Ecologist Suzanne Simard famously says that trees are “social creatures.” Like humans, they converse with one another, help each other out when in trouble, and even form bonds. One of these bonds is called inosculation. It’s when two trees fuse along their trunks or branches.
Scientific explanation
When the trunks of two individual trees start to join and grow together via inosculation, the effect is both romantic and intimate. The word inosculation is Latin for “to kiss” or “to unite.” The trees look like entwined lovers, leading to the quirky nickname, “the husband and wife tree.”
Beech tree trunks conjoined. Photo: Peter Hermes Furian/Shutterstock
While it looks unusual, it is not as rare as you’d think. Inosculation occurs predominantly with thin-barked species like elm, apple, maple, beech, olive, ash, and hazelnut.
Two trees — mainly of the same species — grow nearby and eventually meet when the wind blows them against each other. When they touch, they wear away their bark. Over a slow process that takes many years, the trees naturally graft together and create spectacular formations.
What happens is akin to how the human body heals its wounds. As the bark scrapes away, the wounded trees expose underlayers called phloem, xylem, and cambium.
The cambium is the most important. It is essentially tissue containing vital growth cells. To heal itself, the tree produces another tissue called callus. This acts as a protective scab covering the exposed cambium. The callus grows until it meets the neighboring tree trunk or branch. The two sort of glue together, sealed with sap.
Tree inosculation in Spain. Photo: Adwo/Shutterstock
This remarkable union allows the wounded trees to exchange nutrition, including water and sugars. In this way, a forest acts as a kind of big ecological family. These conjoined trees can symbiotically transfer energy from a healthier to an injured one. Inosculation also helps vulnerable trees get stronger in harsh weather.
Cultural background
Various cultures attached symbolism to this phenomenon. Not surprisingly, some associated joined trees with love, fertility, and marriage. In Greek mythology, Zeus turned an elderly couple named Baucis and Philemon into two entwined trees when they died. Indian temple grounds are full of these inosculated trees between which wedding ceremonies take place.
Inosculation vs grafting
Inosculation occurs naturally so you should not confuse it with artificial processes like grafting, pleaching, braiding, or tree shaping. Grafting refers to the horticultural practice of deliberately joining the tissues of two individual trees or plants so that the two can growth together. This process takes just 12 to 18 months, while inosculation requires years.
There are numerous reasons for grafting, including repairing injured trees, preventing disease, and creating hybrid species.
You can also find many different methods with which to join trees or plants together. A famous example of grafting is the combination of white and pink cherry blossoms in Japan. When grafted, the two trees exchange DNA and genetically become one. Meanwhile, two inosculated trees remain individuals.
Pleaching and braiding are tree-shaping practices associated with aesthetics. You train trees to grow in a certain way, particularly when you want to create a hedge. You can braid branches or wines or plant trees in a straight row so the branches grow into each other. Pleaching is particularly popular in royal gardens.
