Argyrochosma

Argyrochosma
Argyrochosma jonesii
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Order: Polypodiales
Family: Pteridaceae
Subfamily: Cheilanthoideae
Genus:
(J.Sm.) Windham
Type species
Pteris nivea
Species

See text.

Argyrochosma is a genus of ferns known commonly as false cloak ferns. The genus is included in the Cheilanthoideae subfamily of the Pteridaceae.[1] Species now in this genus were previously treated as members of related genera Notholaena or Pellaea but were segregated into their own genus in 1987.

Description

The fronds of Argyrochosma species are generally shorter than 40 cm (16 in) and have rounded bluish or grayish green segments. Often the lower surface of the segments is coated in a white dust, and the sporangia contain brown spores.

Taxonomy

The group of species comprising the genus was first described by John Smith in 1842 as Notholaena sect. Argyrochosma. He included in the genus species with a variety of coverings on the undersurface of the leaf, and assigned to this section those that were covered in white farina.[2] Smith's name is derived from the Greek words ἄργυρος (argyros), "silver" and χῶσμα (chosma), "mound of earth".[3][a] Carl Christensen considered the section to be more properly classified in Pellaea, and designated Pellaea nivea as the lectotype for it.[5]

By the late 20th century, most authorities favored placement of a group of ferns, exemplified by Notholaena nivea, either in Notholaena or Pellaea. Both Edwin Copeland and C. A. Weatherby suggested in the 1940s that the group might represent a distinct genus of its own.[6] In 1948, Weatherby advised Conrad Vernon Morton, preparing some treatments of American ferns, that these species, including some similar to N. nivea but without farina, were better placed as a section of Pellaea than in Notholaena. In the following year, he advised Morton that "this is one of the two groups (and the better of the two) which I can see clearly as a segregate genus...which...should bear the name Argyrochosma (J. Smith). I may live to publish on this."[7] He did not, and so the task was 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 and made suitable combinations for the recognized species.[8] Two varieties of Argyrochosma nivea were transferred to the new genus in 1996 by M. Mónica Ponce,[9] and subsequently elevated to species level in the genus in 2017 by Michael Kessler and Alan R. Smith.[10] Meanwhile, in 2015, Gangmin Zhang and co-workers identified Argyrochosma connectens, a rare Chinese species formerly placed in Pellaea, as a member of the genus by DNA analysis.[11]

Members of the genus Argyrochosma are commonly known as false cloak ferns or silver ferns.[12] "False cloak fern" refers to the historical placement of these species in the genus Notholaena. The name of that genus is derived from Greek, meaning "false cloak", referring to the fact that the sori are not covered by well-differentiated tissue of the leaf margin, and its species were commonly known as "cloak ferns".[13] "Silver fern" is evidently derived from the name Argyrochosma, which means "silver mound" and refers to the white farina found on the underside of the leaves of most species.[3]

Species

As of July 2025, the Checklist of Ferns and Lycophytes of the World recognized the following nineteen species:[14]

Distribution and habitat

These ferns are mostly native to the Americas, from North to South and including the Caribbean, while one species, A. connectens, is known from Sichuan, China.[15] They are commonly found growing in crevices of rocks.

Notes

  1. ^ Sometimes freely translated as "powder",[4], although Smith's original division of Notholaena into sections Argyrochosma, Eriochosma and Lepichosma depending on whether white farina, tomentose hairs, or scales covered the underside[2] suggests an emphasis on the heaping of material.

References

  1. ^ Christenhusz, Maarten J. M.; Zhang, Xian-Chun; Schneider, Harald (18 February 2011). "A linear sequence of extant families and genera of lycophytes and ferns" (PDF). Phytotaxa. 19 (1): 7–54. Bibcode:2011Phytx..19....7C. doi:10.11646/phytotaxa.19.1.2. ISSN 1179-3163.
  2. ^ a b Smith 1842, p. 50.
  3. ^ a b Quattrocchi 2000, p. 193.
  4. ^ Windham 1993.
  5. ^ Christensen 1906, p. XL.
  6. ^ Windham 1987, p. 37.
  7. ^ Morton 1950, pp. 249–250.
  8. ^ Windham 1987, p. 38.
  9. ^ Ponce 1996, p. 177.
  10. ^ Kessler, Smith & Prado 2017, p. 206.
  11. ^ Wang et al. 2015, p. 37.
  12. ^ Diggs & Lipscomb 2014, p. 213.
  13. ^ Clute 1901, pp. 287.
  14. ^ Hassler, Michael. "Argyrochosma". World Ferns. Retrieved 2025-07-15.
  15. ^ Wang et al. 2015, p. 30.

Sources

Further reading

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