Английская Википедия:Argyrochosma formosa

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Шаблон:Short description Шаблон:Speciesbox Argyrochosma formosa is a fern known from eastern and central Mexico and Guatemala. It grows on rocky slopes, particularly on limestone. Unlike many members of the genus, it lacks white powder on the underside of its leaves. First described as a species in 1842, 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 formosa is a medium-sized epipetric fern. The rhizome is compact and horizontal.Шаблон:Sfn It bears linear scales Шаблон:ConvertШаблон:Sfn or Шаблон:Convert long and Шаблон:Convert wide,Шаблон:Sfn hair-tippedШаблон:Sfn and with entire (toothless) margins.Шаблон:Sfn They range from tan to dark orangeШаблон:Sfn or rusty in colorШаблон:Sfn and feel oily-viscid.Шаблон:Sfn

The fronds arise in clumps from the rhizome. They are from about Шаблон:Convert long,Шаблон:SfnШаблон:Sfn sometimes as short as Шаблон:Convert, and Шаблон:Convert broad.Шаблон:Sfn Of their length, about 25% to 50% is made up by the stipe (the stalk of the leaf, below the blade), which is shiny or sometimes glaucous and round, hairless, and reddish-brown to dark purple or black in color.Шаблон:SfnШаблон:Sfn The rhizome scales may continue to the base of the stipe.Шаблон:SfnШаблон:Sfn

The leaf blades are tripinnate to quadripinnate (cut into pinnae, pinnules and pinnulets, those sometimes fully cut) and range in shape from ovate to long-deltate (triangular) to ovate-lanceolate.Шаблон:SfnШаблон:Sfn The rachis (leaf axis) is round, rather than flattened.Шаблон:Sfn The rachis and the axes of the leaf segments are all dark in color; the color stops abruptly at a joint at the base of the leaf segment.Шаблон:Sfn Each blade bears 6 to 9 pairs of pinnae, borne alternately or nearly oppositely on the rachis,Шаблон:Sfn with an acute (pointed) tip.Шаблон:Sfn The ultimate segments of the blade are orbicular (circular) or inequilaterally cordate (asymmetrically heart-shaped), Шаблон:Convert long,Шаблон:Sfn sometimes to Шаблон:Convert.Шаблон:Sfn They are borne on short stalks.Шаблон:Sfn The underside of the leaf lacks the farina (powder) that characterizes many members of the genus,Шаблон:Sfn although both upper and lower surfaces of the leaf are usually glaucous.Шаблон:Sfn

The sori lie along the veins, forming a band Шаблон:Convert wideШаблон:Sfn on the outermost quarter of the vein.Шаблон:Sfn The leaf edges are curved under,Шаблон:Sfn sometimes to the point of touching one another,Шаблон:Sfn but otherwise not modified into false indusia. Fertile segments often fold along their long axis, giving them a sagittate (arrowhead-like) shape. Specimens from Oaxaca were found to be apomictic triploids, with a chromosome number of n = 2n = 81.Шаблон:Sfn

While it is similar in overall appearance to A. incana, it is easily distinguished from that species by its lack of farina. In Mexico, the only other member of the genus to lack farina is A. microphylla, which has smaller leaf segments, chestnut-brown, rather than black, leaf axes,Шаблон:Sfn a grooved rachis and dry rhizome scales.Шаблон:Sfn

Taxonomy

The species was first described in 1842 as Allosorus pulchellus by Martin Martens & Henri Guillaume Galeotti, based on material collected by Galeotti in Mexico.Шаблон:Sfn The epithet pulchellus means "small and beautiful"Шаблон:Sfn and presumably reflects the aesthetic appeal of the species, which they described as "charmante".Шаблон:Sfn However, that name had already been used in 1836 for a different species, the former Cheilanthes pulchella, by Carl Borivoj Presl, rendering it nomenclaturally illegitimate. Frederik Liebmann recognized the issue and corrected it by giving Martens & Galeotti's species the replacement name Allosorus formosus in 1849;Шаблон:Sfn the epithet formosus means "beautiful".Шаблон:Sfn

Delineating natural genera in the cheilanthoids has proven to be extremely difficult, and other placements of the species were subsequently put forward, mostly as replacement names for A. pulchellus in other genera using the same epithet. Fée transferred it to Pellaea as Pellaea pulchella in 1852.Шаблон:Sfn In 1857, Thomas Moore, in his Index Filicum, transferred it to Platyloma, a genus he recognized as a segregate from Pellaea, as Platyloma pulchellum.Шаблон:Sfn John Smith, in 1866, preferred to recognize a different cheilanthoid segregate, Cincinalis, and placed it there as Cincinalis pulchella.Шаблон:Sfn In 1922, William Ralph Maxon created a new combination for Liebmann's name in Pellaea, as Pellaea formosa due to the illegitimacy of Martens & Galeotti's name,Шаблон:Sfn although subsequent changes to the practice of nomenclature would make it superfluous. Oliver Atkins Farwell, following a program of reviving what he considered to be senior synonyms, gave Cassebeera priority over Pellaea and transferred the species there as Cassebeera pulchella in 1931.Шаблон:Sfn

Maxon and Charles Alfred Weatherby placed Pellaea formosa within a group of ferns closely related to Notholaena nivea, but declined to make a nomenclatural transfer until the classification of the cheilanthoids was better understood.Шаблон:Sfn Both Edwin Copeland and 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. formosa.Шаблон:Sfn Meanwhile, John Mickel and Joe Beitel had transferred the species to Cheilanthes as C. formosa in their monograph on the ferns of Oaxaca, which was published in 1988;Шаблон:Sfn Mickel and Alan R. Smith recognized Argyrochosma in 2004 when preparing a fern flora of Mexico.Шаблон:Sfn In 2018, Maarten J. M. Christenhusz transferred the species to Hemionitis as H. formosa, as part of a program to consolidate the cheilanthoid ferns into that genus.Шаблон:Sfn

underside of fern frond divided into cordate segments connected by black axes, the black color passing into the base, spores visible but no white powder
Argyrochosma formosa, showing lack of farina and dark color of axes passing into leaf segments

Phylogenetic studies have shown that A. formosa is a sister species to A. microphylla; these two species form a clade sister to another clade containing A. jonesii and A. lumholtzii.Шаблон:Sfn All four species lack farina, and their common ancestor is hypothesized to have diverged from the ancestor of the rest of the genus before farina production developed in the latter.Шаблон:Sfn

Distribution and habitat

Argyrochosma formosa is distributed from the northernmost provinces of Mexico through eastern and central Mexico to Chiapas and into Guatemala.Шаблон:Sfn

In Mexico, it grows on dry rocky slopes and in ravines, often on limestone, as well as in thorny scrub. It has been found growing in mortar at Monte Albán.Шаблон:Sfn Most common in similar habitats in Guatemala, it also occurs on hillsides and riverbanks, and in forests and thickets.Шаблон:Sfn It is found at an altitude from Шаблон:Convert.Шаблон:Sfn

Notes and references

References

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Works cited

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