small, only as large as a chickpea, and it resembles a fig.’

Theophrastus did not call the fig tree from India a banyan tree; that came later. Portuguese traders noticed that the Hindu merchants (banya in the Gujarati language) they dealt with gathered under the fig trees described by Theophrastus. The Portuguese used banya for the merchants but it was soon generalized to became the name of the tree under which the merchants gathered.

The Swedish botanist, physician and zoologist Carl Linnaeus (1707- 1778), the father of taxonomy, denominated figs into the genus Ficus, with species names as appropriate. The banyan tree became Ficus benghalensis; the fig tree under which Buddha sat Ficus religiosa; the edible fig Theophrastus studied Ficus carica.  Linnaeus named seven Ficus species. There are now more than 750 known Ficus species.

Systematic taxonomy is one thing, but understanding the life cycle and ecology of fig trees another. One mystery was that fig trees, while producing a fruit-like fig, never seemed to display flowers. Ancient Hindu and Buddhist texts used the phrase ‘seeking flowers in a fig tree’ as we use looking for a needle in a haystack. A Tamil language proverb describes how a fig tree’s ‘flowers bloom secretly and fruits flourish visually’. We now know a fig is a hollow ball, the inner surface of which has flowers that never see daylight. How these flowers get pollinated and produce seeds is a complex and fascinating story In itself.

Like all plants, fig trees have evolved ways to put energy into making seeds, and strategies to aid in their dispersal. Fig trees have co-evolved with insects, usually fig wasps, relatives of the small insects Theophrastus observed. When a fig ripens, a female fig wasp, only about 2 mm long, responds to some unknown cue and emerges from a small hole in the fig. She is laden with hundreds of fertilized eggs and she must find a fig tree of the same species. She also carries pollen from the flowers within the ripe fig.

Her journey is perilous. Upon first emergence, predatory ants and other insects lay in wait. If she is able to take flight, she has to contend with other predators – dragon flies, bats, birds. The fig trees emit a combination of chemicals unique to its species; the fig wasp navigates towards them and thus finds the correct species of fig tree. Each species of fig tree has one, rarely two, species of fig wasps adapted to its reproductive needs.

The flight of some fig wasps have been shown to be as long as 160 km – awesome for an insect only 2 mm long, but it is the last centimeter of her travels that are the most crucial. The wasp lands on a fig less ripe that the one she left, and locates a tiny hole at the tip. She pulls herself into the fig, shedding her antennae and wings in the process, and using her wedge like jaws to assist. Once inside the fig, and assuming no predators lie in wait, she walks along a carpet of fig flowers. Some get pollinated, into others she deposits a fertilized egg. The pollinated flowers produce one seed each; the others become nurseries for the larval forms of the wasp’s offspring.

After some weeks, the larvae, one per egg-bearing flower, reach sexual maturity. The males live a short life; they burrow out of their galls and find a gall with a female inside. They use a tube on their abdomen to drill through the gall and deliver sperm to the female. Some species of fig wasps are active pollinators – a male, after inseminating the female, uses its jaws to harvest the pollen-bearing stalks of the fig’s male flowers. As the females emerge, they use their forelegs to harvest the pollen and store it in pollen pockets, cavities on their chest.

The females, now laden with eggs and pollen, need to emerge from the fig to start the cycle again. The males, in their last act, team up and chew a hole in the fig’s wall. The males emerge first, perhaps sacrificing themselves to predators to increase the female’s chances of survival. The females emerge and, if all goes well, fly away to another fig tree, leaving behind a fig with seeds ready to be dispersed.

Each fig species has evolved its own pollination strategy. In some, the male and female flowers are on different trees. In others, the pollination is passive, almost by accident, rather than the active pollination described above. But however the fig seeds become pollinated, they need to be dispersed. Again, various strategies have evolved to meet this need. And fruit-eating animals play a crucial role.

The ripe figs, with their payload of seeds, are a source of food for many animals, some of which help disperse the seeds. Green pigeons, for example, eat figs but their gizzards grind the seeds to nothingness. Other animals, gibbons, orangutans, flying foxes (really bats), many birds species, eat the figs and the seeds pass unharmed through the digestive tract, to be dispersed with their feces. One spectacular fig-eater and seed dispenser is the rhinoceros hornbill, native to Borneo.

The location of the dispersed seed is crucial. Take, for example, Ficus stupenda, a fig tree native to Malaysia. This species begins life as an epiphyte and so the seed has to land in a knothole, crock, crack, crotch of a host tree, with appropriate moisture and organic matter. And the height on the host tree is important with different optimal heights for different fig species. The seed germinates by sending a shoot up with two leaves, and a root down the trunk of the host tree into the soil. Shoots beget shoots, roots beget roots, and soon the fig tree becomes established. Some epiphytic figs grow so many roots and branches they strangle the host tree and have earned the name strangler fig. Ficus benghalensis, the true banyan tree, is an example of a strangler fig.

So I wondered what kind of trees I had been seeing. Clearly, they were not true banyan trees. It turns out there are three species of figs introduced and found in Puerto Rico, all of which are often planted as ornamentals for shade in public plazas. The most common of these is Ficus retusa, characterized by a short runk and globular crown, small, dark green, elliptical leaves, and numerous aerial roots about the trunk. Some of them might be Ficus elastica, also known as the India-rubber fig.

So know I know, or at least think I know. I was sitting under a fig tree, not a true banyan tree, and neither was it the same kind of tree Buddha sat under. That goes a long way in explaining why my  excuse for great thoughts will never be as profound as his. At least, that’s my current theory.

Notes and Sources: See Wikipedia entries for banyan tree, fig wasp, fig tree, fig tree pollination.

Much of the information about fig trees and their natural and cultural history is from Gods, Wasps, and Stranglers, a delightful series of essays by Mike Shanahan, a tropical forest ecologist. It is available from Chelsea Green Publishing, White RIver Junction, Vermont. It was published in 2016.

Identification of the fig trees in Puerto Rico is from Common Trees of Puerto Rico and the Virgin Islands, by Elbert Little and Frank Wadsworth. It was published by the US Department of Agriculture in 1964, as Agriculture Handbook No. 249. Thanks to my neighbor Lucilla Marvel for loaning me her copy.