Argyrochosma limitanea

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Argyrochosma limitanea
Southwestern False Cloak Fern (38373216052).jpg
Fronds of southwestern false cloak fern growing from a rocky niche
Status TNC G4.svg
Apparently Secure  (NatureServe) [1]
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Order: Polypodiales
Family: Pteridaceae
Genus: Argyrochosma
Species:
A. limitanea
Binomial name
Argyrochosma limitanea
Subspecies
  • Argyrochosma limitanea subsp. limitanea
  • Argyrochosma limitanea subsp. mexicana(Maxon) Windham
Synonyms
  • Cheilanthes limitanea(Maxon) Mickel
  • Hemionitis limitanea(Maxon) Christenh.
  • Notholaena limitaneaMaxon
  • Pellaea limitanea(Maxon) C.V.Morton

Argyrochosma limitanea, the southwestern false cloak fern, is a species of fern native to the southwestern United States and Sonora, Mexico. It grows on calcareous rocks, and has small, finely-divided leaves with a leathery texture, dark axes connecting the leaf segments, and a heavy coating of white powder on the undersurface. It reproduces apogamously; two subspecies are recognized, which may have originated independently through the hybridization of other taxa not yet discovered. First described as a species in 1919, it was transferred to the new genus Argyrochosma (the "false cloak ferns") in 1987, recognizing their distinctness from the "cloak ferns" ( Notholaena sensu stricto ).

Contents

Description

The rhizome is short and horizontal, with leaves closely spaced. [2] It bears thin [3] linear to lanceolate [4] brown [2] [5] to reddish-brown [4] or chestnut-brown [3] scales, of a uniform color and with entire (toothless) margins. [3] [4]

The leaves range from 5 to 30 centimeters (2.0 to 12 in) long. [2] [5] The stipe (the stalk of the leaf, below the blade) is reddish-brown to black, rounded, without hairs or scales, [3] [6] [5] except that a few scales like those of the rhizome may be present at the very base. [3] It is 3 to 12 centimeters (1.2 to 4.7 in) long [4] and 0.75 to 2 millimeters (0.030 to 0.079 in) in diameter, [5] making up about one-half to one-third of the total length of the leaf. [2]

The leaf blades are 2.5 to 11 centimeters (0.98 to 4.3 in) long. [4] They vary from narrowly to broadly deltate (triangular) in shape, [7] [5] and ranges from tripinnate (cut into pinnae, pinnules and pinnulets) to pentapinnate at the base, where it is most divided. [7] [5] The rachis (leaf axis) is rounded or slightly flattened and hairless above, straight or slightly zig-zagging, [7] [5] and dark in color, as are the axes of the leaf segments. The color continues into the base of the leaf segments, without a distinct joint. [7] [5] From 6 to 12 pairs of pinnae are present, gradually narrowing at their tips and generally widest at their bases. [3] Leaf segments are numerous and closely spaced, small, [3] elliptic to ovate [4] or roundish to oblong in shape. [3] The leaf tissue has a leathery texture, obscuring the veins from the upper surface, and does not bear hairs or scales on either surface. The underside of the leaf has a thick covering of white farina (powder). [7] [5] [4] The leaves and axes curl upward when dry. [4]

In fertile leaf segments, the sporangia are close to the margin, borne along the further half of the secondary veins branching from the midrib of the segment. Each sporangium contains 32 spores. The leaf segments are curled under, often concealing the sporangia. [7] [5] A. limitanea is an apogamous triploid, with a chromosome count of n = 2n = 81. [7] [5]

Two subspecies are recognized: the typical A. limiteana subsp. limiteana, and A. limiteana subsp. mexicana. A. limiteana subsp. limiteana has broader blades (2 to 6 centimeters (0.8 to 2 in)), [4] broadly deltate-ovate in shape and more highly (4 to 5 times) divided at the base, with the lowest pinnae at least half the length of the entire leaf blade. [3] [5] [7] A. limiteana subsp. limiteana has narrower blades (1 to 2.5 centimeters (0.39 to 0.98 in)), [4] lanceolate to oblong in shape and less highly (3 to 4 times) divided at the base, with the lowest pinnae from one-third to one-quarter the length of the entire leaf blade. [3] [5] [7]

