from the January 24, 2010 Newsletter issued from
Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO
Beside one of Hacienda Chichen's pools the stone wall's interstices are luxuriantly and prettily colonized by the frilly, black-stemmed fern shown above.
Fern admirers will quickly recognize that this is a kind of maidenhair, because maidenhair fronds are three or four times compounded into small, confetti- like pinnae like those in the picture, held in place by slender, somewhat brittle, blackish stems. However, this clearly isn't any of the North's common maidenhairs, so who exactly is it?
Since the species occurs in Texas and thus is represented in the free, online Flora of North America, happily I know. It's the Hairy Maidenhair, ADIANTUM TRICHOLEPIS, of which the Flora of North America rather crisply states, "Sporulating late winter--early spring. Moist, shaded, limestone cliffs along streams and rivers, on boulders in creeks, and among rocks on steep slopes; 200--500 m; Tex.; Mexico; Central America in Guatemala, Belize."
Maindenhairs -- ferns of the genus Adiantum -- "sporulate," or produce spores, in a distinctive manner, as shown in the close-up below:
There you see three pinnules -- the smallest divisions of the compound fronds -- with curled-under, or "reflexed," margins. The reflexed margins serve as indusia, which in other species we've looked at gave the appearance of very thin, cellophane-like coverings over the sporangia. So, spores are being released from inside the pinnules' reflexed margins.
The picture also shows how Hairy Maidenhairs get the hair in their name. A similar maidenhair occurring over much of the same area and in similar habitats is hairless, or "glabrous."