Excerpts from Jim Conrad's
from the November 22, 2009 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO
SOUTHERN LIP FERN
On old stone walls here built of limestone -- many of those stones surely once incorporated in ancient Maya temples -- several interesting fern species have found homes, such as the foot-high one shown above. A close-up showing the underside of a pinna is shown abelow:
The manner in which the pinna's margins curl under partially enclosing lines of spore-containing, sandgrain-like sporangia helps us identify this as a "lip fern" of the genus Cheilanthes. Lip ferns are typical of such dry, sunny spots as our stone walls and often are invested with stiff hairs just like ours. In The Flora of North America our wall-fern keys out to the Southern Lip Fern, CHEILANTHES MICROPHYLLA. Southern Lip Ferns are listed for the Yucatan, and our plants match drawings on the Internet, but I can't find good pictures on the Internet to cinch the ID. Word descriptions fit it perfectly, however, especially the way the black stem color extends a good way up the center of the pinna, as shown in the last photo. So, I'm about 95% sure of the ID, but there might be a local species very similar to the Southern Lip Fern I don't know about.
The Flora of North America describes the Southern Lip Fern's habitat as "calcareous rock outcrops and shell mounds," and our limestone walls are perfect calcareous rock outcrops. The species is distributed from the US Southeast south to South America, including the Caribbean, where it is most common.