A sea bean is a seed or fruit from a terrestrial plant that has traveled across the ocean. These natural objects are sometimes called drift seeds or drift fruits, and they wash ashore far from their tropical origins. Their journey across vast stretches of water is a form of natural seed dispersal that has fascinated people for centuries.
The Biological Identity of Sea Beans
Sea beans originate from plants and trees that grow near tropical or subtropical waterways, often in rainforests bordering rivers. Many common sea beans are the seeds of woody vines, known as lianas. The most successful seeds have evolved a specialized protective anatomy that allows them to survive long-distance ocean voyages.
The outer layer is a tough, impermeable seed coat that prevents salt water from penetrating the embryo inside. This hard shell enables the seed to remain viable for extended periods. Beneath the shell, the seed often contains internal air pockets or a lightweight, corky material, which provides the buoyancy necessary to float freely.
How Sea Beans Travel the Ocean
The journey begins when the seed falls from its parent plant and is washed into a stream or river. Freshwater currents carry the seeds downstream until they reach the ocean. Once in the sea, they are captured by major oceanic circulation patterns, such as the powerful Gulf Stream.
These interconnected currents transport the buoyant seeds thousands of miles from their equatorial sources in South America, Central America, and the Caribbean. The combination of the seed’s air-filled structure and hard coating allows it to drift for many months without becoming waterlogged. Experiments show some specimens can remain capable of germination for over 32 years of constant immersion. The seeds typically wash ashore along the high tide line.
Identifying Common Sea Bean Varieties
Common sea bean varieties are often identified by their unique size, shape, and color.
- The Sea Heart (Entada gigas) is a large, flattened, dark mahogany-brown seed, measuring about 5 centimeters across, featuring a distinctive heart or kidney shape.
- The Hamburger Bean (Mucuna) is smaller and spherical, resembling a flattened disc. Its colors range from tan to nearly black, characterized by a dark band (hilum) around the circumference.
- The gray Nickernut (Caesalpinia bonduc) is a small, marble-like seed.
- The flattened, circular Sea Purse (Dioclea reflexa) is also frequently found.
Folklore and Modern Uses
The mysterious arrival of sea beans on distant shores inspired local folklore and legends for centuries. Before ocean currents were understood, people believed these seeds drifted up from underwater forests. The kidney-shaped Sea Heart was widely used as a good luck charm, especially by sailors, who saw its long journey as a symbol of protection.
In Scotland and Norway, the seeds, sometimes called “Mary’s Kidneys,” were traditionally carried by women as amulets to aid in childbirth. Today, collectors and artisans prize the seeds for their natural polish and durability. They are often drilled and strung to make unique jewelry, polished for decorative crafts, or kept as natural souvenirs.