Where does the e come from in lunelaria?
heard as lunelaria
spelled lunularia
From the ear, not the word. It is lunularia.
What the ear did
An unstressed vowel is written with whichever letter the writer reaches for first, and e is the commonest of all. Latin has u in that slot because the diminutive is -ula.
L-U-N-U-L-A-R-I-A
The full entry for lunularia covers the name itself.