How many r's are in the name?

heard as marrchantia

spelled marchantia

One. marrchantia should be Marchantia.

What the ear did

Doubling looks right because the syllable break falls immediately after the r. The name is not built from English parts, so English syllable habits do not apply: it is Marchant with -ia added.

Sound decision: a doubled consonant under the stress. Said mar-KAN-tee-uh, often mar-KAN-sha.

M-A-R-C-H-A-N-T-I-A

The full entry for marchantia covers the name itself.

Other spellings people try

marchentia
marchansha
markansha
marshansha