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Excerpts from Jim Conrad's
Naturalist Newsletter
entry from field notes dated June 28, 2022, taken in oak forest on slopes of Cerro de la Cruz, elevation ~2750m (~9000 ft), rising on the south side of the community of El Pinar, Amealco de Bonfil, Querétaro, MÉXICO, (~N20.17°, ~W100.17°)
BLACK-STEMMED SPLEENWORT
The above yellowing fronds surviving from the last rainy season emerged from a tangle of dry oak leaves and old vine stems covering a crust of mosses and lichens. The mess covered an old north-facing roadcut through dirt derived from volcanic rhyolite bedrock. The fronds' undersurfaces were still releasing spores, the sori formed of masses of granular sporangia as shown below:
With the fronds' blackish stems, or rachises, and the general form of the leaflets, or pinnae, and the sori, this was a typical species of the big, commonly occurring group of ferns known as spleenworts, genus Asplenium. With about 700 spleenwort species recognized worldwide, of which 28 occur in North America, 88 in Mexico, and 22 just in our upland, semi-arid region of central Mexico known as the Bajío, when you see a spleenwort, it's a good idea to pay close attention, because it may be a challenge to figure out the species.
In this case, I already knew the species, or a very similar one, from my days in the southeastern US: the Black-stemmed Spleenwort, Asplenium resiliens. That species occurs spottily across the US Southeast and south-central regions, and the Caribbean area, south through Mexico into Guatemala, then also in much of South America, to Argentina and Brazil.
However, I've always thought of this as a species of limestone areas, and limestone neutralizes a soil's natural acidity, while the bedrock here was volcanic rhyolite, which tends to produce acidic soils. Also, the shallow indentations on the pinnae margins of our fern are a little more sharply pointed than I'm accustomed to.
Still, in the authoritative Flora del Bajío our fern "keys out" as ASPLENIUM RESILIENS, plus the species is known to hybridize with other species, and any species occurring over such a large area, especially so spottily, is likely to show local variations. Moreover, the 2012 gene study by Robert J. Dyer and others entitled "Apomixis and reticulate evolution in the Asplenium monanthes fern complex" found that the A. resiliens "clade" consisted of three lineages, plus our fern was confirmed to be apomictic, meaning that it reproduces asexually. And I can't find any other species occurring in the area it might be. So, keeping in mind that a world of variables exist and Nature makes no effort to fit Her organisms into humanity's pigeonholes, Asplenium resiliens is how we'll file it here.
That name "spleenwort" is from the Greek splen, for spleen, and wort is a general Latin word for plant, herb, vegetable, etc. The spleenwort name comes about because Dioscorides thought that this group of ferns was useful for treating spleen diseases. Dioscorides was a Greek physician and botanist who authored a five-volume encyclopedia of herbal medicine, De materia medica, which Western doctors consulted for centuries.