Английская Википедия:Argyrochosma fendleri

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Шаблон:Short description Шаблон:Speciesbox Argyrochosma fendleri, Fendler's false cloak fern, is a fern known from the western United States and northwestern Mexico. It grows in rocky habitats, and is distinguished from other members of the genus by its zig-zag leaf axes. Like many species in the genus, it bears white powder on the underside of its leaves. First described as a species in 1851, it was transferred to the new genus Argyrochosma (the "false cloak ferns") in 1987, recognizing their distinctness from the "cloak ferns" (Notholaena sensu stricto).

Description

Argyrochosma fendleri is a medium-sized epipetric fern. The rhizome is compact, Шаблон:Convert wide, and may be horizontal or upright. It bears linear to lanceolate scales Шаблон:Convert long,Шаблон:Sfn thin in textureШаблон:Sfn and of a uniform orange-brownШаблон:Sfn or chestnut-brown colorШаблон:Sfn with entire (toothless) margins.Шаблон:Sfn

Numerous fronds arise in dense clumps from the rhizome.Шаблон:Sfn From base to tip of leaf, they are Шаблон:Convert longШаблон:SfnШаблон:Sfn and Шаблон:Convert wide.Шаблон:Sfn Of this length, about half is made up by the stipe (the stalk of the leaf, below the blade), which is round, hairless, and chestnut-brown in color. It typically measures from Шаблон:Convert in diameterШаблон:Sfn and Шаблон:Convert in length.Шаблон:Sfn

The leaf blades are deltate (triangular) in shape, highly divided (from four to six successive subdivisions) at the base,Шаблон:SfnШаблон:Sfn sometimes broader than they are long.Шаблон:Sfn They curl slightly upwards when dried.Шаблон:Sfn The rachis (leaf axis) is round, rather than flattened, hairless, and zig-zags rather than being straight.Шаблон:Sfn Each blade bears 4 to 6 pairs of pinnae, whose costae also zig-zag, with subdivisions branching off at the angles.Шаблон:SfnШаблон:Sfn The ultimate segments are ovate to lanceolateШаблон:Sfn or oblong,Шаблон:Sfn obtuse at the tip and broadly cuneate (wedge-shaped) at the base,Шаблон:Sfn and sometimes have an crenate (round-toothed) margin.Шаблон:Sfn The dark color of the axes passes into the segment base, without a distinct joint,Шаблон:SfnШаблон:Sfn and pinnae and subsequent subdivisions are borne on long stalks.Шаблон:Sfn The underside of the leaf is coated in pale white farina (powder), and a scattering of glands and farina is sometimes present on the upper surface.Шаблон:SfnШаблон:SfnШаблон:Sfn The leaf tissue is leathery to somewhat leafy in texture.Шаблон:Sfn

The sori lie along the veins, along the final quarter of the length of the veins closest to the edge of the leaf.Шаблон:Sfn The veins themselves tend to blend into the leaf tissue. The leaf edges are not modified into false indusia, and may be flat or curled under to cover the sori.Шаблон:SfnШаблон:Sfn Each sporangium bears 64 spores. The plants are diploid, with a chromosome number of 2n = 54.Шаблон:SfnШаблон:Sfn

The zig-zag rachis and axes generally serve to distinguish it from other members of the genus.Шаблон:Sfn A. limitanea may have slightly zig-zag axes, but its subdivisions are not as strongly spreading.Шаблон:Sfn Furthermore, A. limitanea is apogamous and only contains 32, rather than 64, spores per sporangium.Шаблон:Sfn

Taxonomy

The species was first described by Gustav Kunze in 1851 as Notholaena fendleri, based on material collected in New Mexico by Augustus Fendler, for whom it is named.Шаблон:Sfn Delineating natural genera in the cheilanthoids has proven to be extremely difficult, and other placements of the species were subsequently put forward. Fée transferred it to Cincinalis as Cincinalis fendleri in 1852, breaking with most other authorities in recognizing and re-circumscribing that genus.Шаблон:Sfn In 1859, Mettenius rejected Fée's attempt to delineate Cincinalis as a separate genus, but recognized the genus Gymnogramma for species where sporangia were borne along the nerves and not densely clustered at the end of the nerves.Шаблон:Sfn He transferred the species there as G. fendleri.Шаблон:Sfn Prantl expanded Pellaea to include several genera in which he perceived close affinities, including Cincinalis. Accordingly, he transferred C. fendleri to Pellaea section Cincinalis as P. fendleri in 1882.Шаблон:Sfn In 1979, John T. Mickel transferred it to Cheilanthes as Cheilanthes cancellata (the epithet fendleri was preoccupied), as part of an effort to create a more coherent Notholaena.Шаблон:Sfn

A highly-compound fern leaf of small gray-green leaflets connected by dark zig-zag axes, a few showing an underside covered in white powder
Argyrochosma fendleri leaf, showing the coating of white farina below and the characteristic zig-zag axes.

By the late 20th century, most authorities favored placement of Notholaena nivea and closely related ferns, including N. fendleri, either in Notholaena or Pellaea. Both Edwin Copeland and C. A. Weatherby suggested in the 1940s that this group of ferns might represent a distinct genus of its own.Шаблон:Sfn This was finally addressed in 1987 by Michael D. Windham, who was carrying out phylogenetic studies of these genera. He elevated Notholaena sect. Argyrochosma to become the genus Argyrochosma,Шаблон:Sfn and transferred this species to that genus as A. fendleri.Шаблон:Sfn In 2018, Maarten J. M. Christenhusz transferred the species to Hemionitis as H. engywookii (the epithet fendleri was preoccupied), as part of a program to consolidate the cheilanthoid ferns into that genus. The epithet refers to the gnome scientist Engywook in the novel The Neverending Story.Шаблон:Sfn

Phylogenetic studies have shown that A. fendleri forms an isolated clade, diverging at an early date from the other two clades of farina-bearing Argyrochosma.Шаблон:Sfn Its farina is chemically distinct from that of other Argyrochosma, consisting mostly of eriodictyol-7-methyl ether, a compound rare in ferns.Шаблон:Sfn

Distribution and habitat

Argyrochosma fendleri is known in the United States from New Mexico, Colorado, and the southeastern corner of Wyoming,Шаблон:Sfn and in Mexico from Sonora.Шаблон:Sfn

It grows on rocky cliffs and slopes, particularly on granitic and igneous rocks, the only member of the genus to prefer this substrate. It is found at an altitude from Шаблон:Convert.Шаблон:Sfn

Conservation

Under the NatureServe conservation status system, A. dealbata is ranked as vulnerable (G3), but it is considered critically imperiled in Wyoming and vulnerable in Colorado.Шаблон:Sfn

Cultivation

The horticulturist George Schneider considered it suitable for conservation, noting that it "thrives well under cool treatment",Шаблон:Sfn perhaps in contrast to tropical ferns.

Notes and references

References

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Works cited

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External links

Шаблон:Taxonbar

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