Someone typed marchansha. What has changed?
heard as marchansha
spelled marchantia
Only the ending. The ch is right and the -tia has been written as it sounds. It is Marchantia.
What the ear did
This is the most revealing of the heard spellings, because it shows a writer who knows the ch and does not know the ending. The -ia is the standard Latin suffix for a genus named after a person, and it has been attached to hundreds of surnames since Linnaeus made the practice universal: Fuchsia for Leonhart Fuchs, Dahlia for Anders Dahl, Marchantia for Nicolas Marchant. The t in front of it belongs to the surname, or rather to the Latinised form Marchantius, and it is the t that shifts to a sh sound in an English mouth. Nothing about that shift is visible. If you know the name is a person, you can reconstruct the spelling from the surname and the suffix without hearing either of them clearly, which is the only reliable route into a name like this one.
M-A-R-C-H-A-N-T-I-A
The full entry for marchantia covers the name itself.