Ebony spleenwort

Asplenium platyneuron

''Asplenium platyneuron'' , commonly known as ebony spleenwort or brownstem spleenwort, is a fern native to North America east of the Rocky Mountains and to South Africa. It takes its common name from its dark, reddish-brown, glossy stipe and rachis , which bear a once-divided, pinnate leaf. The fertile fronds, which die off in the winter, are darker green and stand upright, while the sterile fronds are evergreen and lie flat on the ground. An auricle at the base of each pinna points towards the tip of the frond. The dimorphic fronds and alternate, rather than opposite, pinnae distinguish it from the similar black-stemmed spleenwort.

The species was first described in 1753 by Linnaeus as ''Acrostichum platyneuros'', although Linnaeus' type drew on material from several other species as well. It was more commonly called ''Asplenium ebeneum'', a name published by William Aiton in 1789, until the rediscovery and revival of the Linnaean epithet in the late Nineteenth Century. A number of forms and varieties of the species have been described, but few are recognized today; in particular, larger and more fertile specimens, those with more or less toothed leaves, and those with proliferating buds are considered to fall within the natural range of variation of the species, and do not require taxonomic distinction. ''A. platyneuron'' f. ''hortonae'', a sterile form with the pinnae cut to toothed pinnules, and f. ''furcatum'', with forking fronds, are still recognized.

The formation of proliferating buds is one of several unusual adaptations for reproduction in this species. The buds form near the base of the stipe, and when covered with soil, can grow into new individuals as the frond that bore them dies. Ebony spleenwort is also well-adapted to propagate by spores: the upright sterile fronds help the spores enter the airstream for long-distance dispersal, and a low genetic load allows spores that have grown into a gametophyte to self-fertilize with a high degree of success. This dispersal ability seems to have helped the species spread rapidly in the Great Lakes region in the late 20th century. Long-distance dispersal may also explain its naturalized appearance in South Africa; the same mechanism may have given rise to an isolated population found in Slovakia in 2009, its first known occurrence in Europe.

Ebony spleenwort has broad habitat preferences, growing both on rocks like many other North American spleenworts and in a variety of soils. Unlike many other spleenworts, it is not particularly sensitive to soil pH. It hybridizes with several other spleenworts, particularly mountain spleenwort and walking fern; these species, their sterile hybrid offspring, fertile allotetraploid hybrids, and backcrosses between allotetraploids and the parents are collectively known as the "Appalachian ''Asplenium'' complex". Two hybrids between ''A. platyneuron'' and spleenworts outside of this complex are also known.
Ebony Spleenwort (Asplenium platyneuron) On a shaded hillside at the base of a ridge at the edge of a dense mixed hardwood/coniferous forest in NW Georgia (Gordon County), US.
https://www.jungledragon.com/image/60067/ebony_spleenwort_asplenium_platyneuron.html Asplenium platyneuron,Ebony spleenwort,Geotagged,Spring,United States

Appearance

Ebony spleenwort is a small fern with pinnate fronds, growing in tufts, with a shiny reddish-brown stipe and rachis. The fronds are dimorphic, with long, erect, dark green fertile fronds, which are deciduous, and shorter, spreading, lighter green sterile fronds, which are evergreen.The species most similar to ''Asplenium platyneuron'' is the black-stemmed spleenwort, ''A. resiliens''. However, this stipe of this species is darker, and the pinnae are opposite, rather than alternate, along the rachis. Neither black-stemmed spleenwort nor the other pinnate American spleenworts have dimorphic fertile and sterile fronds. It might be confused with a young Christmas fern, ''Polystichum acrostichoides'', but that species is generally much larger and has a green, scaly stipe and rachis. It is very similar to Boydston's spleenwort, ''Asplenium × boydstoniae'', a backcross with Tutwiler's spleenwort, ''Asplenium tutwilerae''; however, Boydston's spleenwort has an elongated, acute frond tip similar to that of Tutwiler's spleenwort. Confusion with a Boydston's spleenwort is effectively impossible, as Boydston's spleenwort only grows wild at one location on Earth.
Ebony Spleenwort (Asplenium platyneuron) On a shaded hillside at the base of a ridge at the edge of a dense mixed hardwood/coniferous forest in NW Georgia (Gordon County), US.
https://www.jungledragon.com/image/60066/ebony_spleenwort_asplenium_platyneuron.html Asplenium platyneuron,Ebony spleenwort,Geotagged,Spring,United States

Distribution

In North America, ''A. platyneuron'' is native throughout the eastern United States from southern Maine to the southeastern corner of Wisconsin, south to Florida and west to eastern Nebraska, Kansas, Oklahoma, and Texas, and in the far southeast of Canada. It is also found around the meeting point of Colorado, New Mexico, and Oklahoma, and in isolated small populations in New Mexico, Arizona and the West Indies. Outside of North America, ''A. platyneuron'' is found in tropical and subtropical southern Africa, a distribution not known for any other North American fern. An isolated population was found on serpentine soil in an oak woodland in Slovakia in 2009. Since the 1960s, ''A. platyneuron'' has spread rapidly and aggressively in the Great Lakes region, where it was formerly uncommon.

''Asplenium platyneuron'' can be found in a wide variety of habitats, at altitudes from 0 to 1,300 meters . It will tolerate soils ranging from mediacid to subalkaline , although it prefers subacid soils over mediacid. Unlike many other North American spleenworts, it can grow on soil as well as rock. When growing in soil, it can be found in forests and woodlands, including sandy pinelands, as well as old fields and other disturbed sites. It can colonize a variety of rocks, particularly calcareous ones, and will also grow on mortared walls. In South Africa, it is generally found at altitudes over 600 meters , in habitats similar to those it prefers in North America .
Ebony Spleenwort (Asplenium platyneuron) Growing under an oak tree in a dense mixed forest. Asplenium platyneuron,Ebony spleenwort,Geotagged,Spring,United States

Status

Protein extracts from ''A. platyneuron'' have been shown to deter insect predation on soybeans to a significant extent, and the Missouri Botanical Garden describes it as lacking "serious insect or disease problems". However, a population of several hundred individuals in Florida was reported to have been almost wiped out by insect activity. It is susceptible to slugs. The black fern aphid has been reported to feed on it.

