Same plant, usually Constata Romanesco is the preferred name. There are a few vendors Underwood gardens, Fedco, siskiyouseeds, etc call it Constata Romanesca. Some one familiar with Italian may be able to shed light on why the difference in spelling.

I bet the later (ending in "a" is correct). Spanish and Italian are pretty similar, using "a" for feminine and "o" for masculine nouns and adjectives. "Costata Romanesco" seems like a mismatch in gender. between the feminine noun "costata" and the adjective "Romanesco.

George
Tahlequah, OK