Argyrochosma

Synonyms Cheilanthes, Notholaena, Pellaea Argyrochosma gathers together some 20 intriguing xeric species that until 1987 (Windham) were classified under one or another of the above synonyms. The appropriately descriptive genus name Argyrochosma, from the Greek argyros, silver, and chosma, powder, references the waxy, white protective foliar undercoat that decorates many of the species. Others are included by virtue of the stalks and cordate bases on the minute ultimate segments. These are plants, frequently with bluish pinnae, of the New World drylands and grow efficiently on or among rocks. In times of stress and dehydration, they will fold their pinnae to expose the waxy undersides, which will offer a bit of protection from heat and deter water loss.

Argyrochosma dealbata (whitened), synonyms Cheilanthes dealbata, Notholaena dealbata, and Pellaea dealbata, bears the consistent common name, powdery cloak fern. This miniature lime lover, native to the north-south corridor of the central United States, manages to split its 3- to 4-in. (7.5- to 10-cm) triangular blades into quadripinnate to quinquipinnate divisions of delicate finery. The undersides carry the signature coating of white farina, while the upper blade surface is dull and lacking in ornamentation. All of this diminutive foliar display is crowded atop proportionately tall, wiry stipes that are equal in length to the blade and grow from short-creeping rhizomes. This, like other members of the genus, is a plant for the grower who enjoys a challenge. It is cold tolerant in Zones 6 to 9, but needs a basic soil and is touchy about exposure (requires bright light) and drainage (must be immediate and efficient). It is so closely related to the equally difficult and beautiful border cloak fern, A. limitanea (bounded, limited) of the U.S. Southwest and Mexico, that they can be treated as equals in their specialized demands and garden requirements. The latter is apogamous.

A frond of Araiostegia pseudocystopteris retiring for the winter.
Argyrochosma dealbata nestles in rocks at the Roaring River State Park in Missouri.

Argyrochosma limitanea in the University of California Botanical Garden at Berkeley.

Argyrochosma fendleri (for August Fendler, 1813-1883, a German naturalist who plant collected in the U.S. Southwest and Central America), the zigzag cliff break or latticework cloak-fern, synonyms Notholaenafendleri, Cheilanthes cancel-lata, and Pellaea fendleri, has an open "latticework" structure of up to 12 in. (30 cm), carrying minute starry sprays of pinnules on zigzag stems. The under surfaces are protected from the elements with a white waxy coating. This is the only Argy-rochosma with a preference for acid soil and can be admired on the trails in New Mexico and Colorado. While it is not generally in cultivation, for potential garden use in Zones 5 to 8 give it good drainage in rough compost preferably amended with small, 1/2 in. (13 mm) or less, bark chips. Protection from winter wet is mandatory.

Argyrochosma jonesii (after Jones), Jones' cloak fern, is a rarely cultivated delicacy from limestone sites in the U.S. Southwest and adjacent regions in Mexico. The stipes are dark and the lanceolate blades are bipinnate to tripinnate with pinnae and pinnules supported by dark stalks. It does not share the characteristic white waxy undercoat that typifies the genus. It can be cultivated with the utmost care by California xeric specialists in coarse, well-drained but moist limestone grit. It will survive in Zones 8 and 9 cold, but prefers a summer rather than winter rainy season.

Argyrochosma microphylla (small leaves, a name that could be applied to the entire genus) lacks a white petticoat, but shares the typical display of minute dusky pinnae. Tripinnate to quadripinnate ovate blades are carried on dark stipes with the whole ranging from 5 to 10 in. (13 to 25 cm) in height. This native of limited limestone sites on both sides of the U.S.-Mexican border is an attractive addition to pot culture collections or, for the truly committed, a customized site in desertlike Zone 8 to 9 garden surroundings. Wet winter habitats are not suitable.

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