Yohanan,
I have a seedling just like that;it was from a batch of open pollinated
Musa acuminata malaccensis that might have had genetic admixture with two "acuminata" accessions from Assam, India more than 6 decades ago.
It looks just like your plant - including the undulant leaf margins; undersurface colouration; and I suspect the peculiarities of leaf venation.
It came as a complete surprise to me! The other seedlings were mostly typical. Not at all this divergent!
I'll get photos when next I visit my seedling gardens next week.
Maybe you could keep me in the loop about your seedling's development? It would be very interesting to compare notes.
shannon
shannon.di.corse@gmail.com