Argyrochosma chilensis

Argyrochosma chilensis is a fern endemic to the Juan Fernández Islands off the coast of Chile. It has leathery, thrice-divided leaves with dark brown axes; the leaves are coated with white powder below. First described as a species in 1853, it was transferred to the new genus Argyrochosma (the "false cloak ferns") in 1987, recognizing their distinctness from the "cloak ferns" (Notholaena sensu stricto).

Argyrochosma chilensis
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Class: Polypodiopsida
Order: Polypodiales
Family: Pteridaceae
Genus: Argyrochosma
Species:
A. chilensis
Binomial name
Argyrochosma chilensis
(Fée ex J. Rémy) Windham
Synonyms
  • Cincinalis chilensis Fée ex J. Rémy
  • Hemionitis chilensis (Fée ex J. Rémy) Christenh.
  • Notholaena chilensis (Fée ex J. Rémy) J.W.Sturm
  • Pellaea chilensis (Fée ex J. Rémy) C.Chr.

Description

Argyrochosma chilensis is a small epipetric fern. The rhizome is stout and upright. It bears thin, linear scales 3 millimeters (0.1 in) that terminate in a hair attached by a joint, of a bright brown color, without teeth at the margins.[1] From it, the fronds arise in clumps. From base to tip of leaf, they are 5 to 15 centimeters (2.0 to 5.9 in) long.[1] Of this length, about half is made up by the stipe (the stalk of the leaf, below the blade), which is round, a dark chestnut brown in color, and lacks scales and hairs.[1]

The leaf blades are roughly oval in shape, broadest at the lowest or second pair of pinnae, with an acute tip. They are tripinnate (cut into pinnae, pinnules, and pinnulets), typically bearing about five pairs of pinnae. The texture of the blade is leathery; the underside is densely covered in white farina (powder), which is absent from the upper side.[1] The pinnae are oval to lance-shaped, attached to the rachis (leaf axis) by short stalks. Each pinna is tipped with a three-lobed, diamond-shaped terminal pinnule; the other pinnules are cut into pinnulets, which are oblong, blunt at the tip, and generally lack stalks connecting them to the costule (pinnule axis). They are not jointed at the base.[1]

The sori lie along the veins, in the one-third to one-fourth of the vein closest to the leaf edge. The leaf edges are curved under, but not otherwise modified into false indusia. Each sporangium contains 64 spores.[1] The spores are covered with a network of raised crests, although portions of the surface lack elevated crests.[2]

Taxonomy

The first scientist to mention the species was Antoine Laurent Apollinaire Fée in 1852, who referred to it as Pellaea chilensis without offering a species description (making that name a nomen nudum), but noted that Jules Rémy, who was preparing a flora of Chile, considered it to belong to Lindsaea, in the sense used by Desvaux.[3] Rémy published his flora the following year, in the sixth botanical volume of Claude Gay's Historia fisica y politica de Chile, and described the species as Cincinalis chilensis, attributing that name to Fée.[4] In 1858, Johann Wilhelm Sturm transferred it into a broadly-construed genus Notholaena as N. chilensis.[5][lower-alpha 1] Carl Christensen, by contrast, assigned it to Pellaea as P. chilensis in his Index Filicum of 1906.[6]

While Rolla M. Tryon Jr., when finishing Charles Alfred Weatherby's revision of American Notholaena, considered it impossible to reasonably subdivide Notholaena into sections based on the data available at the time,[7] both Edwin Copeland and Weatherby himself had suggested in the 1940s that a group of ferns related to N. nivea might represent a distinct genus.[8] 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,[9] and transferred this species to that genus as A. chilensis.[10] In 2018, Maarten J. M. Christenhusz transferred the species to Hemionitis as H. chilensis, as part of a program to consolidate the cheilanthoid ferns into that genus.[11]

A phylogenetic analysis including a single specimen of A. chilensis found it nested within a clade representing A. nivea sensu lato.[12]

Distribution and habitat

Argyrochosma chilensis is endemic to the Juan Fernández Islands, particularly Robinson Crusoe Island and Alejandro Selkirk Island.[1]

It is found on rocks in dry, exposed situations, at altitudes from 20 to 40 meters (70 to 100 ft).[1]

Cultivation

The horticulturist George Schneider considered the species suitable for greenhouse cultivation.[13]

Notes
  1. Widespread homoplasy has made the delimitation of genera in the cheilanthoids based on morphology extremely difficult, and scientists have frequently disagreed on the placement of species such as this.

Citations
  1. Tryon & Weatherby 1956, p. 81.
  2. Morbelli et al. 2001.
  3. Fée 1852, p. 129.
  4. Gay 1853, p. 497.
  5. Sturm 1858, p. 166.
  6. Christensen 1906, p. 479.
  7. Tryon & Weatherby 1956, p. 6.
  8. Windham 1987, p. 37.
  9. Windham 1987, p. 38.
  10. Windham 1987, p. 40.
  11. Christenhusz, Fay & Byng, p. 11.
  12. Sigel et al. 2011, p. 562.
  13. Schneider 1892, p. 605.

Bibliography
  • Christenhusz, Maarten J. M.; Fay, Michael F.; Byng, James W. Plant Gateway's the Global Flora: A practical flora to vascular plant species of the world. 4. ISBN 978-0-9929993-9-1.
  • Christensen, Carl (1906). Index Filicum. Fascicles 1-12. Copenhagen: H. Hagerup.
  • Fée, A. L. A. (1852). "Genera filicum. Polypodiacées". Mémoires de la Société du muséum d'histoire naturelle de Strasbourg. 5.
  • Gay, Claude (1853). Historia fisica y politica de Chile. Botanica v. 6. Paris: E. Thunot & Co.
  • Morbelli, Marta A.; Ponce, M. Mónica; MacLuf, C. Cecilia; Piñeiro, María R. (2001). "Palynology of South American Argyrochosma and Notholaena (Pteridaceae) species". Grana. 40 (6): 280–291. doi:10.1080/00173130152987517.
  • Schneider, George (1892). The book of choice ferns for the garden, conservatory and stove. 2. London: L. Upcott Gill.
  • Sigel, Erin M.; Windham, Michael D.; Huiet, Layne; Yatskievych, George; Pryer, Kathleen M. (2011). "Species Relationships and Farina Evolution in the Cheilanthoid Fern Genus Argyrochosma (Pteridaceae)". Systematic Botany. 36 (3): 554–564. doi:10.1600/036364411X583547. JSTOR 23028975.
  • Sturm, J. W. (1858). "Enumeratio plantarum vascularum cryptogamicarum Chilensium". Abhandlungen der Naturhistorishcen Gesellschaft zur Nürnberg. 2: 151–202.
  • Tryon, Rolla M.; Weatherby, Una F. (1956). "A revision of the American species of Notholaena". Contributions from the Gray Herbarium of Harvard University (179): 1–106. JSTOR 41764632.
  • Windham, Michael D. (1987). "Argyrochosma, a new genus of cheilanthoid ferns". American Fern Journal. 77 (2): 37–41. doi:10.2307/1547438. JSTOR 1547438.
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