Sporophytes are fairly tolerant of drought, but require well-drained soils. The prothallia of ''A. platyneuron'' can survive periods of drought for up to a month. There is some evidence to show that the prothallia may undergo clonal reproduction and fission, which has been induced in the laboratory through variations in light intensity.

A variety of adaptations make ''A. platyneuron'' an aggressive colonizer, even weedy, when compared with other spleenworts, although a warming climate and an increase in second growth habitats may also have played a role in its expansion in the Great Lakes region. It tolerates broad variation in soil conditions, including pH, and will grow in both sun and shade. The starchy stipe bases provide energy for rapid growth in the spring, allowing the fronds to keep ahead of competing vegetation. The erect fertile fronds, unusual for ''Asplenium'', help release spores into the wind for long-distance dispersal, while the proliferative buds allow clonal propagation in moist, fertile habitats. The species also carries a very low genetic load, so that viable sporophytes can develop from intragametophytic self-fertilization with 83–89% success. This means that new sporophytes can usually grow from the gametophyte formed from a single spore. This has allowed ebony spleenwort to be an early colonizer, from distant locations, of recently disturbed habitats, such as coal spoils in southern Iowa. The appearance of ''A. platyneuron'' in a disturbed habitat in Slovakia, 6,500 kilometers from the nearest known sites in eastern North America, is probably the result of long-distance dispersal, which may also have allowed it to colonize and naturalize in South Africa.

While globally secure, ebony spleenwort is considered an endangered species in some of the states and provinces at the northern and western edges of its North American range. NatureServe considers it to be critically imperiled in Arizona and Colorado, imperiled in Nebraska, Maine, Rhode Island, and Quebec, and vulnerable in Minnesota.

Habitat

In North America, ''A. platyneuron'' is native throughout the eastern United States from southern Maine to the southeastern corner of Wisconsin, south to Florida and west to eastern Nebraska, Kansas, Oklahoma, and Texas, and in the far southeast of Canada. It is also found around the meeting point of Colorado, New Mexico, and Oklahoma, and in isolated small populations in New Mexico, Arizona and the West Indies. Outside of North America, ''A. platyneuron'' is found in tropical and subtropical southern Africa, a distribution not known for any other North American fern. An isolated population was found on serpentine soil in an oak woodland in Slovakia in 2009. Since the 1960s, ''A. platyneuron'' has spread rapidly and aggressively in the Great Lakes region, where it was formerly uncommon.

''Asplenium platyneuron'' can be found in a wide variety of habitats, at altitudes from 0 to 1,300 meters . It will tolerate soils ranging from mediacid to subalkaline , although it prefers subacid soils over mediacid. Unlike many other North American spleenworts, it can grow on soil as well as rock. When growing in soil, it can be found in forests and woodlands, including sandy pinelands, as well as old fields and other disturbed sites. It can colonize a variety of rocks, particularly calcareous ones, and will also grow on mortared walls. In South Africa, it is generally found at altitudes over 600 meters , in habitats similar to those it prefers in North America .Protein extracts from ''A. platyneuron'' have been shown to deter insect predation on soybeans to a significant extent, and the Missouri Botanical Garden describes it as lacking "serious insect or disease problems". However, a population of several hundred individuals in Florida was reported to have been almost wiped out by insect activity. It is susceptible to slugs. The black fern aphid has been reported to feed on it.

Sporophytes are fairly tolerant of drought, but require well-drained soils. The prothallia of ''A. platyneuron'' can survive periods of drought for up to a month. There is some evidence to show that the prothallia may undergo clonal reproduction and fission, which has been induced in the laboratory through variations in light intensity.

A variety of adaptations make ''A. platyneuron'' an aggressive colonizer, even weedy, when compared with other spleenworts, although a warming climate and an increase in second growth habitats may also have played a role in its expansion in the Great Lakes region. It tolerates broad variation in soil conditions, including pH, and will grow in both sun and shade. The starchy stipe bases provide energy for rapid growth in the spring, allowing the fronds to keep ahead of competing vegetation. The erect fertile fronds, unusual for ''Asplenium'', help release spores into the wind for long-distance dispersal, while the proliferative buds allow clonal propagation in moist, fertile habitats. The species also carries a very low genetic load, so that viable sporophytes can develop from intragametophytic self-fertilization with 83–89% success. This means that new sporophytes can usually grow from the gametophyte formed from a single spore. This has allowed ebony spleenwort to be an early colonizer, from distant locations, of recently disturbed habitats, such as coal spoils in southern Iowa. The appearance of ''A. platyneuron'' in a disturbed habitat in Slovakia, 6,500 kilometers from the nearest known sites in eastern North America, is probably the result of long-distance dispersal, which may also have allowed it to colonize and naturalize in South Africa.

While globally secure, ebony spleenwort is considered an endangered species in some of the states and provinces at the northern and western edges of its North American range. NatureServe considers it to be critically imperiled in Arizona and Colorado, imperiled in Nebraska, Maine, Rhode Island, and Quebec, and vulnerable in Minnesota.

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Status: Unknown
EX EW CR EN VU NT LC
Taxonomy
KingdomPlantae
DivisionPolypodiophyta
ClassPolypodiopsida
OrderPolypodiales
FamilyAspleniaceae
GenusAsplenium
SpeciesA. platyneuron