a doubled consonant
Is it asplenium or asplennium?
One n. The fern is asplenium.
a doubled consonant
The extra n comes from where the weight of the word falls. Say it and the stress lands on SPLEE, hard enough that the consonant after it seems to arrive twice. English spelling does normally double a consonant after a stressed syllable, so writing asplennium is a reasonable guess about an English word. This is not one. The stem is Greek and the ending is Latin, and neither of them has any reason to double an n.
The class
A consonant doubled to mark a stress, the way English words do it.
Same name
The name