Banyan Trees (Strangler Figs)
Species I’ve seen so far:
Ficus altissima (Council Tree)
F. microcarpa (Chinese banyan)
F. benjamina (Weeping Fig)
Growth and lifecycle
Ficus (Urostigma) spp. are large evergreen forest trees. “Evergreen” meaning they have leaves all year, not that they are coniferous, as the term sometimes implies in temperate regions.
Banyan figs start their lives as an epiphyte; their seeds germinate on the surface of another plant. This isn’t a parasitic relationship because epiphytes don’t draw any resources from the host, they draw moisture and nutrients out of the air. Strangler figs are technically hemiepiphytes, because once they begin to grow they send roots to the ground and begin to draw water and nutrients from the soil, thus ending their epiphytic stage.
Their roots will wrap around the host tree, thicken, and prevent secondary (outward) growth. This is where they derive the name “strangler figs”. By the time the fig tree has grown strong enough to support itself, it has usually dominated the canopy and suffocated the host. Once the host tree decomposes, the fig tree will appear as a hollow column of twisted stems. In other instances, however, the two species can co-exist and some hypothesize that the fig provides extra support to the host during the heavy winds.
In rainforests, there is high competition for sunlight and only a small percentage reaches the forest floor. The epiphytic life cycle allows plants to grow closer to the canopy where there is available sunlight and less competition. Where there is adequate sunlight, strangler figs can also germinate in the soil.
The Fig and THe Wasp
The Ficus genus is known for it’s unique method of fertilization. Each species relies on one or a few specific wasp species (fig wasps), which are also completely dependent on the fig species. The trees and wasps have co-evolved a specialized mutualistic relationship.
Fig trees can be monoecious of dioecious. Monoecious trees have both male and female flowers on the same tree, where dioecious trees are either male or female. Both types have life cycles which include a fig wasp, but for the purpose of this short summary I’m going to focus on monoecious trees.
Fertilized female fig wasps carry pollen into the unripe fig “fruit”, called the syconia, which can contain hundreds of flowers. They lay their eggs on the female flower while pollinating the fig. The female soon dies in the fig. The wingless male wasps emerge first and inseminate the emerging female wasps. The males then bore exit holes where the females exit, collecting pollen from the male flowers on the way, and begin their search for another fig flower.
Think about that next time you’re eating a ripe fig! The fruit releases an enzyme to break down the female wasp body, so you’re not actually eating a bug, only the nutrients from it’s body.
Fig wasps typically only live for a few days, so this process is rapid and continuous. Fig trees are keystone species in rainforest ecosystems because they supply a food source year-round.
With strangler figs growing quickly and overcrowding other species, the sound like they’d make a dangerous invasive species. The degree of specialization with the wasps, however, limits their geographical range. Unless a specific fig wasp is also introduced in the same areas, the trees won’t be able to reproduce.
Encyclopedia Britannica. Ficus, Plant Genus. Found HERE
Padmanaban, D. (2016). A tale of loyalty and betrayal, starring figs and wasps. BBC Earth. Found HERE
Machado, C.A., Jousselin, E., Kjellberg, F., Compton, S.G., Herre, E.A. (2001). Phylogenetic relationships, historical biogeography and character evolution of fig-pollinating wasps. Proc Biol Sci 268 (1468): 685–94. Found HERE