A. limitanea can be distinguished from A. incana and A. delicatula by its lack of a joint at the bases of leaf segments, with the dark color of the axes passing into the segment bases. [7] It is larger in all particulars than the closely related A. dealbata , [8] with darker leaf axes and thicker leaf tissue. [5]

Taxonomy

Argyrochosma limitanea leaf blade, showing white farina and dark color passing into leaf segments. Argyrochosma limitanea leaf underside.jpg
Argyrochosma limitanea leaf blade, showing white farina and dark color passing into leaf segments.

The species was first described in 1919 as Notholaena limitanea by William Ralph Maxon. The epithet limitanea presumably refers to its distribution along the border between the United States and Mexico; Maxon referred to it as the "Mexican Border plant" in distinguishing it from similar species. [9] He also described N. limitanea subsp. mexicana, with narrower leaves and some other characters distinguishing it from typical material. [10] Oliver Atkins Farwell lumped the latter into a broadly defined Notholaena nivea in 1931 as N. nivea var. mexicana. [11]

Both Edwin Copeland and Charles Alfred Weatherby suggested in the 1940s that a group of ferns related to Notholaena nivea might represent a distinct genus of its own. [12] [13] Weatherby thought that, until that genus was described, the group might better be placed in Pellaea, rather than in Notholaena, but died in 1949 before he could circumscribe and publish it. Accordingly, in 1950, Conrad Vernon Morton transferred the species to Pellaea as P. limitanea, to provide a name for it in Thomas Henry Kearney's Flowering Plants and ferns of Arizona, and reduced the subspecies to a variety. [14] John T. Mickel, following Copeland's opinion that Notholaena was best lumped into a broadly defined Cheilanthes , transferred the species there as C. limitanea in 1979, also treating the subspecies as a variety. [15]

The recognition of the N. nivea group as a genus was finally addressed in 1987 by Michael D. Windham, who was carrying out phylogenetic studies of the cheilanthoids. He elevated Notholaena sect. Argyrochosma to become the genus Argyrochosma , [16] and transferred this species to that genus as A. limitanea. [17] He did not create a combination for N. limitanea subsp. mexicana at the time, but did so (at subspecific rank) in 1993. [18] In 2018, Maarten J. M. Christenhusz transferred the species to Hemionitis as H. limitanea, as part of a program to consolidate the cheilanthoid ferns into that genus. [19]

Phylogenetic studies have shown that A. limitanea is a sister species to A. dealbata , of the central and southern United States; these two species form a clade sister to another clade of several South American species. [20] The two subspecies are genetically distinct, and believed to be of independent allopolyploid origin, through the hybridization of sexual taxa not yet discovered. More than one cryptic allopolyploid taxon may be included within the present circumscription of A. limitanea subsp. limitanea. [21]

Distribution and habitat

Argyrochosma limitanea is known in the United States from San Bernardino County, California, east through Arizona, New Mexico, southern Utah, and Trans-Pecos Texas, [22] and south into northern Mexico, extending as far southeast as Hidalgo. [7] A. limitanea subsp. limitanea ranges from California through Utah and into Mexico only in Sonora and Chihuahua. A. limitanea subsp. mexicana has a more easterly range, from Arizona through Texas and in Mexico from Chihuahua and Sinaloa east. [7] [5]

Both subspecies grow on rocky slopes and cliffs, composed of either calcareous or volcanic rocks, [7] [5] [4] although A. limitanea subsp. mexicana shows a greater preference for calcareous substrates in Mexico. [7] A. limitanea subsp. limitanea is found at an altitude from 800 to 2,300 meters (2,600 to 7,500 ft), while A. limitanea subsp. mexicana, growing in the mountains, occurs from 1,500 to 2,500 meters (4,900 to 8,200 ft). [7] [5]

