Sea-Bean Identification: Five Types to Compare

A beach-found seed is easier to identify when you look beyond its color. Compare its shape, thickness and surface, then find the hilum, the scar where the seed was attached inside the fruit.

These five groups give you a starting point. They are not a complete key to every drift seed on Florida beaches. Our sea-bean overview explains the wider beachcombing context.

Sea heart

Sea hearts are associated with Entada gigas in Caribbean and western Atlantic collecting references. The name comes from the outline, but individual seeds vary: do not expect every one to resemble a perfect Valentine heart.

Compare the broad faces, edge and overall profile with the sea-heart guide. A heart-like outline is a clue, not proof by itself, and a polished reference specimen can look different from a weathered find.

Hamburger bean

Hamburger beans are seeds of Mucuna species. The rounded faces and conspicuous band around the edge suggest a bun with a filling. That band is a seed scar, not a joint between separate halves.

Compare the width of the band, the seed's thickness and the shape of the area where the band ends. Color alone is not enough to name a Mucuna species. Use the hamburger-bean guide as a starting comparison.

Mary's bean

Look for the distinctive cross-shaped groove pattern on one side of a dark, rounded seed. A description such as “small and spherical” misses the useful identifying feature.

Older references call this plant Merremia discoidesperma; you may also see Decalobanthus discoidespermus. Kew's current Plants of the World Online accepts Distimake discoidesperma. These names help you connect references to the same plant rather than assuming each name describes a different find.

Photograph both sides: the diagnostic mark may be hidden in a single view.

Nickernut

The grey nickernut, Guilandina bonduc, has a hard, smooth, rounded seed. Compare it with the grey-nickernut entry, paying attention to the seed scar as well as its marble-like shape.

Older guides place nickernuts in Caesalpinia. Kew accepts Guilandina bonduc and Guilandina major for the grey and yellow nickernuts discussed in these references. Treat common names and color as starting clues rather than assigning every pale round seed to one of them.

Sea purse

Sea purses can resemble hamburger beans. Specialist comparison photographs show useful differences in the flattened upper outline, edge shape and relative width of the hilum. Examine those features together rather than using “lighter brown” as the test.

Older drift-seed guides use Dioclea names. For example, Kew now treats Dioclea reflexa as a synonym of Macropsychanthus comosus. A sea-purse-like find need not be identified to species from one photograph.

Make a useful identification record

Photograph both faces and the edge beside a ruler. Keep the original images and location note even if you later revise the name.

Do not taste unknown seeds or fruits, and keep them away from children and pets. If the visible features do not match confidently, “unidentified drift seed” is a useful label. There is no need to force every find into one of these five groups.