Bryophyte
Overview
Bryophyte is a traditional name used to refer to all embryophyte
Embryophyte
The land plants or embryophytes, more formally Embryophyta or Metaphyta, are the most familiar group of plants. They are called 'land plants' because they live primarily in terrestrial habitats, in contrast with the related green algae that are primarily aquatic. The embryophytes include trees,...

s (land plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s) that do not have true vascular tissue
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...

 and are therefore called 'non-vascular plant
Non-vascular plant
Non-vascular plants is a general term for those plants without a vascular system . Although non-vascular plants lack these particular tissues, a number of non-vascular plants possess tissues specialized for internal transport of water....

s'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...

, they are not considered to be true vascular tissue. Currently bryophytes are thought not to be a natural or monophyletic group; however the name is convenient and remains in use as a collective term.
Encyclopedia
Bryophyte is a traditional name used to refer to all embryophyte
Embryophyte
The land plants or embryophytes, more formally Embryophyta or Metaphyta, are the most familiar group of plants. They are called 'land plants' because they live primarily in terrestrial habitats, in contrast with the related green algae that are primarily aquatic. The embryophytes include trees,...

s (land plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s) that do not have true vascular tissue
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...

 and are therefore called 'non-vascular plant
Non-vascular plant
Non-vascular plants is a general term for those plants without a vascular system . Although non-vascular plants lack these particular tissues, a number of non-vascular plants possess tissues specialized for internal transport of water....

s'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...

, they are not considered to be true vascular tissue. Currently bryophytes are thought not to be a natural or monophyletic group; however the name is convenient and remains in use as a collective term. Bryophytes produce enclosed reproductive structures (gametangia and sporangia), but they produce neither flowers 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, reproducing 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. The term bryophyte comes from Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 βρύον - bryon, "tree-moss, oyster-green" + φυτόν - fyton "plant".

Bryophyte classification and phylogeny

Traditionally, all living land plants without vascular tissues were classified in a single taxonomic group, often a division
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

 (or phylum). More recently, phylogenetic research has questioned whether the bryophytes form a monophyletic group and thus whether they should form a single taxon. A broad consensus among systematists has recently emerged that bryophytes as a whole are not a natural group (i.e. are paraphyletic), although each of the three extant (living) groups is monophyletic. The three lineages are Marchantiophyta
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....

 (liverworts), Bryophyta
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...

 (mosses) and Anthocerotophyta (hornworts).

The vascular plant
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 or tracheophytes are the fourth lineage of living land plants. Currently there is some uncertainty over the exact evolutionary relationships among these four lineages, although this may be nearing resolution as data on a variety of coding and non-coding DNA sequences from all three genomes (chloroplast, mitochondrion and nucleus) in addition to protein sequences are brought to bear on the problem. Although a 2005 study supported the traditional view that the bryophytes form a monophyletic group, the preponderance of currently available evidence suggests that the hornworts are sister to vascular plants and liverworts are sister to all other land plants, as shown in the cladogram below.
When extinct plants are taken into account, the picture is slightly altered. There are extinct land plants, such as the horneophytes, which are not bryophytes, but also are not vascular plants since like bryophytes they do not have true vascular tissue. A different distinction is needed. In bryophytes, the 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...

 is a simple unbranched structure with a single spore-forming organ (sporangium
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...

). In all other land plants, the polysporangiophyte
Polysporangiophyte
Polysporangiophytes, also called polysporangiates or more formally Polysporangiophyta, are plants in which the spore-bearing generation has a structure of branching stems terminating in sporangia...

s, the sporophyte is branched and carries many sporangia. It has been argued that this contrast between bryophytes and other land plants is less misleading than the traditional one of non-vascular versus vascular plant, since many mosses have well-developed water-conducting vessels. The contrast is shown in a slightly different cladogram:
The term "bryophyte" thus refers to a grade of lineages defined primarily by what they lack: compared to other living land plants, they lack vascular tissue containing lignin; compared to all other land plants, they lack branched sporophytes bearing multiple sporangia. The prominence of the gametophyte in the life cycle is also a shared feature of the three bryophyte lineages (extant vascular plants are all sporophyte dominant).

