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Excerpts from Jim Conrad's
Naturalist Newsletter
entry dated March 15, 2022, issued from near Tequisquiapan, elevation about 1,900m (6200 ft), ~N20.57°, ~ W99.89°, Querétaro state, MÉXICO
HYBRID CLOAKFERN
As these advanced-dry-season days grow warmer and the landscape becomes ever more parched, dusty and brown-and-gray, the above fern sprouting from the side of rocky ledge is so brittle that it breaks like glass if handled too roughly. The cliff exhibits a geology typical of this area. It's a kind of soft rock, or rock-like compacted dirt, locally called tepetate, composed of an ancient deposition of mingled volcanic ash and sediment from surrounding hills mostly constituted of rhyolite. Up close the fern's pinnae show distinctive features for this species:
The fronds are so heavily invested in large, silvery, branching and unbranching scales that the plant's surface is hard to see. The picture shows two piannae on a frond. The pinna at the left arises on the frond rachis's far side, so we see the pinna's upper surface. The pinna at the left, arising on the near side, display's its woolly underside. The pinnae's upper sides aren't nearly as woolly as the undersides. On the pinna underside at the right, at least one tiny, brown, spherical, spore-producing sporangium is visible, at the far right, inside the pinna.
The pinnae's small size, about 10mm, and their oval to roundish shape, with hardly any hint of lobes forming, also distinguish this species, helping making it relatively easy to identify. Its English name often is given as Hybrid Cloakfern, the name Cloakfern being used for species of the genus Astrolepis. This is ASTROLEPIS INTEGERRIMA, fairly commonly noticed on deserty, rocky hillsides and cliffs from Arizona to Oklahoma and Texas south into our area in central Mexico. It especially favors limestone areas, though our populations show that it can appear on other substrates as well.
The "Hybrid" part of its name comes from its being a "polyploid" species, meaning that in its cell nuclei three or more sets of chromosomes coexist, having been derived from at least two different species. Normally different species can't reproduce with one another, but polyploids with three or more chromosome sets is common among ferns, with over 95% of fern species being so. However, our Hybrid Cloakfern has been shown to have arisen from a minimum of ten preexisting species. You may be interested in a freely accessible, 1999 online paper by James Beck and others, entitled Identifying multiple origins of polyploid taxa: a multilocus study of the hybrid cloak fern (Astrolepis integerrima; Pteridaceae).
In general, Hybrid Cloakferns in the US have somewhat larger pinnae than ours, and they normally display asymmetrical, shallow lobes.
entry dated June 21, 2022, issued from near Tequisquiapan, elevation about 1,900m (6200 ft), N20.565°, W99.890°, Querétaro state, MÉXICO
The rainy season came late this year. After a shower, the Hybrid Cloakferns expanded to look more fernlike:
Scales on the pinnae's undersurfaces are even more impressive now:
