Moss
Moss | |
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Clumps of moss on the ground and base of trees in the Allegheny National Forest, Pennsylvania, United States | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Embryophytes |
Clade: | Setaphyta |
Division: | Bryophyta sensu stricto
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Classes[2] | |
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Synonyms | |
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Mosses are small,
Mosses are commonly confused with liverworts, hornworts and
The main commercial significance of mosses is as the main constituent of
Physical characteristics
Description
Botanically, mosses are
, and have no flowers.Moss gametophytes have stems which may be simple or branched and upright (acrocarp) or prostrate (pleurocarp). The early divergent classes Takakiopsida, Sphagnopsida, Andreaeopsida and Andreaeobryopsida either lack stomata or have pseudostomata that do not form pores. In the remaining classes, stomata have been lost more than 60 times.[15] Their leaves are simple, usually only a single layer of cells with no internal air spaces, often with thicker midribs (nerves). The nerve can run beyond the edge of the leaf tip, termed excurrent. The tip of the leaf blade can be extended as a hair point, made of colourless cells. These appear white against the dark green of the leaves. The edge of the leaf can be smooth or it may have teeth. There may be a distinct type of cell defining the edge of the leaf, distinct in shape and/or colour from the other leaf cells.[16] Moss has threadlike
Life cycle
Vascular
The moss life-cycle starts with a haploid spore that germinates to produce a protonema (pl. protonemata), which is either a mass of thread-like filaments or thalloid (flat and thallus-like). Massed moss protonemata typically look like a thin green felt, and may grow on damp soil, tree bark, rocks, concrete, or almost any other reasonably stable surface. This is a transitory stage in the life of a moss, but from the protonema grows the gametophore ("gamete-bearer") that is structurally differentiated into stems and leaves. A single mat of protonemata may develop several gametophore shoots, resulting in a clump of moss.
From the tips of the gametophore stems or branches develop the sex organs of the mosses. The female organs are known as
Gametophore tip growth is disrupted by fungal
Mosses can be either
After fertilisation, the immature sporophyte pushes its way out of the archegonial venter. It takes several months for the
Most mosses rely on the wind to disperse the spores. In the genus Sphagnum the spores are projected about 10–20 cm (4–8 in) off the ground by compressed air contained in the capsules; the spores are accelerated to about 36,000 times the earth's gravitational acceleration g.[23][24]
It has recently been found that microarthropods, such as
In many mosses, e.g., Ulota phyllantha, green vegetative structures called gemmae are produced on leaves or branches, which can break off and form new plants without the need to go through the cycle of fertilization. This is a means of asexual reproduction, and the genetically identical units can lead to the formation of clonal populations.
Dwarf males
Moss dwarf males (also known as nannandry or phyllodioicy) originate from wind-dispersed male spores that settle and germinate on the female shoot where their growth is restricted to a few millimeters. In some species, dwarfness is genetically determined, in that all male spores become dwarf.[28] More often, it is environmentally determined in that male spores that land on a female become dwarf, while those that land elsewhere develop into large, female-sized males.[28][29][30][31] In the latter case, dwarf males that are transplanted from females to another substrate develop into large shoots, suggesting that the females emit a substance which inhibits the growth of germinating males and possibly also quickens their onset of sexual maturation.[30][31] The nature of such a substance is unknown, but the phytohormone auxin may be involved[28]
Having the males growing as dwarfs on the female is expected to increase the
Dwarf males occur in several unrelated
DNA repair
The moss
Classification
More recently, mosses have been grouped with the
The mosses, (Bryophyta sensu stricto), are divided into eight classes:
division Bryophyta
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The current phylogeny and composition of the Bryophyta.[2][48] |
Six of the eight classes contain only one or two genera each. Polytrichopsida includes 23 genera, and Bryopsida includes the majority of moss diversity with over 95% of moss species belonging to this class.
