Functionally indehiscent fruit

• Title

  Functionally indehiscent fruit

• Definition

  A circumscissile fruit that opens via an operculum (lid) but the seeds are trapped inside because the size of the opening is smaller than the size of the seeds.

• Notes

  In the Lecythidaceae, only Bertholletia excelsa has this type of fruit. When the fruits are ripe, the small operculum falls inside of the fruit and the seeds remain within the fruit when the fruits fall to the ground. In the past, this type of dehiscence was called secondary dehiscence but that term is now applied to all indehiscent fruits that appear to have evolved from dehiscent-fruited ancestors whether they are functionally dehiscent or not. In fact most of the other secondarily indehiscent fruits do not open at maturity, e.g., Lecythis gracieana, L. lurida, L. parvifructa, L. prancei, and L. rorida. A few species seem to dehisce their opercula under some conditions and retain them under other conditions.

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