This genus is meant to have 2 species with an edible value: P.
aquatica and P. insignis. The specific food(s) produced by each species
is not clear. An edible nut described in all languages as chestnut,
almond, hazelnut, cacao, pistachio etc. is mentioned, but none really
compares to the others. So chosing a name more appropriate than the
others is problematic. The 2 plants also are aquatic but only one is
called aquatica ... today. In
the past both have been named aquatica.
So it looks like more work is needed to sort the useful species in this
genus.