I was referring to the precious 'dwarf' forms of M.cauliflora, precoe or hibrida and very similar more red fruited form red jaboticaba as identified by Lorenzi in the Brazilian Fruits book. By contrast the Scaret or escarlette is not in the book and physically appears to be much more similar to M.areana and seems likely to be a areana hybrid.
Adam I am in the right hemisphere at least and was speculating on what it could be. This species is highly plastic and contains varieties paulista and pnhema and not all have the depressed central vein. If it is a hybrid there may be a chance one of the M.cauliflora varieties is a parent.