Conservation

Under the NatureServe conservation status system, A. limitanea is ranked as apparently secure (G4), but it is considered imperiled in Texas. [1]

Notes and references

Related Research Articles

<i>Argyrochosma</i> Genus of ferns in the family Pteridaceae

Argyrochosma is a genus of ferns known commonly as false cloak ferns. The genus is included in the Cheilanthoideae subfamily of the Pteridaceae. 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. These ferns, of which there are about 20 species, are mostly native to the Americas, from North to South and including the Caribbean, while one species, A. connectens, is known from Sichuan, China. They are commonly found growing in cracks between rocks. Their leaves are generally shorter than 40 centimeters 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.

<i>Argyrochosma jonesii</i> Species of fern in the family Pteridaceae

Argyrochosma jonesii, known as Jones' false cloak fern, is a species of fern native to the southwestern United States and Sonora, Mexico. It grows on calcareous rocks, and has small, finely-divided leaves with a leathery texture and dark axes connecting the leaf segments. Unlike many members of Argyrochosma, it does not secrete white powder on the underside of its leaves. First described as a species in 1917, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

<i>Argyrochosma nivea</i> Species of fern in the family Pteridaceae

Argyrochosma nivea is an Andean fern species in the genus Argyrochosma.

Myriopteris aemula, the Texas lip fern or rival lip fern, is a moderately-sized fern of Texas and Mexico, a member of the family Pteridaceae. Unlike many members of its genus, its leaves have a few hairs on upper and lower surfaces, or lack them entirely. One of the cheilanthoid ferns, it was usually classified in the genus Cheilanthes as Cheilanthes aemula until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows on limestone rock.

<i>Argyrochosma dealbata</i> Species of fern in the family Pteridaceae

Argyrochosma dealbata, the powdery false cloak fern, is a small fern endemic to the central and southern United States. It grows on calcareous rocks, such as limestone. Its leaves are highly divided, with leaf segments joined by shiny, chestnut-brown axes, and their undersides are coated with white powder, giving the fern its name. First described as a species in 1814, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

Argyrochosma connectens is a small cheilanthoid fern endemic to Sichuan, China. It is the only member of its genus known from Asia. Relatively rare, it is found growing in the crevices of limestone rocks in hot, dry valleys. The species was long classified in the genus Pellaea, but after a phylogenetic study in 2015 was transferred to Argyrochosma.

Argyrochosma delicatula is a fern known from northeastern Mexico. It grows in rocky habitats, either in sun or in shade, and is distinguished from similar species by the presence of pale yellow powder on the underside of its leaves. First described as a species in 1939, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

<i>Argyrochosma peninsularis</i> Species of fern in the family Pteridaceae

Argyrochosma peninsularis is a fern endemic to Baja California Sur. It grows in dry, rocky places. First described as a species in 1939, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns". A dusting of powdery material and the presence of occasional scales on the central axis of its leaves help distinguish it from related species.

Argyrochosma pallens is a fern endemic to Mexico. It has narrow, divided leaves with brown axes; the leaves are dusted with white powder above and coated in it below. First described as a species in 1956, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

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 in 1987, recognizing their distinctness from the "cloak ferns".

Argyrochosma stuebeliana is a fern endemic to Peru. Its highly divided, leathery leaves are coated with white powder on their under surface. Originally described as a variety of Argyrochosma dealbata in 1909, based on a single leaf collected by Alphons Stübel, whom its name honors, it was recognized as a distinct species in 1961, distinguished from similar members of the genus largely by its round leaf segments. It was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

<i>Myriopteris aurea</i> Species of fern

Myriopteris aurea, the golden lip fern or Bonaire lip fern, is a moderately-sized fern native to the Americas, a member of the family Pteridaceae. Unlike many members of its genus, its leaf is only modestly dissected into lobed leaflets (pinnae), which are hairy both above and below. One of the cheilanthoid ferns, until 2013 it was classified in the genus Cheilanthes as Cheilanthes bonariensis, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows on dry, rocky slopes, and ranges from Mexico, where it is common and widespread, and the southwestern United States south and east through Central and South America as far as Chile and Argentina.

