The Ginkgo biloba tree, often referred to as a “living fossil,” is admired for its unique fan-shaped leaves and spectacular golden fall color, making it a popular choice for urban landscaping. While this ancient species offers aesthetic value and resilience against pollution, it is also known for a powerful, offensive odor that appears in the autumn. This unpleasant aroma is a significant source of complaint in city environments where the trees are common. Identifying the specific sex of the tree responsible for the stench is key to understanding this botanical mystery.
The Female Ginkgo is the Source
The answer lies in the Ginkgo’s reproductive biology, as the species is dioecious, meaning individual trees are distinctly male or female. Only the female Ginkgo tree produces the structures that cause the foul smell. Male trees solely produce pollen cones and are entirely odor-free. The odor does not come from the tree itself, but from the seed structure that drops to the ground in the fall.
Female trees produce a plum-shaped seed that matures into a yellow-brown, fleshy structure, often mistakenly called a fruit. This outer layer, known as the sarcotesta, is the source of the stench. The odor intensifies as the seeds fall, are crushed, and begin to decompose on the ground, creating a messy, slippery layer that can pose a hazard on sidewalks and streets.
The Chemical Behind the Rancid Smell
The intense, rancid odor is directly caused by the presence of butyric acid within the sarcotesta. This organic acid is known for its pungent smell, commonly described as similar to vomit, spoiled meat, or rancid butter. The concentration of this compound is highest when the seeds are freshly fallen and the fleshy coating is breaking down.
The production of butyric acid serves a biological purpose, thought to be an ancient mechanism for seed dispersal. While the smell is repulsive to humans, the odor was likely an attractant to specific animals in the Ginkgo’s prehistoric environment. These animals would consume the fleshy coating, and the hard inner seed would pass through their digestive tract, effectively dispersing the embryo away from the parent tree.
Selecting the Right Tree for Landscaping
Understanding the source of the smell is important for landscape planning, leading arborists and city planners to exclusively select male Ginkgo trees for planting. To ensure a tree is male and will not produce odorous seeds, nurseries cultivate male cultivars, such as ‘Autumn Gold’ or ‘Princeton Sentry.’ These are propagated asexually through grafting, which uses tissue from a known male tree, ensuring the resulting plant is genetically identical and seedless.
The sex of a Ginkgo seedling cannot be determined visually until it reaches sexual maturity, often between 20 and 50 years. This long waiting period makes planting non-grafted saplings a major risk for unintentionally introducing a female tree and its odor problem to an urban area. A rare complication is the occasional observation of a male tree producing female branches or undergoing a full sex conversion, possibly in response to environmental stress. This can unexpectedly introduce the malodorous seeds years after the tree was planted.