The Sphagnopsida, the peat-mosses, comprise the two living genera Ambuchanania and Sphagnum, as well as fossil taxa. Sphagnum is a diverse, widespread, and economically important one. These large mosses form extensive acidic bogs in peat swamps. The leaves of Sphagnum have large dead cells alternating with living photosynthetic cells. The dead cells help to store water. Aside from this character, the unique branching, thallose (flat and expanded) protonema, and explosively rupturing sporangium place it apart from other mosses.
Andreaeopsida and Andreaeobryopsida are distinguished by the biseriate (two rows of cells) rhizoids, multiseriate (many rows of cells) protonema, and sporangium that splits along longitudinal lines. Most mosses have capsules that open at the top.
Polytrichopsida have leaves with sets of parallel lamellae, flaps of chloroplast-containing cells that look like the fins on a heat sink. These carry out photosynthesis and may help to conserve moisture by partially enclosing the gas exchange surfaces. The Polytrichopsida differ from other mosses in other details of their development and anatomy too, and can also become larger than most other mosses, with e.g., Polytrichum commune forming cushions up to 40 cm (16 in) high. The tallest land moss, a member of the Polytrichidae is probably Dawsonia superba, a native to New Zealand and other parts of Australasia.
Geological history
The fossil record of moss is sparse, due to their soft-walled and fragile nature. Unambiguous moss fossils have been recovered from as early as the
Recent research shows that ancient moss could explain why the Ordovician ice ages occurred. When the ancestors of today's moss started to spread on land 470 million years ago, they absorbed CO2 from the atmosphere and extracted minerals by secreting organic acids that dissolved the rocks they were growing on. These chemically altered rocks in turn reacted with the atmospheric CO2 and formed new carbonate rocks in the ocean through the weathering of calcium and magnesium ions from silicate rocks. The weathered rocks also released significant amounts of phosphorus and iron which ended up in the oceans, where it caused massive algal blooms, resulting in organic carbon burial, extracting more carbon dioxide from the atmosphere. Small organisms feeding on the nutrients created large areas without oxygen, which caused a mass extinction of marine species, while the levels of CO2 dropped all over the world, allowing the formation of ice caps on the poles.[52][53]
Ecology
Habitat
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Dense moss colonies in a cool coastal forest
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A cool high altitude/latitude moss forest; the forest floor is covered in moss, beneath conifers
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Moss growing alongbasalticrock, Iceland.
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Moss growing along the stream from a karst spring; travertine deposits from the stream water and the moss overgrows it, forming this ridge, with the stream on top.
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Moss with sporophytes on brick
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Young sporophytes of the common moss Tortula muralis (wall screw-moss)
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Retaining wall covered in moss
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A small clump of moss beneath a conifer (a shady, usually dry place)
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Moss on a concrete wall
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Moss (Bryophyta) on the forest floor in Broken Bow, Oklahoma
Moss gametophytes are autotrophic and require sunlight to perform photosynthesis.[54] Shade tolerance varies by species, just as it does with higher plants. In most areas, mosses grow chiefly in moist, shaded areas, such as wooded areas and at the edges of streams, but they can grow anywhere in cool, humid, cloudy climates, and some species are adapted to sunny, seasonally dry areas like alpine rocks or stabilized sand dunes.
