Pteridophyte
Encyclopedia
The pteridophytes are vascular plant
s (plants with xylem
and phloem
) that produce neither flower
s nor seed
s, and are hence called vascular cryptogams. Instead, they reproduce and disperse
only via spore
s. Pteridophytes include horsetail
s, fern
s, club mosses, and quillwort
s. They are used for medicinal purposes, as soil -binders
, and are frequently planted as ornamentals
.
In addition to these living groups of pteridophytes are several groups now extinct and known only from fossil
s. These groups include the Rhyniophyta, Zosterophyllophyta, Trimerophytophyta, and the progymnosperm
s.
Modern studies of the land plants agree that all the pteridophytes share a single common ancestor. However, they are not a clade
(monophyletic group) because the seed plants are also descended from within this group—probably close relatives of the progymnosperms.
-oriented; that is, the normal plant is the diploid sporophyte, with the only haploid structure being the gametophyte
(prothallium
) in season. This basic pattern is like that found in the seed plants but with an important exception. Unlike the seed plants, the pteridophytes have a gametophyte stage that is free-living. As a result, pteridophyte sexuality is more complicated than that of the seed plants. There are several basic categories of sexuality in pteridophytes. The terms distinguish between types of gametophyte sexuality:
Notice that these terms are not the same as monoecious and dioecious, which refer to whether or not a sporophyte
plant bears one or both kinds of gametophyte. Those terms apply only to seed plants
.
Vascular plant
Vascular 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 (plants with xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
and phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
) that produce neither flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s nor seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s, and are hence called vascular cryptogams. Instead, they reproduce and disperse
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
only via spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s. Pteridophytes include horsetail
Horsetail
Equisetum is the only living genus in the Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.Equisetum is a "living fossil", as it is the only living genus of the entire class Equisetopsida, which for over one hundred million years was much more diverse and...
s, fern
Fern
A 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...
s, club mosses, and quillwort
Quillwort
Isoëtes, also written Isoetes and commonly known as the quillworts, is a genus of plants in the class Isoetopsida and order Isoetales. They are considered "fern allies". There are about 140-150 species, with a cosmopolitan distribution but often scarce to rare...
s. They are used for medicinal purposes, as soil -binders
Erosion control
Erosion control is the practice of preventing or controlling wind or water erosion in agriculture, land development and construction. Effective erosion controls are important techniques in preventing water pollution and soil loss.-Introduction:...
, and are frequently planted as ornamentals
Ornamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
.
Pteridophyte classification
They do not form a monophyletic group but consist of two groups:- the LycopodiophytaLycopodiophytaThe Division Lycopodiophyta is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant vascular plant division at around 410 million years old, and includes some of the most "primitive" extant species...
(club mosses, spike mosses, and quillworts), - FernFernA 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...
s:- Marattioid ferns,
- Equisetophyta (horsetails),
- Psilotophyta (whisk ferns) and Ophioglossophyta (adder's tongues and grape ferns),
- Leptosporangiate fernLeptosporangiate fernLeptosporangiate ferns are the largest group of living ferns. They are often considered to be the class Pteridopsida or Polypodiopsida, although other classifications assign them a different rank...
s (the largest group of ferns).
In addition to these living groups of pteridophytes are several groups now extinct and known only from fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s. These groups include the Rhyniophyta, Zosterophyllophyta, Trimerophytophyta, and the progymnosperm
Progymnosperm
The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the "trimerophytes", and eventually gave rise to the gymnosperms. They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida...
s.
Modern studies of the land plants agree that all the pteridophytes share a single common ancestor. However, they are not a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
(monophyletic group) because the seed plants are also descended from within this group—probably close relatives of the progymnosperms.
Pteridophyte sexuality
These plants are generally sporophyteSporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
-oriented; that is, the normal plant is the diploid sporophyte, with the only haploid structure being the gametophyte
Gametophyte
A 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....
(prothallium
Prothallium
A prothallium, or prothallus is usually the gametophyte stage in the life of a fern or other pteridophyte, i.e. a spore-bearing plant with vascular tissue...
) in season. This basic pattern is like that found in the seed plants but with an important exception. Unlike the seed plants, the pteridophytes have a gametophyte stage that is free-living. As a result, pteridophyte sexuality is more complicated than that of the seed plants. There are several basic categories of sexuality in pteridophytes. The terms distinguish between types of gametophyte sexuality:
- Dioicous pteridophytes produce only antheridiaAntheridiumAn antheridium or antherida is a haploid structure or organ producing and containing male gametes . It is present in the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes...
(male organs) or archegoniaArchegoniumAn archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
(female organ) on a single gametophyte body. - MonoicousMonoicousMonoicous is a botanical term used to describe plants which bear both sperm and eggs on the same gametophyte. Dioicous is the complementary term describing species in which gametophytes produce only sperm or eggs but never both. The terms are used largely but not exclusively in the context of...
pteridophytes produce both antheridiaAntheridiumAn antheridium or antherida is a haploid structure or organ producing and containing male gametes . It is present in the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes...
and archegoniaArchegoniumAn archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
on the same gametophyte body.- Protandrous pteridophytes produce the male antheridia first, and then their female archegonia.
- Protogynous pteridophytes produce the archegonia first, followed by the antheridia.
Notice that these terms are not the same as monoecious and dioecious, which refer to whether or not a sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
plant bears one or both kinds of gametophyte. Those terms apply only to seed plants
Spermatophyte
The spermatophytes comprise those plants that produce seeds. They are a subset of the embryophytes or land plants...
.