The fruit commonly called a “sycamore seed” belongs to the Sycamore Maple, Acer pseudoplatanus. This fruit is not a simple seed but a specialized, winged structure known as a samara, a term used for the dry, wind-dispersed fruits of all maple species. The samara’s design is an adaptation that allows the enclosed seed to be carried far from the parent tree.
Anatomy of the Sycamore Samara
The sycamore samara is a double-winged fruit, consisting of two separate winged units joined at their bases. Each unit has two main parts: the seed case (or nutlet) and the papery wing (the ala). When developing, the samara is often pale green or yellowish-green.
As the fruit matures in late summer and autumn, the color shifts to a dry, light brown or tan. The seed case is a small, rounded, and slightly flattened capsule containing the seed. Extending from the seed case is the fibrous, translucent wing, which feels papery and is marked by distinct, fine veins.
The typical length of the entire sycamore samara ranges between one and two inches. A defining characteristic is the angle at which the two wings diverge. In the Sycamore Maple, the wings usually form an acute angle, spreading apart at approximately 90 degrees.
How They Are Grouped and Dispersed
Before release, sycamore samaras are attached to the branches in long, hanging clusters called pendulous racemes or panicles. These clusters hold numerous pairs of the double-winged fruits, creating a distinct appearance on the tree in the fall. The fruits ripen and detach from the tree around September and October.
Upon detachment, the samara employs a dispersal method known as autorotation. The asymmetrical weight of the seed case, combined with the broad, angled wing, causes the fruit to spin rapidly as it descends. This spinning action generates a miniature vortex of air, similar to a helicopter rotor, which significantly slows the rate of fall. This reduced speed allows the wind to catch the spinning samara, carrying the seed over greater distances. Due to this characteristic spinning motion, these fruits are often colloquially referred to as “whirlybirds” or “helicopters.”
Distinguishing Sycamore Seeds from Other Samaras
The winged fruit of the Sycamore Maple is one of many similar samaras produced by other maples. A primary feature for differentiation is the angle formed by the two wings. The Sycamore Maple’s near 90-degree angle is distinct from the nearly horizontal, 180-degree spread seen in the Norway Maple samara.
It is also important to differentiate the Sycamore Maple samara from the fruit of the American Sycamore, Platanus occidentalis. Despite sharing a common name, the American Sycamore does not produce a winged samara. Its seeds are small, hairy achenes clustered tightly within a spherical, woody structure known as a “buttonball” or seed ball. These buttonballs hang and break apart to release their fuzzy, parachute-like seeds in the late winter or early spring.