Bryophyte life cycle

Like all land plants (embryophytes), bryophytes show 'alternation of generations
Alternation of generations
Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...

'. A haploid 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....

, each of whose cells contains a fixed number of unpaired chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

s, gives rise to a diploid 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...

, each of whose cells contains twice the number of paired chromosomes. Gametophytes produce sperm and eggs which fuse and grow into sporophytes. Sporophytes produce spores which grow into gametophytes.

Bryophytes are gametophyte dominant, meaning that the more prominent, longer-lived plant is the haploid gametophyte. The diploid sporophytes appear only occasionally and typically remain attached to and nutritionally dependent on the gametophyte. They produce a single sporangium
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...

 (spore producing structure), with, in many cases, a complex capsule aiding in dispersal of the spores.

Liverworts, mosses and hornworts spend most of their lives as gametophytes. Archegonia and antheridia are produced on the gametophytes. These are sometimes at the tips of shoots, in the axils of leaves or hidden under thalli. Some bryophytes create elaborate structures that bear gametangia called gametangiophores. Sperm are flagellated and must swim from antheridia to archegonia. Arthropods may assist in transfer of sperm. Fertilized eggs become zygotes, which develop into sporophyte embryos inside the archegonia. Mature sporophytes do not branch and remain attached to the gametophyte. They consist of a stalk called a seta and a capsule enclosing a single sporangium. Inside the sporangium, spores are produced by meiosis. These are dispersed presumably by wind and if they land in a suitable environment can develop into a new gametophyte. Thus bryophytes disperse by a combination of swimming sperm and spores, in a manner similar to lycophytes and 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.

Bryophyte sexuality

Individual liverwort, moss and hornwort plants can be unisexual or bisexual. The terms for this are as follows:
  • Dioicous bryophytes produce only antheridia
    Antheridium
    An 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...

     (sperm producing structures) or archegonia
    Archegonium
    An 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...

     (egg producing structures) on a single plant body.
  • Monoicous
    Monoicous
    Monoicous 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...

     bryophytes produce both antheridia
    Antheridium
    An 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 archegonia
    Archegonium
    An 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 plant body.


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 megasporangia, microsporangia or both. Those terms generally apply only to seed plants
Spermatophyte
The spermatophytes comprise those plants that produce seeds. They are a subset of the embryophytes or land plants...

.

Some bryophyte species may be either monoicous or dioicous depending on environmental conditions. Other species are exclusively unisexual or bisexual.

See also

  • Embryophyte
    Embryophyte
    The land plants or embryophytes, more formally Embryophyta or Metaphyta, are the most familiar group of plants. They are called 'land plants' because they live primarily in terrestrial habitats, in contrast with the related green algae that are primarily aquatic. The embryophytes include trees,...

  • Marchantiophyta
    Marchantiophyta
    The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....

     (liverworts)
  • Anthocerotophyta
    Hornwort
    Hornworts are a group of bryophytes, or non-vascular plants, comprising the division Anthocerotophyta. The common name refers to the elongated horn-like structure, which is the sporophyte. The flattened, green plant body of a hornwort is the gametophyte plant.Hornworts may be found worldwide,...

     (hornworts)
  • Bryophyta
    Moss
    Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...

     (mosses)
  • Plant sexuality
    Plant sexuality
    Plant sexuality covers the wide variety of sexual reproduction systems found across the plant kingdom. This article describes morphological aspects of sexual reproduction of plants....


External links

  • Glime, Janice M., 2007. Bryophyte Ecology, Volume 1. Physiological Ecology. Ebook sponsored by Michigan Technological University and the International Association of Bryologists.
  • Andrew's Moss Site Photos of bryophytes



The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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