The mosses are non-vascular land plants belonging to the Bryophyta division of the Embryophyta superdivision of the kingdom Plantae. The term "Bryophyta sensu stricto”Is used to refer exclusively to mosses, which share the division with other similar plants.
With more than 23,000 described species, the Bryophyta division (sensu lato, that is, in a broad sense) includes both mosses (Bryophyta sensu stricto) as well as liverworts (Marchantiophyta) and hornworts (Anthocerophyta) and corresponds to a group of "lower" land plants.
Mosses (bryophytes) make up the second most diverse phylum of all land plants, as nearly 13,000 species have been described for this group alone (there are probably many more that have not yet been described).
Phylogenetically speaking, it has been argued that bryophytes are the "key" group for understanding the phylogenetic relationships between current "higher" land plants and how the closest ancestors were "able" to leave aquatic environments and "conquer" the mainland.
Since the end of the last century, mosses have been "used" as bioindicators of air pollution. In addition, its capacity to absorb and retain water is essential not only for the establishment of forests and other ecosystems, but also for the maintenance of river basins and wetlands..
These tiny non-vascular plants have a special function in the global carbon cycle, since in many ecosystems they are an important source of storage of this mineral, since they represent high percentages of plant biomass.
Article index
Mosses, as well as liverworts and hornworts, have a diplobionic haplo life cycle that “marks” the change from the haploid-dominant life cycle of algae to the sporophyte-dominated life cycle, observed in vascular plants..
A haplo diplobionic life cycle is one by which haploid gametes develop into a multicellular structure known as a haploid gametophyte (n) and where fertilization gives rise to a diploid multicellular sporophyte (2n) that produces haploid spores by meiosis.
In bryophytes, the gametophyte is free-living and is an autotrophic (photosynthetic) foliose structure. After fertilization, the sporophyte develops, which has the appearance of an unbranched axis in whose terminal portion there is a capsule containing spores.
The sporophyte in bryophytes is partially dependent on the gametophyte for survival, which means that it is not entirely independent of it..
The vegetative body of bryophytes, that is, the one we see in forests or growing on wet rocks, corresponds to the gametophyte, which is the dominant phase of their life cycle (the haploid phase).
The gametophyte, as mentioned above, is a multicellular body that is responsible for developing the sexual organs known as gametangia. This structure grows apically thanks to the divisions suffered by a set of cells at its apex.
The gametophyte can be considered "divided" into sections that we call metamers, which are assembled into "modules", from which branching systems can be formed..
Macroscopically we say that the vegetative body of a moss is divided into:
Rhizoids are very thin filaments that work to anchor the gametophyte to the substrate where it grows and that may be involved in the conduction of water (they are analogous to roots, but with a simpler architecture).
Many scientific texts state that the multicellular rhizoids of mosses are thigmotropic, which is why they bind strongly to solid objects in their path. These rhizoids arise from cells in the epidermis at the base of the stem, as well as in the ventral portion of the stems and branches..
The stems (caudilios) are the vegetative axes that have a fairly simple architecture: a layer of epidermal cells that surrounds a “cortex” made up of parenchymal cells, which can surround a set of central cells that can function in the conduction of water..
These structures are responsible for supporting the leaves, also called filidia, which, unlike the leaves of vascular or "superior" plants, do not have a petiole and are inserted into the stems along their entire base..
The leaves develop from primordia in each metamer of the stem and their arrangement in this (phyllotaxis) depends on the spatial arrangement of these metamers (they are often arranged in a spiral shape, which maximizes light interception).
Mosses grow in a "creeping" way. They are small plants and have the ability to cover large areas of land, forming a kind of green "carpet" or "mattress" with great water retention capacity, which makes them vital for the maintenance of many ecosystems..
Many algae, lichens and vascular plants are constantly confused with bryophytes, which is why their common names often include the term "moss", mistakenly coined.
