Alex wrote:
"Thus "a" versus "u" or versus "o" appears to be a regular reflex if
the original vocal in the IE word was an "o" ( the short one so far I
remember). "
I agree that it could be too from a short "o" in some of the cases.
However there is a really a-u alternance also :
Rom. 'muma' (
http://dexonline.ro/search.php?cuv=muma&source=)
(popular variant).
versus Rom. 'mama' 'mother'
( Please remember also that "Muma Padurii" a mythological person
eng. 'Forest's Mother' is never "Mama Padurii" in Romanian even DEX
indicated both forms at
http://dexonline.ro/search.php?cuv=mama&source=)
We have also a-a a-u present in other variants for mother : 'muica'
versus 'maica'
http://dexonline.ro/search.php?cuv=muica&source= )
Also regarding Albanian we have your (very good) example :
Alb 'lyth' versus Alb. 'lajthi' (in my opinion both derived from
the same common word alanjc- / alunic-) that shows this alternance
inside Albanian too.
I will come back with other Romanian and Albanian examples regarding
this alternance in the evening.
Only the Bests,
marius