A "Filmy Fern" in the Genus Cystopteris

Abstract

The northwestern part of the Mexican state of Oaxaca along the border with Puebla is relatively poorly collected botanically. Much of the area between Huajuapan de Leon, Oax., and Tehuacan, Pue. is extremely dry semidesert. A dry valley extends from Tehuacan to Teotitlan del Camino in Oaxaca. From the latter city there is a road to the northeast that goes over the mountains to the village of Huautla de Jimenez. This road has been best known in recent years for its halucinogenic fungi, hippies, and police-in that order. The road rises steeply out of Teotitlan and snakes its way up to the top of a ridge, crossing it at Puerto Soledad. The upper parts of the slope are forested with pine and oak. The forest at the top is the wettest and consists largely of oaks and some Podocarpus. The wet winds from the Gulf of Mexico keep this region moist the year around. I have collected over 100 species of ferns within two miles of the pass, where the wet forest is nearly continuous. The road continues near the top of the ridge, dives to the bottom of another valley and climbs part of another ridge before reaching Huautla de Jimenez. Most of the road is heavily cultivated or at least cut over. After passing Puerto Soledad, which is 19 miles by road from Teotitlan, the forest is soon interrupted by agriculture, but there are small patches of forest and several waterfalls by the road. In 1970 Mr. Steven Leonard and I collected a remarkably filmy fern on the ground in the spray beside a small waterfall. At first it looked to us somewhat like Trichomanes radicans, for its leaf tissue was only one or two cells thick. But on closer examination I found that the plant had tiny dorsal sori with hood-like indusia typical of Cystopteris. A similar specimen was found at the United States National Herbarium from Veracruz, also from a waterfall. This suggests that the thin frond texture may be due to constant waterfall spray, but apparently this is not the case. A plant was grown for nearly a year in the greenhouse of the New York Botanical Garden, during which time the new leaves continued to be as filmy as those of the original plant. Consequently, I am describing the plant as a new species: