Psilotaceae is a family of
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 ...
s (class Polypodiopsida) consisting of two genera, ''
Psilotum'' and ''
Tmesipteris'' with about a dozen species.
It is the only family in the
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Psilotales.
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Description
Once thought to be descendants of early vascular plants (the Psilophyta of the Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...
period), Psilotaceae have been shown by molecular phylogenetics to be ferns ( Polypodiopsida), and a sister group of the Ophioglossaceae. The family contains two genera, '' Psilotum'' and '' Tmesipteris''. The first genus, ''Psilotum'', consists of small shrubby plants of the dry tropics commonly known as "whisk ferns". The other genus, ''Tmesipteris'', is an epiphyte found in Australia, New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...
, and New Caledonia.
All members of Psilotaceae are vascular plant
Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...
s without any true roots. Rather, the plants are anchored by an underground system of rhizomes. The small, stem-like 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 ...
s of Psilotaceae are located in this rhizome system, and they aid in a plant's nutrient absorption through the soil. This is primarily achieved through saprotrophic feeding on organic soil matter and mycorrhizal interactions.
Psilotaceae do not have leaves. Some species have leaf-like structures called enations which have no vascular tissue except for a small bundle at the base. These are almost peg-like, stubby and are generally not considered true leaves, though they likely evolved from them. Members of '' Tmesipteris'' may appear to have leaves, but these are really phylloclades, or flattened stems.
The sporangia of Psilotaceae are fused together into small and distinctive yellow balls called synangia (shown in the picture of ''P. nudum'' above). These synangia are located off the stems of the plants. They contain two sporangia each in ''Tmesipteris'' species, and three sporangia each in ''Psilotum'' species. A thick tapetum nourishes the developing 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, ...
s, as is typical of eusporangiate ferns like Psilotaceae.
Classification
In the molecular phylogenetic classification of Smith et al. in 2006, Psilotales, containing the single family Psilotaceae comprising ''Psilotum'' and ''Tmesipteris'', was placed with the order Ophioglossales in the class Psilotopsida.
References
External links
Introduction to the Psilotales
{{Taxonbar, from=Q500230
Fern families