Argyrochosma dealbata

While running transects across the grassy ledges and shelves of Hercules Glades Wilderness in Taney County Missouri, I paused to wipe the accumulation of sweat and juniper needles from my brow. As my heart rate approached conditionally normal, given the heat, my eyes focused on a tiny patch of bluish vegetation clinging to the otherwise salt and pepper fa├žade of the sun and lichen aged limestone rock; the jutting and ever dissolving bones of the Ozarks. I leaned in.

Puzzled, I looked around the ledge and discovered eight more small clumps of this little fern. I am accustomed to seen Cheilanthes feei on such rocks in such habitat, but this was strikingly different. In fact, Chelanthes feei was growing on the same ledge some 24 inches away and made for apt comparison. Hot blood squeezed through my brain and I was surprised when the name Notholaena dealbata surfaced; a fern I had only seen on glades along the Blue River in Kansas City. A quick cruise through several cold blooded references verified the identification.

Notholaena dealbata (Powdery Cloak Fern) is currently referred to as Argyrochosma dealbata on the USDA PLANTS website. Taxonomically, it seems to fit somewhere between the genus Cheilanthes and Pellea. I can certainly see the similarity with the latter. The core of its range extends from eastern Kansas and southwest Missouri into Oklahoma, Arkansas and Texas with outlying populations in Illinois, Kentucky and Nebraska. It only occurs on outcrops of calcareous rock.

The sweetest thing about Argyrochosma dealbata is not the blue coloration or the revolute margins of the pinnae, but the farina of the abaxial surfaces of the pinnae (the white color in the photo below is the farina).

The farina, in this case, is a waxy exudate. I can only speculate as to its function, but won’t. The dark spheres are sporangia each containing 64 spores. Morphologically, the genus Argyrochosma differs from Cheilanthes and Pellea in the possession of farina and was split from Notholaena based on a different chromosome number (n=27). Argyrochosma means “silver powder” in reference to the farina.

I have always been enamored with small ferns. This is probably my favorite, for obvious reasons.

Comments

  1. That's a pretty cool fern you've found there, Justin. I'd never heard of such a thing. Nice work.

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  2. That is so cool, Justin. I am in Marquette right now doing rare plant surveys and am awash in ferns, at least relative to what I see in the rock-starved southern Lower Peninsula.

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  3. I love it!!!!!! Finding such an unusual rarity would be the high point of an entire year for me.
    Thoreau said, "Nature made ferns for pure leaves, to show what she could do in that line."

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