Ebony spleenwort

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.

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 .

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.