Bertholletia excelsa - The Brazil Nut


B. excelsa is a member of the angiosperms, which is a group of seed plants that develop flowers and fruiting bodies to cover their seeds.  The flower of B. excelsa is zygomorphic, which means that it only has a single plane of symmetry dividing the flower into two equal halves.  What makes the flower of B. excelsa interesting is the fact that very few organisms can actually pollinate it due to the petals being tightly pressed against the androecium.  This seal can only be broken by organisms that are small enough to fit on the flower, but strong enough to pry their way in.  The most common organism to pollinate the flower is an orchid bee (many different species found throughout multiple genera).  Similar to many flowering plants, the pollinator (in this case, the orchid bee) feeds on the nectar within the flower, which consequently leads to the bee picking up the flower's pollen.  Eventually, the pollen will make its way to the flower of a different B. excelsa tree, completing the pollination stage of the life cycle.


Once fertilization is complete, the seeds and tough fruiting body start to develop.  After approximately fifteen months of development, the Brazil nut fruit is fully developed.  The fruit falls from the tree in an attempt to disperse the seeds; however, the fruit structure of B. excelsa is extremely tough and thick, so the fall from the tree is not enough to break open the fruit.  The tough fruit is what makes seed dispersal such a complex process because it requires aid from another organism to get through the shell.  This problem is solved by the intervention of a rodent, usually an agoutis, strong enough to chew through the shell and get to the seeds.  After acquiring the seeds, the rodent stores any uneaten seeds by burying them.  Once buried, the seeds are free to grow and complete the B. excelsa life cycle.


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Peter Zepke of University of Wisconsin - La Crosse.  BIO 203 - Spring 2012.