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 t ...

s (class Polypodiopsida) consisting of two genera, ''

Psilotum ''Psilotum'' is a genus of fern-like vascular plants. It is one of two genera in the family Psilotaceae commonly known as whisk ferns, the other being ''Tmesipteris''. Plants in these two genera were once thought to be descended from the earlies ...

'' and ''

Tmesipteris ''Tmesipteris'', the hanging fork ferns, is a genus of ferns, one of two genera in the family Psilotaceae, order Psilotales (the other being ''Psilotum''). ''Tmesipteris'' is restricted to certain lands in the Southern Pacific, notably Australia ...

'' with about a dozen species. It is the only family in the order Psilotales.

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, whe ...

period), Psilotaceae have been shown by molecular phylogenetics to be ferns (

Polypodiopsida 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 exce ...

), and a sister group of the Ophioglossaceae. The family contains two genera, ''

'' and ''

''. 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 Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

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 smaller islands. It is the sixth-largest island count ...

, and

New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...

. 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 al ...

s without any true roots. Rather, the plants are anchored by an underground system of

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

s. 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 Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ( ...

feeding on organic soil matter and

mycorrhiza A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant ...

l interactions. Psilotaceae do not have leaves. Some species have leaf-like structures called

enations Enations are scaly leaflike structures, differing from leaves in their lack of vascular tissue. They are created by some leaf diseases and occur normally on ''Psilotum''. Enations are also found on some early plants such as ''Rhynia'', where the ...

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 ''

'' may appear to have leaves, but these are really phylloclades, or flattened stems. The

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cyc ...

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, f ...

s, as is typical of

eusporangiate fern Eusporangiate ferns are vascular spore plants, whose sporangia arise from several epidermal cells and not from a single cell as in leptosporangiate ferns. Typically these ferns have reduced root systems and sporangia that produce large amounts o ...

s 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 Ophioglossaceae, the adder's-tongue family, is a small family of ferns. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is the only family in the order Ophioglossales, which together with the Psilotales is placed in the su ...

in the class

Psilotopsida Ophioglossidae is one of the four subclasses of Polypodiopsida (ferns). This subclass consists of the ferns commonly known as whisk ferns, grape ferns, adder's-tongues and moonworts. It is equivalent to the class Psilotopsida in previous treat ...

. The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009) which placed all land plants in Equisetopsida, made it a member of subclass

Ophioglossidae Ophioglossidae is one of the four subclasses of Polypodiopsida (ferns). This subclass consists of the ferns commonly known as whisk ferns, grape ferns, adder's-tongues and moonworts. It is equivalent to the class Psilotopsida in previous treatm ...

, equivalent to Smith's Psilotopsida. The placement of Psilotales in subclass Ophioglossidae has subsequently been followed in the classifications of Christenhusz and Chase (2014) and PPG I (2016). In the past ''Tmesipteris'' has been placed in its own family, Tmesipteridaceae, but this has not been maintained in the system of Smith et al. and later classifications.

References

External links

Introduction to the Psilotales
{{Taxonbar, from=Q500230 Fern families