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During the past decade, students and faculty in the Life Sciences Department at Palomar College have taken some marvelous field study expeditions to tropical regions of the world. We have explored the beautiful beaches of many countries, from Mexico, Central America, and the Caribbean Islands to the Galapagos Archipelago and French Polynesia. One of the most fascinating topics that evolved out of these exotic study trips is the origin of all the countless seeds and pods that are washed ashore on remote tropical beaches. Hundreds of species of flowering plants routinely travel the world's oceans with their unique drift disseminules, their destination in time and space at the mercy of the wind and currents. But of all the drift seeds, one of the most remarkable is the Mary's bean (Merremia discoidesperma). In addition to being one of the most unique and unmistable drift seeds, it also has the greatest documented drift range of any species on earth.

The Mary's bean comes from a little-known tropical vine or liana in the morning-glory family (Convolvulaceae). Named after the Virgin Mary, it is also called crucifixion bean because of a cross etched on the dorsal side of the seed. The ventral side has a large, oval attachment scar (hilum). The cross is actually an impression where the seed was attached inside the capsule. Part of the cross is produced by the impression of a narrow, black strap that is connected at each end of the hilum. The strap wraps around the dorsal side of the large seed and holds it in the papery outer capsule.

In all other Merremia species, the cross is divided into a tetrad of four small (separate) seeds. New Mary's bean seeds still enclosed in their capsules are covered with a dense layer of black hairs. The fuzzy covering eventually wears off exposing the dark brown-black, woody seed coat that is impervious to water. The thick seed coat and internal air cavities enable the buoyant seeds to drift for months or even years at sea.

Historically, people have used Mary's beans as good luck charms and to ward off evil spirits. A woman in labor was assured an easy delivery if she clinched a Mary's bean in her hand, and the seeds were handed down from mother to daughter as treasured keepsakes. The seeds have also been used as an antidote for snake bites in Nicaragua and as a cure for hemorrhoids in Mexico. The hemorrhoidal treatment requires the sufferer to carry a "male" and a "female" seed in their back pocket. Apparently the sex of a seed is determined by whether they float or sink in water. According to the "Flora of Guatemala" by P.C. Standley and J.A. Steyermark (Fieldiana Vol. 24, 1946), "male" and "female" seeds from another rain forest liana Mucuna argyrophylla are carried by natives to prevent hemorrhoids. Those that sink in water are called "hembras" (female) and those that float are "macho" (male). They are also called ojo de venado (deer eyes) and "sea beans" because, like the Mary's bean, they often become drift seeds. To this day, Mary's beans are sometimes sold by street vendors in Costa Rica, although I am not sure which of the above purposes they are used for. Throughout beaches of the Old and New World, the Mary's bean is always a treasured discovery for beachcombers lucky enough to find one.

My first encounter with a Mary's bean was on the Caribbean island of Grand Cayman. After searching diligently for one along the beaches, a strange "olive" with a faint cross etched on one side turned up in my martini one evening, a gift from my students. On subsequent trips to the shores of Belize and Costa Rica I found other Mary's beans, but I could never find the plant that produced these fascinating drift seeds. It wasn't until my trip with marine biologist Lester V. Knapp to the lush rain forests near Golfito, Costa Rica that I finally found the parent of these unusual seeds.

In its native habitat, the Mary's bean vine or liana is only known from a few locations in the rain forests of Mexico and Central America. In the rain forest near Golfito, Costa Rica, scattered Mary's bean vines hang from the trees, forming dense curtains of leafy stems typical of morning glory vines. Other woody lianas of the legume family (Fabaceae) also grow in the area, including several species of sea beans (Mucuna spp.) and the amazing sea heart (Entada gigas). The latter leguminous vines also produce remarkable sea-faring seeds (the subject of other Noteworthy Plant articles). The seeds commonly get washed down rivers where they drift out to sea. As a drift seed, the Mary's bean is known from Wotho Atoll in the Marshall Islands to beaches of Norway, a total distance or more than 15,000 miles (24,000 km). According to the world authority on drift seeds, Charles R. Gunn (Economic Botany Vol. 31, 1977), this is the widest drift range documented for any seed or fruit. Other pantropical seeds (such as sea beans and sea hearts) may drift as far or farther, but their precise point of origin cannot be determined. According to Nancy and Brian Vander Velde (Drifting Seed 10 (2), September 2004), a Mary's bean was found on Bikini Island, Bikini Atoll, Marshall Islands. This latest documented location is 90 miles (150 km) to the northwest of Wotho Atoll. The Mary's bean is unmistakable among drift seeds and its origin is well documented. If you find one, it must have ultimately come from the rain forests of southern Mexico and Central America.

Several other twining vines with tuberous roots and beautiful yellow, funnel-shaped blossoms also belong to the genus Merremia. During the late spring and summer in the scenic Cape region of Baja California, the endemic species called "yuca" (M. aurea) decorates the native vegetation with striking golden trumpets.

Another similar species of Merremia (M. tuberosa) grows in the Hawaiian Islands and throughout the tropics. Known to Polynesian travelers as the "wood rose," the enlarged, dried calyx surrounding the seed capsule resembles a lovely rose carved in wood and polished to a satiny-brown finish. Inside the papery capsule are four black seeds that neatly fit together like a cake cut into four sections. All four pieces together are roughly the size and shape of one Mary's bean.

The fabulous Mary's bean has many special meanings to different people. To me it brings back fond memories of wonderful field trips to the tropics, and especially my dear friend and colleague, great teacher and naturalist, Lester Knapp. And to beachcombers everywhere: May a Mary's bean brighten up your life if you happen to discover one of these most unique and truly remarkable drift seeds.

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