Asplenium

Asplenium
	Maidenhair spleenwort (Asplenium trichomanesssp.quadrivalens)
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Division:	Polypodiophyta
Class:	Polypodiopsida
Order:	Polypodiales
Suborder:	Aspleniineae
Family:	Aspleniaceae
Genus:	Asplenium; L.
Type species
	Asplenium marinum; L.
Species
	About 700, but see text.
Synonyms
	Camptosorus; Ceterach; LoxoscapheT.Moore; Phyllitis; Tarachia; and see text

Aspleniumis agenusof about 700speciesofferns,often treated as the only genus in thefamily Aspleniaceae,though other authors considerHymenaspleniumseparate, based onmolecular phylogeneticanalysis ofDNA sequences,a different chromosome count, and structural differences in the rhizomes. Thetype speciesfor the genus isAsplenium marinum.

The most common vernacular name isspleenworts,applied to the more "typical" species.A. nidusand several similar species are calledbird's-nest ferns,theCamptosorusgroup is known aswalking ferns,and distinct names are applied to some other particularly well-known species.

Taxonomy and genetics

Many groups of species have been separated fromAspleniumassegregategenera. These includeCamptosorus,Ceterach,Phyllitis,andTarachia,but these species can formhybridswith otherAspleniumspecies and because of this are usually included in a more broadly definedAsplenium.^[1]

Some of the older classifications elevate the Aspleniaceae to thetaxonomic rankoforderas Aspleniales. The newer classifications place it in the subordinal group called eupolypods within the orderPolypodiales.Within the eupolypods, Aspleniaceae belongs to acladeinformally and provisionally known as eupolypods II.

It has been found that in some species, thechloroplast genomehasevolvedin complex and highly unusual ways. This makes standardcladisticanalyses unsuited to resolve thephylogenyof that particular group of ferns, and even very sophisticatedcomputational phylogeneticsmethods yield little information. In addition to hybridization running rampant in parts of this genus, there are also some species like themother spleenwort(A. bulbiferum) orA. viviparumwhich mainlyreproduce asexually,essentiallycloningthemselves over and over again. While most arediploidortetraploid,some species (e.g.A. shuttleworthianum) are octoploid.^[2]

Uses

Both the scientific name and the common name "spleenwort" are derived from an old belief, based on thedoctrine of signatures,that the fern was useful for ailments of thespleen,^[3]due to the spleen-shapedsorion the backs of thefronds."-wort" is an ancient English term that simply means "plant"(compareGerman-wurz). The plants were thought to causeinfertilityin women.^[3]

Vitruviusrelates the story of the name thus:

... certain pastures in Crete, on each side of the river Pothereus, which separates the two Cretan states of Gnosus and Gortyna. There are cattle at pasture on the right and left banks of that river, but while the cattle that feed near Gnosus have the usual spleen, those on the other side near Gortyna have no perceptible spleen. On investigating the subject, physicians discovered on this side a kind of herb which the cattle chew and thus make their spleen small. The herb is therefore gathered and used as a medicine for the cure of splenetic people. The Cretans call it ἄσπληνον. "Book I".Ten Books on Architecture– viaWikisource.

A few of these ferns have some economic importance in thehorticulturetrade. Thebird's-nest ferns(A. nidusand several very similar, closely related species) are commonly found for sale as ahouse plant.The Australianmother spleenwort(A. bulbiferum) is sometimes available atgreenhouses,and is of interest, along with the relatedA. viviparum,for the many small bulblets borne on the fronds that may grow into new plants. This characteristic is also shared with the eastern North Americanwalking fern(A. rhizophyllum) and several Mexican species includingA. palmeri.Theebony spleenwortA. platyneuronis also sometimes sold in nurseries as a hardy plant. However, many spleenworts are epipetric orepiphyticand difficult to cultivate.

Aspleniumspecies are used as food plants by thelarvaeof someLepidopteraspecies includingBatrachedra bedelliellawhich feeds exclusively onA. nidus.For diseases ofAsplenium,seeList of foliage plant diseases (Polypodiaceae).