Choice of substrate varies by species as well. Moss species can be classed as growing on: rocks, exposed mineral soil, disturbed soils, acid soil, calcareous soil, cliff seeps and waterfall spray areas, streamsides, shaded
Mosses are also found in cracks between paving stones in damp city streets, and on roofs. Some species adapted to disturbed, sunny areas are well adapted to urban conditions and are commonly found in cities. Examples would be Rhytidiadelphus squarrosus, a garden weed in Vancouver and Seattle areas; Bryum argenteum, the cosmopolitan sidewalk moss, and Ceratodon purpureus, red roof moss, another cosmopolitan species. A few species are wholly aquatic, such as Fontinalis antipyretica, common water moss; and others such as Sphagnum inhabit bogs, marshes and very slow-moving waterways.[12] Such aquatic or semi-aquatic mosses can greatly exceed the normal range of lengths seen in terrestrial mosses. Individual plants 20–30 cm (8–12 in) or more long are common in Sphagnum species for example. But even aquatic species of moss and other bryophytes needs their mature capsules to be exposed to air by seta elongation or seasonal lowering of water level to be able to reproduce.[55]
Wherever they occur, mosses require liquid water for at least part of the year to complete fertilisation. Many mosses can survive desiccation, sometimes for months, returning to life within a few hours of rehydration.[54]
It is generally believed that in the Northern Hemisphere, the north side of trees and rocks will generally have more luxuriant moss growth on average than other sides.[56] The reason is assumed to be because sunshine on the south side causes a dry environment. The reverse would be true in the Southern Hemisphere. Some naturalists feel that mosses grow on the damper side of trees and rocks.[11] In some cases, such as sunny climates in temperate northern latitudes, this will be the shaded north side of the tree or rock. On steep slopes, it may be the uphill side. For mosses that grow on tree branches, this is generally the upper side of the branch on horizontally growing sections or near the crotch. In cool, humid, cloudy climates, all sides of tree trunks and rocks may be equally moist enough for moss growth. Each species of moss requires certain amounts of moisture and sunlight and thus will grow on certain sections of the same tree or rock.
Some mosses grow underwater, or completely waterlogged. Many prefer well-drained locations. There are mosses that preferentially grow on rocks and tree trunks of various chemistries.[57]
Relationship with cyanobacteria
In boreal forests, some species of moss play an important role in providing nitrogen for the ecosystem due to their relationship with nitrogen-fixing cyanobacteria. Cyanobacteria colonize moss and receive shelter in return for providing fixed nitrogen. Moss releases the fixed nitrogen, along with other nutrients, into the soil "upon disturbances like drying-rewetting and fire events", making it available throughout the ecosystem.[58]
Cultivation
Moss is often considered a weed in grass lawns, but is deliberately encouraged to grow under aesthetic principles exemplified by Japanese gardening. In old temple gardens, moss can carpet a forest scene. Moss is thought to add a sense of calm, age, and stillness to a garden scene. Moss is also used in bonsai to cover the soil and enhance the impression of age.[59] Rules of cultivation are not widely established. Moss collections are quite often begun using samples transplanted from the wild in a water-retaining bag. Some species of moss can be extremely difficult to maintain away from their natural sites with their unique requirements of combinations of light, humidity, substrate chemistry, shelter from wind, etc.
Growing moss from spores is even less controlled. Moss spores fall in a constant rain on exposed surfaces; those surfaces which are hospitable to a certain species of moss will typically be colonised by that moss within a few years of exposure to wind and rain. Materials which are porous and moisture retentive, such as brick, wood, and certain coarse concrete mixtures, are hospitable to moss. Surfaces can also be prepared with acidic substances, including buttermilk, yogurt, urine, and gently puréed mixtures of moss samples, water and ericaceous compost.
In the cool, humid, cloudy Pacific Northwest, moss is sometimes allowed to grow naturally as a moss lawn, one that needs little or no mowing, fertilizing or watering. In this case, grass is considered to be the weed.[60] Landscapers in the Seattle area sometimes collect boulders and downed logs growing mosses for installation in gardens and landscapes. Woodland gardens in many parts of the world can include a carpet of natural mosses.[54] The Bloedel Reserve on Bainbridge Island, Washington State, is famous for its moss garden. The moss garden was created by removing shrubby underbrush and herbaceous groundcovers, thinning trees, and allowing mosses to fill in naturally.[61]
Green roofs and walls
Mosses are sometimes used in green roofs. Advantages of mosses over higher plants in green roofs include reduced weight loads, increased water absorption, no fertilizer requirements, and high drought tolerance. Since mosses do not have true roots, they require less planting medium than higher plants with extensive root systems. With proper species selection for the local climate, mosses in green roofs require no irrigation once established and are low maintenance.[62] Mosses are also used on green walls.
