polytrishum: which ch is this?
heard as polytrishum
spelled polytrichum
The hard one. Polytrichum is said with a k, not an sh.
What the ear did
The word carries a real fork in English spelling. A ch from French says sh, a ch from Greek says k, and a ch from Old English says the sound in church. Trichos, hair, is Greek, so the k wins.
P-O-L-Y-T-R-I-C-H-U-M
The full entry for polytrichum covers the name itself.