Excerpts from Jim Conrad's
Naturalist Newsletter

from the April 9, 2017 Newsletter, a special on-the-road edition with notes from Micos Cascades on the Río Salto maybe 30kms northwest of Ciudad Valles in the state of San Luis Potosí, MÉXICO

Last week, travelling by bus up through Mexico to Kentucky, at Micos Cascades on the Río Salto maybe 30kms northwest of Ciudad Valles in the Mexican state of San Luis Potosí, a certain fern caught my attention. It was fairly common on limestone rock and hard-packed mud right at the rushing water's edge. One fern about two feet across (70cm) is shown below:


You can see that the fern's leathery fronds are pinnately compound, and that the leaflets, or pinnae, display wavy to slightly toothed margins. The fronds' stems, at least toward their bases, are blackish. This fern species definitely is not a frilly looking or delicate one. In fact, I wasn't absolutely sure that it was even a fern until I flipped over a frond and saw widely spaced, round, spore-producing fruit-dots, or "sori," shown below:

Japanese Holly Fern, CYRTOMIUM FALCATUM, sori

Those sori are worth examening, as you can see up close below:

Japanese Holly Fern, CYRTOMIUM FALCATUM, sori close-up

In most fern species with sori on the fronds' undersurfaces, the sori are long or, if they're roundish, they don't look like this. In the above picture, the doughnut-shaped sori are composed of two main parts. First, there's the pale-yellowish-green, ring-shaped "indusium." Most sori indusia are long, thin flaps of tissue with one side attached to the blade while the other side opens so that those tiny, brown, seed-like things can emerge from the resulting slit. Here the indusia are circular and attached at their center -- they're "peltate." That's really interesting. The tiny, brown things along the margins are stalked, baglike sporangia, with each sporangium containing several dust-like spores. When the sporangia are mature they burst, release their spores into the wind, and the spores will be carried to a new location where, if environmental conditions are just right, they'll germinate. To get all these terms better fixed in your mind you may want to look at our Fern Page at http://www.backyardnature.net/ferns.htm.

Our pictures show the Japanese Holly Fern, CYRTOMIUM FALCATUM, native to eastern Asia, but in the wild growing from rock crevices, on coastal cliffs, streambanks, rocky slopes -- all in fairly moist places. It's on a streambank in Mexico, as well as similar environments in most of the rest of the tropical and subtropical world, because it's become a popular ornamental plant that sometimes escapes into the wild. Apparently the plants I found were either just getting established, or not in an environment entirely to their liking, because pictures of the species on the Internet show larger plants with fronds divided into more numerous pinnae. The Flora of North America says the pinnae can arise in up to twelve pairs, and that the fronds can reach over a meter in length (over three feet). The Flora also describes the species as "apogamous," meaning that its embryo can develop without fertilization having taken place -- which might be one reason this fern species has become so weedy.