Mossery
A passing fad for moss-collecting in the late 19th century led to the establishment of mosseries in many British and American gardens. The mossery is typically constructed out of slatted wood, with a flat roof, open to the north side (maintaining shade). Samples of moss were installed in the cracks between wood slats. The whole mossery would then be regularly moistened to maintain growth.
Aquascaping
Aquascaping uses many aquatic mosses. They do best at low nutrient, light, and heat levels, and propagate fairly readily. They help maintain a water chemistry suitable for aquarium fish.[63] They grow more slowly than many aquarium plants, and are fairly hardy.[64]
Growth inhibition
Moss can be a troublesome weed in containerized nursery operations and greenhouses.[65] Vigorous moss growth can inhibit seedling emergence and penetration of water and fertilizer to the plant roots.
Moss growth can be inhibited by a number of methods:
- Decreasing availability of water through drainage.
- Increasing direct sunlight.
- Increasing number and resources available for competitive plants like grasses.
- Increasing the lime.
- Heavy traffic or manually disturbing the moss bed with a rake
- Application of chemicals such as ferrous sulfate(e.g., in lawns) or bleach (e.g., on solid surfaces).
- In containerized nursery operations, coarse mineral materials such as sand, gravel, and rock chips are used as a fast-draining top dressing in plant containers to discourage moss growth.
The application of products containing ferrous sulfate or
Uses
Traditional
Preindustrial societies made use of the mosses growing in their areas.
The capacity of dried mosses to absorb fluids has made their use practical in both medical and culinary uses. North American tribal people used mosses for diapers, wound dressing, and menstrual fluid absorption.[54] Tribes of the Pacific Northwest in the United States and Canada used mosses to clean salmon prior to drying it, and packed wet moss into pit ovens for steaming camas bulbs. Food storage baskets and boiling baskets were also packed with mosses.[54]
Recent research investigating the Neanderthals remains recovered from El Sidrón have provided evidence that their diet would have consisted primarily of pine nuts, moss and mushrooms. This is contrasted by evidence from other European locations which point to a more carnivorous diet.[67]
In
Commercial
There is a substantial market in mosses gathered from the wild. The uses for intact moss are principally in the florist trade and for home decoration. Decaying moss in the genus Sphagnum is also the major component of peat, which is "mined" for use as a fuel, as a horticultural soil additive, and in smoking malt in the production of Scotch whisky.
Sphagnum moss, generally the species S. cristatum and S. subnitens, is harvested while still growing and is dried out to be used in nurseries and horticulture as a plant growing medium.
Some Sphagnum mosses can absorb up to 20 times their own weight in water.[69] In World War I, Sphagnum mosses were used as first-aid dressings on soldiers' wounds, as these mosses said to absorb liquids three times faster than cotton, retain liquids better, better distribute liquids uniformly throughout themselves, and are cooler, softer, and be less irritating.[69] It is also claimed to have antibacterial properties.[70] Native Americans were one of the peoples to use Sphagnum for diapers and menstrual pads, which is still done in Canada.[71]
In rural UK, Fontinalis antipyretica was traditionally used to extinguish fires as it could be found in substantial quantities in slow-moving rivers and the moss retained large volumes of water which helped extinguish the flames. This historical use is reflected in its specific Latin/Greek name, the approximate meaning of which is "against fire".
In Mexico, moss is used as a Christmas decoration.
London installed several structures called "City Trees": moss-filled walls, each of which is claimed to have "the air-cleaning capability of 275 regular trees" by consuming nitrogen oxides and other types of air pollution and producing oxygen.[74]
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Further reading
- ISBN 0-87071-499-6.