Psilotum
| Psilotum | |
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| Closeup of Psilotum nudum | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Pteridophyta |
| Class: | Psilotopsida |
| Order: | Psilotales |
| Family: | Psilotaceae |
| Genus: | Psilotum |
| Species | |
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Psilotum (whisk fern) is a genus of fern-like vascular plants, one of two genera in the family Psilotaceae, order Psilotales, and class Psilotopsida (the other being Tmesipteris). The name of the genus is from Greek psilos = naked, because it lacks organs, such as leaves, normally found in other ferns.
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[edit] Species and distribution
There are two species, Psilotum nudum and Psilotum complanatum, with a hybrid between them known, Psilotum × intermedium W. H. Wagner.
The distribution of Psilotum is tropical and subtropical, in the New World, Asia, and the Pacific, with a few isolated populations in SW Europe. The highest latitudes known are in South Carolina, Cádiz province in Spain,[1] and southern Japan for P. nudum. In the U.S., one species is found from Florida to Texas, the other in Hawaii.
[edit] 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[2] strongly confirms that Psilotum is a fern. Psilophytes are sister to ophioglossoid ferns.
[edit] Gametophyte
The gametophyte of Psilotum nudum L. Beauv. (P. triquetrum Swartz) is unusual in that it branches dichotomously, lives underground and possesses vascular tissue.[3] The nutrition of the gametophyte appears to be myco-heterotrophic, assisted by endophytic fungi.[4]
[edit] References
- ^ "Psilotum nudum". Atlas y Libro Rojo de la Flora Vascular Amenazada de España. http://www.mma.es/portal/secciones/biodiversidad/inventarios/inb/flora_vascular/pdf/1066.pdf.
- ^ Qiu, Y-L and Palmer, J (1999) "Phylogeny of early land plants: insights from genes and genomes." Trends in Plant Science 4(1), 26-30
- ^ Holloway, J.E. (1939) The gametophyte, embryo and young rhizome of Psilotum triquetrum Schwarz. Annals of Botany 3, 313-336
- ^ Manton, I. (1942) A note on the cytology of Psilotum with special reference to vascular prothalli from Rangitoto Is. Annals of Botany 6 283-92
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