Argyrochosma connectens

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Argyrochosma connectens
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Order: Polypodiales
Family: Pteridaceae
Genus: Argyrochosma
Species:
A. connectens
Binomial name
Argyrochosma connectens
(C.Chr.) G. M. Zhang
Synonyms
  • Hemionitis connectens(C.Chr.) Christenh.
  • Pellaea connectensC.Chr.

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 .

Contents

Description

Argyrochosma connectens is a small, epipetric fern that puts up leaves in tight clusters. Leaf stalks and axes are a shiny brown; the leaves have a papery texture, and unlike many members of the genus, are free of light-colored farina (a powdery flavonoid secretion) beneath.

The rhizome is short and upright, bearing thin, twisted brown scales of uniform color, subulate-lanceolate in shape. [1] Fronds spring from the rhizome in dense clusters. The stipe (the stalk of the leaf, below the blade) is dark brown, round, and brittle, about 3 to 8 centimeters (1 to 3 in) long. A few scales similar to those of the rhizome are scattered at its base; narrowed, hairlike scales sometimes continue further up the stipe. [1] The rachis (leaf axis) is straight, and the rachis, costae and costules (axes of leaflets and leafules) are all shiny and chestnut-brown in color. [1]

The blade tissue turns brownish-green when dried; it is papery in texture, and both sides lack scales, hairs, or farina. [1] The leaf blades are lanceolate or somewhat oblong-triangular, measuring 5 to 10 centimeters (2 to 4 in) long and 2 to 4 centimeters (0.8 to 2 in) wide. They are bipinnate (divided into pinnae and pinnules) or occasionally tripinnate. [1] Each blade is divided into 7 to 21 pinnae, set at an oblique angle to the rachis. The lowest or second lowest pair of pinnae are the largest, their size gradually diminishing towards the apex of the blade. [1] The blade apex is capped with a distinct terminal leaf segment, of the width of a typical pinnule at its base and short-acuminate at its apex. [1] The pinnae are borne on stalks 1 to 3 millimeters (0.04 to 0.1 in) long. Larger pinnae also have a distinct pinnule at their apex, and are divided into 3 to 9 pinnules; the smaller pinnae are undivided. The pinnules are borne on short stalks. They are not fused with one another and do not have lobes, and are widest near the base or near the middle. They are 3 to 6 millimeters (0.1 to 0.2 in) long and 2 to 3 millimeters (0.08 to 0.1 in) wide, oblong to ovate in shape. The base of each pinnule is rounded to truncate (abruptly cut off), and the apex is rounded or obtuse (blunt). [1]

The sori occur at vein tips, and tend to merge with each other; the continuous band of sori on a leaf segment is sometimes broken at the segment tip. They are protected by the margin of the leaf curling under to form a false indusium. These are not well differentiated from the rest of the leaf, and are narrow and pale green in color, with wavy or irregular margins. [1] The sporangia contain 64 spores. Plants are sexual diploids, with a chromosome number of 2n = 54. [2] Spores are brown and have a rough surface, similar to those of A. incana but coarser in texture. [3]

Taxonomy

The species was originally described by Carl Christensen in 1924 as Pellaea connectens. [4] Genera in the cheilanthoid ferns have proven difficult to circumscribe due to homoplasy, and Christensen bestowed its epithet because he considered it to connect, by morphological intermediacy, the genera Adiantopsis , Cheilanthes , Notholaena and Pellaea . [5] Progress in fern taxonomy has resulted in the subdivision of several of these genera: in particular, a group of ferns, frequently bearing farina on the leaf underside and previously placed either in Notholaena or Pellaea as sect. Argyrochosma, were elevated to become the genus Argyrochosma by Michael D. Windham in 1987. [6] Windham's work involved New World cheilanthoids, and did not encompass Asian species. Gangmin Zhang and co-workers were able to obtain material of Pellaea connectens for DNA analysis, and showed in 2015 that it in fact belonged within the clade described by Windham as Argyrochosma, transferring it to that genus as A. connectens. [7] In 2018, Maarten J. M. Christenhusz transferred the species to Hemionitis as H. connectens, as part of a program to consolidate the cheilanthoid ferns into that genus. [8]

The 2015 phylogenetic study showed that A. connectens is sister to a clade containing the farinose species A. dealbata and A. limitanea ; together, the three are sister to a clade containing A. chilensis , A. nivea sensu lato and A. stuebeliana . [9] The lack of farina production in A. connectens is believed to have evolved after it diverged from its sister species. [3]

Distribution and habitat

Argyrochosma connectens is endemic to southern and southwestern Sichuan. It is rare, growing in the crevices of limestone rocks in hot, dry valleys at an altitude of 1,900 to 2,800 meters (6,200 to 9,200 ft). [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 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.

