Small ferns with their roots in a crack. Three genera, all named in Greek, none of them spelled the way it sounds.
The ground
A fern growing out of mortar has to be small, tough and dry-tolerant, and the three genera here are all of those things. Asplenium wedges itself into limestone and old walls across most of the northern hemisphere. Cheilanthes holds out on hot dry rock where almost nothing else fern-shaped survives. Woodsia lives on mountain ledges and is scarce enough in Britain to be protected.
The names
a-SPLEE-nee-um
Asplenium trichomanes
Nine hundred or so species of small ferns, most of them living in cracks. The name is the reason English calls the family spleenworts, and the four syllables run past quickly enough that.
5 recorded spellings
ky-LAN-theez
Cheilanthes lanosa
The lip ferns, small and often furry, holding out on hot dry rock. The name puts three Greek spelling conventions in a row and is the hardest word on this site to write down from the sound.
14 recorded spellings
WOOD-zee-uh
Woodsia ilvensis
A small genus of mountain ferns named after a person, which makes it the one name on this site you can spell from a fact rather than from a rule.
9 recorded spellings
Worth noting
Two of the three names describe an organ: a spleen the plant was thought to treat, and a lip that the frond margin makes over its spores. The third is a man's surname with a Latin ending bolted on. Knowing which is which is most of the spelling.
Elsewhere