It is so wonderful — and quite relieving — to put 2020 behind us and begin a new year. It was not easy introducing isolation into our lives.
Perhaps like many of you, however, I found this solitude provided me a moment to reflect on my interests. I have always been learning about plants and sharing that knowledge with others.
To start the year off, we will look at a group of trees known for their stature: baobabs.
The common name for the genus Adansonia, baobab is derived from the Arabic “buhibab.” The eponym for Adansonia honors the French botanist Michel Adanson, who was one of the most important naturalists of the 18th century.
Though the first report of the tree comes from a 14th-century Arab traveler, Adanson observed this tree in 1749 on the island of Sor in Senegal and appeared to have been quite enchanted by it. During his time in Africa Adanson worked for the Compagnie des Indes trading company and made many plant specimens, which he used to write “Histoire Naturelle du Senegal.”
Though Adanson described this genus as Baobab in 1751, Linnaeus honored him by including it in his circumscription of Adansonia. Surprisingly the two had contrasting views on systems of classification. Clearly Linnaeus must have had some respect for Adanson to name such a magnificent tree after him.
Species of Adansonia can vary from 16 to 98 feet tall with relatively compact crowns. Its bottle-shaped trunk can have a diameter of 7 to 10 feet, or in the case of A. digitata, 33 feet in diameter. These long-lived trees — estimates vary from hundreds to thousands of years — are known for their ability to store water in the soft, concentric sheets of wood that make up their massive trunks.
There are currently eight accepted species that range from tropical Africa to the Arabian Peninsula (Yemen and Oman), Madagascar and Australia. The center of diversity for this group is Madagascar. One explanation for their distribution is a Gondwanan origin followed by subsequent speciation that occurred after the supercontinent broke apart.
However, DNA evidence indicates that the group achieved its current range well after Australia separated from Africa and Madagascar. So, baobabs most likely made it to Australia via a transoceanic dispersal event. This is possible since the fruit of all species are capable of being dispersed by water.
Another trait that all members of the genus share is a relationship with a nocturnal pollinator.
Baobab flowers often open close to sunset. They are white and generally have a musty to pleasant odor. Often this suite of characteristics, known as a pollinator syndrome, is indicative of bat or moth pollinators. Bats or bush babies pollinate Adansonia digitata, the most common species planted in Honolulu. Mammals, like nocturnal lemurs, frequent some species in Madagascar. The remaining taxa are pollinated by hawk moths.
If you want to observe nocturnal pollinators, you can plant our white-flowered hibiscus. There is the Oahu- endemic Hibiscus arnottianus, or H. waimeae, which is native to Kauai. These species are distantly related to baobabs since they are all in the Malvaceae, or mallow family.
If you are not able to grow a plant at home, there are plenty of Adansonia to observe around Honolulu. One of the most prominent plantings is outside of The Queen’s Medical Center. This tree was originally planted by Dr. William Hillebrand in 1859 and has been declared an “Exceptional Tree” by the state of Hawaii.
Jesse Adams is a botanist at the Harold L. Lyon Arboretum, where he works to catalogue, propagate and conserve the plant diversity found there.