<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.

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

Myriopteris alabamensis, the Alabama lip fern, is a moderately-sized fern of the United States 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 alabamensis until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows in shade on limestone outcrops.

Myriopteris allosuroides is a moderately-sized fern of Mexico, a member of the family Pteridaceae. Unlike many members of its genus, its rachides are grooved on the upper surface and largely free of hairs or scales. One of the cheilanthoid ferns, it was usually classified in the genera Cheilanthes or Pellaea until 2013, when the genus Myriopteris was again recognized as separate from Cheilanthes. It typically grows on dry, rocky slopes over acidic, particularly basaltic, 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 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".

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 limitanea</i> Species of fern in the family Pteridaceae

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 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 rawsonii</i> Species of fern

Myriopteris rawsonii, formerly known as Cheilanthes rawsonii, is a perennial fern native to Namaqualand in Southern Africa. Like many other cheilanthoid ferns, it is adapted to dry conditions, bearing a thick layer of pale hairs on the underside of its pinnate-pinnatifid leaves. It is the only African representative of its clade of cheilanthoids, the otherwise American genus Myriopteris. It spends much of the year in a dried-out, dormant state, rehydrating and putting out new growth during winter rains. Its name honors the botanist and civil servant Sir Rawson W. Rawson.

References

  1. 1 2 3 4 5 6 7 8 9 10 Zhang & Yatskievych 2013.
  2. ↑ Zhao, Yang & Zhang 2016.
  3. 1 2 Wang et al. 2015, p. 36.
  4. ↑ Christensen 1924, p. 89.
  5. ↑ Bower 1928, p. 84.
  6. ↑ Windham 1987, p. 38.
  7. ↑ Wang et al. 2015, p. 37.
  8. ↑ Christenhusz, Fay & Byng 2018, p. 12.
  9. ↑ Wang et al. 2015, p. 33.

Works cited

  • Bower, F. O. (1928). The ferns (Filicales) treated comparatively with a view to their natural classification. Vol. III The Leptosporangiate Ferns. Cambridge: Cambridge University Press.
  • Christenhusz, Maarten J. M.; Fay, Michael F.; Byng, James W. (2018). Plant Gateway's the Global Flora: A practical flora to vascular plant species of the world. Vol. 4. ISBN   978-0-9929993-9-1.
  • Christensen, Carl (1924). "Plantae sinensis III Pteridophyta". Acta Horti Gothoburgensis. 1.
  • Windham, Michael D. (1987). "Argyrochosma, a new genus of cheilanthoid ferns". American Fern Journal. 77 (2): 37–41. doi:10.2307/1547438. JSTOR   1547438.
  • Zhang, Gangmin; Yatskievych, George (2013). "Pellaea connectens". In Zhengyi, Wu; Raven, Peter H.; Deyuan, Hong (eds.). Flora of China. Vol. 2–3: Pteridophytes. Beijing and St. Louis: Science Press & Missouri Botanical Garden.
  • Wang, Wan; Yang, Wenli; Mao, Xingxing; Zhao, Ranran; Dou, Ping; Zhang, Gangmin (2015). "The phylogenetic affinities of Pellaea connectens, a rare endemic Chinese fern". Phytotaxa. 220 (1). doi:10.11646/phytotaxa.220.1.2.
  • Zhao, Ranran; Yang, Wenli; Zhang, Gangmin (2016). "A study of chromosome and gametophyte development in Pellaea connectens C. Chr". Phytotaxa. 266 (3). doi:10.11646/phytotaxa.266.3.4.
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