not sure on the chromosome count of beccarii, thought it was the same as M. coccinea. Regardless, making tetraploids of all of these would possibly eliminate some of the barriers caused different chromosome numbers. There are already crosses like this with other, less attractive species
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I'm attaching a photo of M. beccarii fruits, nothing in the photo for comparison but they are 6-7 inches long, and weren't even fully ripe in this photo.
Tim C.