''Vandenboschia boschiana'',

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

''Trichomanes boschianum'', the Appalachian bristle fern or Appalachian filmy fern, is a small delicate perennial leptosporangiate

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

which forms colonies with long, black creeping rhizomes. The evergreen fronds are bipinnatifid, deeply and irregularly dissected, about 4 to 20 cm long, 1 to 4 cm across with winged

stipes Crucifixion is a method of capital punishment in which the victim is tied or nailed to a large wooden cross or beam and left to hang until eventual death from exhaustion and asphyxiation. It was used as a punishment by the Persians, Carthagin ...

1 to 7 cm long and light green in colour. The common name derives from the leaves which are very thin, only a single cell thick, missing an

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...

and translucent, giving the appearance of a wet film. Sori, the spore-producing organs are formed along the margins of the frond segments. The

indusium A sorus (pl. sori) is a cluster of sporangia (structures producing and containing spores) in ferns and fungi. A coenosorus (plural coenosori) is a compound sorus composed of multiple, fused sori. Etymology This New Latin word is from Ancient ...

forms a funnel around the sorus which is sunken in the leaf tissue. A bristle-like receptacle protrudes from the indusium as in all ''Trichomanes'' species.

Spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

production occurs between July and September. In common with all ferns, ''V. boschiana'' exhibits a

gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...

stage in its life cycle (

alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the predominant type of Biological life cycle, life cycle in plants and algae. It consists of a Multicellular organism, multicellular haploid sexual phase, the gametophy ...

) and develops a

haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

reproductive

prothallus A prothallus, or prothallium, (from Latin ''pro'' = forwards and Greek ''θαλλος'' (''thallos'') = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young ...

as an independent plant. In contrast to the typical heart-shaped fern

, ''V. boschiana'' gametophytes are filamentous and resemble colonies of

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

or moss

protonemata A protonema (plural: protonemata) is a thread-like chain of cells that forms the earliest stage of development of the gametophyte (the haploid phase) in the life cycle of mosses. When a moss first grows from a spore, it starts as a ''germ tube'', ...

Taxonomy

According to the Flora of North America

ploidy Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mat ...

is rather variable. The western colonies tend to be

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

whilst the eastern ones are mostly tetraploid. Sterile triploids have also been recorded. It has been hypothesized that most of the populations of ''V. boschiana'' are genetically identical clones of great age.Hill, S.R. (2003). Conservation Assessment for Appalachian Bristle Fern (''Trichomanes boschianum'') Sturm. USDA Forest Service, Eastern Region

Distribution

Endemic to eastern North America. A single disjunct population has been found in Chihuahua, Mexico. Populations are found in the eastern United States from southern Ohio in the north to Alabama in the south and from Arkansas and southern Illinois in the west to South Carolina in the east. In all areas the populations are very scattered and reflect the distribution of an uncommon habitat.

Ecology and conservation

''Vandenboschia boschiana'' is found in deep shade on damp acid rocks, usually sandstone, of sheltered canyons, grottos and rock shelters at an altitude of 150 to 800 m. The rock outcrops are generally found within mesic upland forests. This fern is dependent upon a constantly high air humidity which places severe restrictions on its distribution in the current climate of eastern North America. In fact ''V. boschiana'' is believed to be a relict of milder pre-glacial conditions. The current distribution of ''V. boschiana'' is considered to reflect historical lack of glaciation, substrate, type of bedrock, lack of disturbance in the surrounding forest and

micro-climate A microclimate (or micro-climate) is a local set of atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few squa ...

. Temperature is perhaps less important than these factors though extreme cold weather can apparently cause mortality.Cusick, A. (1983). Trichomanes boschianum in Ohio. Ohio DNR Periodic droughts do cause heavy mortality and have reduced many population sizes over the last few decades.Farrar, D.R. (1993). Hymenophyllaceae, In: Flora of North America Editorial Committee, eds., Flora of North America, Vol. 2. Oxford University Press. New York. The species is probably more at risk than its G4 grading would suggest and state NatureServe conservation rankings are Vulnerable (S3) to Critically imperiled (S1). Hazards include drying of the habitat, removal of forest canopy shading the rock exposures and over-collecting.

Cultivation and uses

The plant is not known to be widely cultivated. From its large-scale distribution the plant may be hardy to USDA Zone 6, although this may not reflect the micro-climate of its sheltered habitat.

References

External links

*
Flora of North America: ''Trichomanes boschianum''Global Biodiversity Information Facility (GBIF) Data Portal: ''Trichomanes boschianum''Ohio DNR: ''Trichomanes boschianum''University of Tennessee Herbarium: ''Trichomanes boschianum''Conservation Assessment for Appalachian Bristle Fern