The true mosses, viz. The Bryophyta sensu stricto represent a cutting edge composed of 5 classes:
- Sphagnopsida (the "peat" mosses)
- Takakiopsida
- Andreaeopsida (the "granite" mosses)
- Tetraphidopsida
- Bryopsida (the "true" mosses)
The classes Takakiopsida and Tetraphidopsida are very small, the first composed of a single order and a genus and the second composed of a single order and two genera; so the main attention is always directed towards the other three classes.
In this class, also known as the “true moss” class, there are more than 10,000 species of mosses, representing more than 90% of all species in the group (new species are constantly being described).
They are relatively small plants (from 0.5 millimeters to 50 centimeters), with folious gametophytic phases (of leaves the thickness of a single cell layer) and multicellular rhizoids..
Mosses of this class, also known as "peat mosses" are very popular in horticulture, as they have an amazing capacity to hold water..
In this class 2 genres have been described:
- Sphagnum: Approximately 400 species, present in humid and swampy regions of the northern hemisphere and distinguishable by the red capsules of their sporophytes.
- Ambuchanania: only found on the island of Tasmania on small "spots" of wet sand.
The "granite mosses" comprise the class Andreaeopsida, which is made up of two genera: Andreaea Y Andreaeobryum.
The gender Andreaea it has more or less 100 species. They are very small, black-green or reddish-brown mosses that are mainly present in mountainous regions of the Arctic, often on granite rocks (hence their common name)..
Andreaeobryum is a genus composed of a single species and its distribution is restricted to northeast Canada, very close to Alaska, growing on rocks or calcareous stones.
Most moss species grow in humid habitats, both in temperate and tropical forests, frequently associated with wetlands and streams (there are some semi-aquatic and aquatic species).
In these environments, many expert researchers in the field are of the opinion that mosses can become so dominant in certain areas that they exclude other plants, that is, they make it impossible to settle in the same places..
However, these plants are not restricted to such habitats, as some species have been found in relatively dry deserts, forming large masses on rocks exposed to the sun that, therefore, reach high temperatures..
Mosses also represent the main vegetation on many rocky slopes in mountainous environments and some species survive the low temperatures of the Antarctic continent..
Mosses, then, are present in a large number of niches, both natural and artificial, which can be from sea level to more than 4500 meters above sea level (masl) (they prefer, however, gradients between 1500 and 3500 meters above sea level, as there is more humidity).
They can then grow on soil, decaying matter, wood, stone, drains, pipes and damp walls of almost any material..
Mosses reproduce in two distinct phases: one haploid and one diploid. The haploid phase is known as the gametophyte and is the "dominant phase"; This grows by mitosis and is from which the antheridia and archegonia are formed, male and female reproductive "organs", respectively..
The fertilization of the archegonium (the ovule) by the antheridium (by its sperm or anterozoid cells) depends on environmental conditions, mainly on the availability of water. This process culminates in the formation of the sporophyte, which is the diploid phase..
The sporophyte derived from the ovule + anterozoid fusion ("organ" that carries spores) produces the meiotic spores (by meiosis) in a portion known as the sporangium.
These spores are expelled from the sporangium and germinate on different substrates, forming a new haploid gametophyte that repeats the cycle..
The "sex" of mosses is genetically determined, but the sex organs are genetically determined in response to certain environmental parameters..
As in all land plants, bryophytes' sexual organs are multicellular and provide some protection for gametes, which are reproductive cells (the egg or ovum and motile or anterozoid sperm cells)..
Mosses can be bisexual (monoecious) or unisexual (dioecious), that is, the same plant can have both female and male organs or that one individual is female and another is male, respectively..
Mosses are terrestrial plants, but it is said that they are not vascular since they do not have an internal system of cells that conduct water and elaborate matter (xylem and phloem)..
From the above we understand that nutrients are transported from cell to cell by diffusion or actively (using energy in the form of ATP).
They are, like practically all terrestrial plants, photosynthetic autotrophic organisms, which means that they obtain their food by photosynthesis, that is: they convert the light energy of the sun's rays into chemical energy, using water and CO2 in the process and "discarding ”Oxygen to the environment.
These plants absorb the ions and minerals they need for the synthesis of their cellular compounds and for the maintenance of their internal homeostasis from humid surfaces where they live..
Yet No Comments