In an attempt to expand their territory, some well-armored tropical seeds and frutis hitch rides on ocean currents. These sea beans are often found on our beaches, with more than 150 different species seen from Cape Canaveral to the Keys.
1 After dropping from their parent trees, many sea beans wash into inland rivers that flow to the ocean, where they are transported by ocean currents to distant beaches.
2 Sea beans have pockets of air that keep them afloat for long periods of time, and their seed coat is often hard and impermeable to saltwater. Even so, many of these drifters become waterlogged and sink before they reach land.
3 The South Atlantic equatorial current, feeding into the Gulf Stream, carries seeds and fruits from Africa, including the sea heart, true sea-bean, sea purse and gray nickernut.
4 The Gulf Stream current, flowing north from South America and the Gulf of Mexico, deposits many sea beans on eastern Florida beaches.
5 Those that reach shore must overcome competition and foragers, as well as differences in moisture, temperature and soil conditions, to sprout and survive.
6 The Gulf Stream, which continues past North America, takes some seeds to the far-off beaches of northern Europe.
True sea-bean or hamburger bean
Mucuna spp.
Produced on vines, these seeds break out of pods that have tiny stinging hairs (not visible here) to discourage predators. In Africa, this sea bean is carried as a charm to prevent illness. The seeds may remain buoyant for one to two years and are among the most commonly found sea beans.
Gray nickernut
Caesalpinia bonduc
This species, native to southeast Asia, can be found throughout the Caribbean and in South Florida. It grows as a spiny shrub, forming dense thickets just above the high tide zone. The prickly pod houses seeds which are sometimes used as marbles (nicker is another name for marble). The seeds are also used as buttons, jewelry and in various remedies for controlling fevers and dysentery. They may drift for more than two years, with most of the seeds remaining viable.
Sea-coconut
Manicaria saccifera
Also known as a sleeve palm, this species is native to the American tropics. The fruit may contain one, two or three seeds and the species may be hard to identify depending on which layer of the fruit or seed is exposed. This sample shows a single weed with a partial fruit coat.
Mary’s bean
Merremia discoidesperma
This seed carries the distinctive mark of a cross on one side. Some think the cross gives the seed special meaning and protection to the owner. In some cultures, these seeds were passed down from mother to daughter to be squeezed during labor to ease delivery. The seed comes from a woody vine that grows in Guatemala, Chiapas, Mexico and Hispaniola. Although the seeds may be viable when washed ashore, seedlings in Florida usually are eaten by insects, preventing the vine from spreading.
Tropical almond
Terminalia catappa
This is one of the most common tropical drift fruits. Originally form tropical Asia, this species is grown for its edible seeds, which taste like almonds, and as an excellent shade tree. The outer covering is soft and corky, enabling it to remain buoyant at least two years. Half of the seeds that wash ashore may be viable.
Jamaican naval spurge
Omphalea diandra
These seeds were originally packed inside an orange-sized hard-shelled fruit that comes from a climbing shrub found along beaches, tidal swamps and rivers in the tropics of the Americas. As the fruit breaks open, the seeds are released and drift to the ocean. Unbroken seeds may float for two years, and half of these seeds may float for two years, and half of these may still be viable when they wash up on the beach.
Bay bean
Canavalia rosea
This species forms a thick tangled vine on beaches throughout the tropics. The seeds can drift and remain waterproof for up to a year and a half, and most are still viable when they was ashore.
Crabwood
Carapa guianensis
This species is a native tree of western hemisphere tropics, including South America and Guyana. The seed may drift for one to two years with about half remaining viable.
Blisterpod
Sacoglottis amazonica
Native to the South American Amazon and Orinoco River basins, these small trees produce unusually lumpy seed coverings. They may drift for two years and about 30 percent of the fruits contain a viable seed. Although the seeds often wash up along the shores of Jamacia and other Caribbean islands, they have not been successful there.
Black pearl
Sapindus saponaria
These trees are native to the American tropics. The seeds resemble black pearls and often are used to make necklaces. Crushed seeds have been used as fish poison and the fruit has been used as an astringent. The seeds may remain buoyant for 14 months, and seeds that wash up on Florida beaches from Cuba usually are viable.
Sea purse
Dioclea reflexa
Drifting from Asia, these seeds have reached shorelines throughout the tropics and successfully colonized those areas. Some seeds have washed ashore as far away as northern Europe by traveling with the Gulf Stream.
Coin plant
Dalbergia ecastaphyllum
This species occurs as trees, shrubs or vines found in mangrove swapmps in the tropics of the Americas. The wood from this species, known as rosewood, has many uses. Roughly 25 percent can remain viable after a nine-month trip.
Anchovy-pear
Grias cauliflora
Native to the American tropics, this tree grows along rivers or in marsh forests. The seed pods travel by river to the sea, where they may drift for one to two years. By the time they wash ashore, many ar dead or dying; only about 10 percent survive the journey.
Screwpine
Pandanus spp.
Not pines at all, these eastern hemisphere tropical plants have palmlike stems and bear an edible fruit resembling a pineapple. The roots and leaves are used for making ropes, baskets, mats and hats. The screwpine now is cultivated in sourthern Florida.
Sea heart
Entada gigas
Found in the Amazon, the Caribbean, Cuba and Hispaniola, this woody tropical vine produces long fruits with up to 15 individual compartments holding seeds like this one. Most of the seeds remain viable for the two years they may drift before washing ashore. Considered luck charms by many collectors, the seeds are often polished and engraved with artwork.
Starnut palm
Astrocaryum spp.
This species is native to tropical America and the West Indies. The husks that wash up on our beaches may have been drifting for two years and usually lacck a seed.
Antidote vine
Fevillea cordifolia
This high-climbing woody vine is found in fresh water swamps in the tropics of the Americas. The seeds may drift for up to two years and remain viable if undamaged. Seeds which germinate in fresh water will die when they reach the ocean, as they cannot tolerate salt water.
Cocoid palm
Orbignya cohune
These trees are natives of the Atlantic coast from southern Mexico to Central America. The leaves of the mature tree may be up to 60 feet long and 6 feet wide.
The seed, typical of palms, has three pores on one end that resemble a face. It may remain adrift for more than a year but usually lacks any viable seeds.
Manchineel
Hippomane mancinella
This seed comes from trees that form dense thickets along tropcial shorelines throughout the Caribbean and along the coasts of Central America and northern South America. Parts of this tree are very poisonous and the milky juice found in the fruits will blister skin. The drift seeds, which are harmless, may remain buoyant for up to two years with a 50 percent chance of viability.
Finding sea beans
When looking for sea beans, search the line of seaweed marking the normal high tide line. Also search the line of seaweed higher up the beach, where storm tides deposit material. Clean the seeds with soapy water or alcohol to remove oil and dirt. Seeds with hard coats can be polished using fine sandpaper or in a rock tumbler.
Growing sea beans
To try to grow a sea bean, make a small slice into the seed coat to allow fresh water to enter. Soak the seed in fresh water for 24 hours. Then plant it in potting soil to a depth of 1 or 2 inches. Seedlings of the sea heart, true sea-beans and the sea purse will emerge in about four weeks. if the seeds are viable.
SOURCES: Mary Barnett, Nova Center for Applied Research and Professional Development; Dr. Dan Austin, Florida Atlantic University; World Guide to Tropical Drift Seeds and Fruits by Charles R. Gunn and John V. Dennis; Grolier Multimedia Encyclopedia; Ocean Journeys by Mangrove Seedlings by Charles R. Gunn and John V. Dennis.
