The ginkgo tree is a popular choice for urban landscaping due to its resilience and distinctive fan-shaped leaves that turn a brilliant yellow in autumn. While many people notice the yellow, plum-like objects that fall from some of these trees, there is a common misunderstanding about what they are. Ginkgo biloba trees do not produce true fruit. The structures that drop from the female trees are technically naked seeds, a distinction rooted in their ancient botanical classification.
Understanding the Ginkgo’s Classification
The reason the ginkgo structure is not a fruit lies in its botanical classification as a gymnosperm. True fruits are exclusively produced by flowering plants, known as angiosperms, and are defined scientifically as a ripened ovary containing seeds.
Ginkgo trees lack flowers and therefore do not have an ovary to ripen into a fruit. As gymnosperms, they belong to a more ancient division of plants that reproduce using “naked seeds” that are not enclosed within an ovary wall.
The structure that falls from the tree is an ovule that develops a fleshy outer layer called the sarcotesta. Beneath this soft, apricot-like sarcotesta is a hard, stony layer that encases the edible ginkgo nut. This entire assembly is a seed with a specialized coating, making it structurally distinct from true botanical fruits.
The Origin of the Distinctive Odor
The distinctive smell associated with the ginkgo’s reproductive structures is entirely due to the fleshy outer layer, the sarcotesta. This layer contains specific chemical compounds released when the structure is crushed or begins to rot on the ground.
The primary compound responsible for the strong, off-putting scent is butanoic acid, commonly known as butyric acid. This organic acid is also found in substances like rancid butter and certain aged cheeses. The odor results from the breakdown of fats within the sarcotesta.
The smell serves a biological purpose, attracting animals that would eat the fleshy coating and subsequently disperse the hard inner seed. For humans, the fallen seeds create a slippery mess, and the pungent smell can be overpowering in urban environments. The sarcotesta also contains ginkgoic acid, a compound known to cause allergic contact dermatitis in sensitive individuals.
Why Gender Matters for Planting
Ginkgo trees are a dioecious species, meaning individual trees are distinctly male or female. Male trees produce small, odorless pollen cones in the spring. Female trees produce the ovules that develop into the smelly, seed-bearing structures in the autumn.
This reproductive separation is the foundation for urban planning. Landscapers and city foresters prefer to plant only male trees, using clones propagated through cuttings to guarantee the tree will never produce seeds.
Planting male-only cultivars avoids maintenance issues and public complaints caused by the rotting material from female trees. Accidental planting can lead to a surprise problem decades later, as females may not begin producing seeds until they are 15 to 20 years old. Selecting male trees allows cities to benefit from the ginkgo’s attractive foliage and robust nature without the seasonal nuisance.