The stressed vowel in marchentia
heard as marchentia
spelled marchantia
Marchantia. The stressed vowel is a.
What the ear did
Even a stressed vowel goes uncertain when the syllable ends in n, which is why so many English speakers cannot hear the difference between -ant and -ent at the end of a word. The surname settles it.
M-A-R-C-H-A-N-T-I-A
The full entry for marchantia covers the name itself.