Argyrochosma lumholtzii is a rare fern in the family Pteridaceae known from Sonora, Mexico. It is quite similar to Jones' false cloak fern, but has black leaf axes and a less highly divided leaf. First described as a species in 1939, honoring the explorer Carl Sofus Lumholtz, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

<i>Argyrochosma fendleri</i> Species of fern in the family Pteridaceae

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 in 1987, recognizing their distinctness from the "cloak ferns".

Argyrochosma incana, the hairy false cloak fern, is a fern known from the southwestern United States through Mexico to Guatemala, and from a disjunct population in the Dominican Republic. It grows on rocky slopes and steep banks, often in forests. Like many of the false cloak ferns, it bears white powder on the underside of its leaves. First described as a species in 1825, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

Argyrochosma palmeri is a fern endemic to Mexico. It has narrow, divided leaves with black axes; the leaves are coated in white powder below, and sparsely dusted or free of it above. First described as a species in 1887, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

Argyrochosma pilifera is a fern endemic to Mexico. It has lance-shaped, divided leaves with dark purple axes; the undersides of the leaves are coated in white powder. First described as a species in 1956, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

<i>Argyrochosma formosa</i> Species of fern in the family Pteridaceae

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 in 1987, recognizing their distinctness from the "cloak ferns".

<i>Argyrochosma microphylla</i> Species of fern in the family Pteridaceae

Argyrochosma microphylla, the small-leaf false cloak fern, is a species of fern native to New Mexico, Texas and northern Mexico. It grows on limestone rocks and cliffs, and has finely-divided leaves with small leaf segments, often folded in half when dry, which lack the white powder present on the leaf underside of many related species. First described as a species in 1869, it was transferred to the new genus Argyrochosma in 1987, recognizing their distinctness from the "cloak ferns".

<i>Myriopteris rufa</i> Species of fern

Myriopteris rufa, commonly known as Eaton's lip fern, is a moderately-sized fern of Mexico and the southwestern United States, with outlying populations in Costa Rica and the Appalachian Mountains. One of the cheilanthoid ferns, it was usually classified in the genus Cheilanthes, as Cheilanthes eatonii, until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows in rocky habitats, most frequently on limestone but also sometimes on basalt or shale.

References

  1. 1 2 NatureServe 2020.
  2. 1 2 3 4 Mickel & Smith 2004, p. 67.
  3. 1 2 3 4 5 6 7 8 9 10 Tryon & Weatherby 1956, p. 86.
  4. 1 2 3 4 5 6 7 8 9 10 11 Lellinger 1985, p. 161.
  5. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Windham 1993.
  6. ↑ Mickel & Smith 2004, pp. 67–68.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Mickel & Smith 2004, p. 68.
  8. ↑ Maxon 1919, p. 73.
  9. ↑ Maxon 1919, p. 70.
  10. ↑ Maxon 1919, p. 72.
  11. ↑ Farwell 1931, p. 283.
  12. ↑ Morton 1950, pp. 249–250.
  13. ↑ Windham 1987, p. 37.
  14. ↑ Morton 1950, pp. 249–251.
  15. ↑ Mickel 1979, pp. 434–435.
  16. ↑ Windham 1987, p. 38.
  17. ↑ Windham 1987, p. 40.
  18. ↑ Windham 1993a, p. 32.
  19. ↑ Christenhusz, Fay & Byng 2018, p. 17.
  20. ↑ Sigel et al. 2011, pp. 558, 561.
  21. ↑ Sigel et al. 2011, p. 561.
  22. ↑ Kartesz 2014.

Works cited

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