Favoritos de carlinaon

C. fragilis (edit: and C. tenuis) also possible due to the dark brown stipe. No bulblets observed. Earlier petioles not observed to be particularly red or maroon. Growing from a crack in a north facing vertical limestone face next to a cave opening from which a spring flows.

Growing on the north side of a ~1905 rock wall.

Characteristics that indicate Woodsia:
"petioles scaly at maturity" (Steyermark Flora of Missouri, vol 1)
"Plants form a loose clump, the old stem bases persisting to the next year, broken off at varying points so are of varying lengths." (MinnesotaWildflowers.info)
"Woodsia has the final veinlets not reaching the margin; Cystopteris veins do reach the margin." (Weakley Flora of the Southern and Mid-Atlantic States)
[Final veinlets are not reaching the margin in this observation. Zoom into the fourth photo for the best view.]