Psilotales
From Wikipedia, the free encyclopedia
 |
||||||||
|---|---|---|---|---|---|---|---|---|
 Closeup of Psilotum nudum
|
||||||||
| Scientific classification | ||||||||
|
||||||||
|
|
||||||||
Psilotales is an order (i.e., order) of the Class Psilotopsida. This order contains one family, Psilotaceae, with only two living genera, Psilotum, small shrubby plants of the dry tropics commonly known as "Whisk ferns", and Tmesipteris, an epiphyte found in Australia, New Zealand, and New Caledonia. There has long been controversy about the relationships of the Psilotophyta, with some claiming that they are ferns (Pteridophyta), and others maintaining that they are descendants of the first vascular plants (the Psilophyta of the Devonian period). Recent evidence from DNA demonstrates a much closer relationship to the ferns, and that they are closely related to the Ophioglossales, in particular.
All Psilotales share a few characteristics. Psilotales are vascular plants. They lack leaves, instead having small outgrowths called enations. The enations are not considered true leaves because there is only a vascular bundle just underneath them, but not inside, as in leaves. Psilotales also do not have true roots. They are anchored by rhizoids. Absorption is aided by symbiotic fungi called mycorrhizae.
Three sporangia are united into a synangium, which is considered to be a very reduced series of branches. There is a thick tapetum to nourish the developing spores, as is typical of eusporangiate plants. The gametophyte looks like a small piece of subterranean stem, but produces antheridia and archegonia.
