cledonia, and the first syllable
heard as cledonia
spelled cladonia
It is a, from klados. Cladonia.
What the ear did
The first syllable is unstressed and quick, so the vowel is barely there to be heard. Every word built on the same Greek stem keeps the a: cladode, cladistics, Cladophora.
C-L-A-D-O-N-I-A
The full entry for cladonia covers the name itself.