Psilotum is a genus of
fernA fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
-like
vascular plantVascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s, one of two genera in the family
PsilotaceaePsilotaceae is a family of fern-like plants consisting of two genera, Psilotum and Tmesipteris. The two genera are very different and in the past Tmesipteris has been placed in its own family, Tmesipteridaceae, but most classifications continue to treat it in Psilotaceae...
, order
Psilotales, and class
Psilotopsida (the other being
TmesipterisTmesipteris the "hanging fork fern", is a genus of fern-like vascular plants, one of two genera in the family Psilotaceae, order Psilotales, and class Psilotopsida ....
). The name of the genus is from Greek
psilos = naked, because it lacks organs, such as leaves, normally found in other ferns.
Species and distribution
There are two species,
Psilotum nudum and
Psilotum complanatum, with a hybrid between them known,
Psilotum × intermedium W. H. WagnerWarren H. Wagner Jr. , known as Herb Wagner, from his middle name, "Herbert," was an eminent American botanist who lived in Michigan...
.
The distribution of
Psilotum is tropical and subtropical, in the
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,
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, and the Pacific, with a few isolated populations in SW Europe. The highest latitudes known are in
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,
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province in
SpainSpain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, and southern
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for
P. nudum. In the U.S., one species is found from Florida to Texas, the other in Hawaii.
Relation to ferns
Psilotum superficially resembles some rhyniophytes in having apparently dichotomous branching, terminal sporangia and a lack of roots. However, careful study of the morphology and anatomy suggested that whisk ferns were not closely related to rhyniophytes.
Molecular evidence strongly confirms that
Psilotum is a fern. Psilophytes are sister to ophioglossoid ferns.
Gametophyte
The
gametophyteA gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
of
Psilotum nudum L. Beauv. (
P. triquetrum Swartz) is unusual in that it branches dichotomously, lives underground and possesses vascular tissue. The nutrition of the gametophyte appears to be myco-heterotrophic, assisted by
endophyticAn endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life without causing apparent disease. Endophytes are ubiquitous and have been found in all the species of plants studied to date; however, most of these endophyte/plant relationships...
fungi.