Secret Sex Life of Ferns - Spores on Birds Nest Fern Leaves
I believe this is some form of bird's nest fern (genus Asplenium), though I'm not 100% certain. I'm about 99% certain it is a fern of some kind, and the dark reddish brown areas are spores.
DP077-2015 Posted Wednesday, March 18; processed Mar. 17 from photo taken Mar. 16.
The view is from beneath and/or behind the leaves, looking directly at the undersides of the leaves. There were several new fronds uncurling, and they didn't have the brown streaks, so they definitely are things that form as the fronds mature.
Tropical Dome, Conservatory at Hidden Lake Gardens, Michigan
Title: Secret Sex Life of Ferns - Spores on Bird's Nest Fern Leaves