asplanium or asplenium?

The e is the letter in this word that carries the meaning. Asplenium is Greek: a- for not, splen for spleen, because the fern was thought to act on that organ. English called it spleenwort for exactly the same reason, so the two names are one idea written twice, and both of them keep the e. Change it to an a and the spleen falls out of the word.

An unstressed vowel, flattened until it gives the ear no information.