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Moss

2007 Schools Wikipedia Selection. Related subjects: Plants

                              iMoss
   "Muscinae" from Ernst Haeckel's Kunstformen der Natur, 1904
   "Muscinae" from Ernst Haeckel's Kunstformen der Natur, 1904
                    Scientific classification

   Kingdom:  Plantae
   Division: Bryophyta
   Class:    Bryopsida

                                 Subclasses

     * Sphagnidae
     * Andreaeidae
     * Tetraphidae
     * Polytrichidae
     * Archidiidae
     * Buxbaumiidae
     * Bryidae

   Mosses are small, soft plants that are typically 1-10  cm tall,
   occasionally more. 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. At certain times mosses
   produces spore capsules which may appear as beak-like capsules borne
   aloft on thin stalks.

Life cycle

   Most kinds of plants have a double portion of chromosomes in their
   cells ( diploid, i.e. each chromosome exists with a partner that
   contains the same genetic information) whilst mosses (and other
   bryophytes) have only a single set of chromosomes ( haploid, i.e. each
   chromosome exists in a unique copy within the cell). There are periods
   in the moss lifecycle when they do have a full, paired set of
   chromosomes but this is only during the sporophyte stage.
   Life cycle of a typical moss (Polytrichum commune)
   Enlarge
   Life cycle of a typical moss (Polytrichum commune)

   The life of a moss starts from a haploid spore, which germinates to
   produce a protonema, which is either a mass of filaments or thalloid
   (flat and thallus-like). This is a transitory stage in the life of a
   moss. From the protonema grows the gametophore ("gamete-bearer") that
   is differentiated into stems and leaves ('microphylls'). From the tips
   of stems or branches develop the sex organs of the mosses. The female
   organs are known as archegonia (sing. archegonium) and are protected by
   a group of modified leaves known as the perichaetum (plural,
   perichaeta). The archegonia have necks called venters which the male
   sperm swim down. The male organs are known as antheridia (singular
   antheridium) and are enclosed by modified leaves called the perigonium
   (plural, perigonia).

   Mosses can be either dioicous (compare with dioecious in seed plants)
   or monoicous (compare monoecious). In dioicous mosses, both male and
   female sex organs are borne on different gametophyte plants. In
   monoicous (also called autoicous) mosses, they are borne on the same
   plant. In the presence of water, sperm from the antheridia swim to the
   archegonia and fertilisation occurs, leading to the production of a
   diploid sporophyte. The sperm of mosses is biflagellate, i.e. they have
   two flagella that aid in propulsion. Without water, fertilisation
   cannot occur. After fertilisation, the immature sporophyte pushes its
   way out of the archegonial venter. It takes about a quarter to half a
   year for the sporophyte to mature. The sporophyte body comprises a long
   stalk, called a seta, and a capsule capped by a cap called the
   operculum. The capsule and operculum are in turn sheathed by a haploid
   calyptra which is the remains of the archegonial venter. The calyptra
   usually falls off when the capsule is mature. Within the capsule,
   spore-producing cells undergo meiosis to form haploid spores, upon
   which the cycle can start again. The mouth of the capsule is usually
   ringed by a set of teeth called peristome. This may be absent in some
   mosses.

   In some mosses, 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 fertilisation. This is a means of
   asexual reproduction.

Classification of mosses

   Two different types of mosses (and a lichen, in the smallest box)
   surround this tree trunk.
   Enlarge
   Two different types of mosses (and a lichen, in the smallest box)
   surround this tree trunk.
   Ant on mosshill
   Enlarge
   Ant on mosshill

   Mosses were traditionally grouped with the liverworts and hornworts in
   the Division Bryophyta ( bryophytes), within which the mosses made up
   the class Musci. This group, however, is paraphyletic and now tends to
   be split up. In such system, the Division Bryophyta refers specifically
   to mosses. They appear to be the closest living relatives of the
   vascular plants.

   The mosses are grouped as a single class, now named Bryopsida, and
   divided into seven subclasses:
     * Andreaeidae
     * Sphagnidae
     * Tetraphidae
     * Polytrichidae
     * Buxbaumiidae
     * Bryidae
     * Archidiidae

   Andreaeidae 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.

   The Sphagnidae, the peat-mosses, comprise the single genus Sphagnum.
   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.

   The Tetraphidae are unique (as their name implies) in having only four
   large peristome teeth surrounding the opening of the capsule.

   Polytrichidae have leaves with lamellae, which are flaps on the leaves
   that look like the fins on a heat sink. These help it retain moisture.
   They 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 high.

   The Buxbaumiidae are called 'bug mosses' because they usually have a
   very small and reduced gametophore and the whole plant is mostly the
   sporophyte capsule. The shape reminds one of a bug, which is the reason
   for its common name.

   The Bryidae are the most diverse group; over 95% of moss species belong
   to this subclass.

   The Archidiidae are distinguished by their extremely large spores and
   the way the sporangium develops.

Habitat

   Moss growing in the shelter of the growth rings of a stump
   Enlarge
   Moss growing in the shelter of the growth rings of a stump
   Moss on a rock
   Enlarge
   Moss on a rock
   Young sporophyte of the common hair cap moss (Polytrichum commune)
   Enlarge
   Young sporophyte of the common hair cap moss (Polytrichum commune)

   Mosses are found chiefly in areas of low light and dampness; any area
   of the world. Mosses are common in wooded areas and at the edges of
   streams. Mosses are also found in cracks between paving stones in damp
   city streets. Some types have adapted to urban conditions and are found
   only in cities. A few species are wholly aquatic, such as Fontinalis
   antipyretica, and others such as Sphagnum inhabit bogs, marshes and
   very slow-moving waterways. Such aquatic or semi-aquatic mosses can
   greatly exceed the normal range of lengths seen in terestial mosses.
   Individual plants 20-30 cm or more long are common in Sphagnum species
   for example.

   Wherever they occur, mosses require moisture to survive because of the
   small size and thinness of tissues, lack of cuticle (waxy covering to
   prevent water loss), and the need for liquid water to complete
   fertilisation. Some mosses can survive desiccation, returning to life
   within a few hours of rehydration.

   In northern latitudes, the north side of trees and rocks will generally
   have more moss on average than other sides. This is assumed to be
   because of the lack of sufficient water for reproduction on the
   sun-facing side of trees. South of the equator the reverse is true. In
   deep forests where sunlight does not penetrate, mosses grow equally
   well on all sides of the tree trunk.

Cultivation

   Moss is 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. Rules of cultivation are not widely established. Moss
   collections are quite often begun using samples transplanted from the
   wild in a water-retaining bag. However, specific species of moss can be
   extremely difficult to maintain away from their natural sites with
   their unique combinations of light, humidity, 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.

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.

Commercial use

   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. There are growing concerns in parts of the world where
   this trade is growing, that significant environmental damage may be
   caused by commercial peat harvesting. In World War II, Sphagnum mosses
   were used as first-aid dressings on soldiers' wounds, as these mosses
   are highly absorbant and have mild antibacterial properties. Some early
   people used it as a diaper due to its high absorbency.

   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 Finland peat mosses have been used to make bread during famines.

   Retrieved from " http://en.wikipedia.org/wiki/Moss"
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   with only minor checks and changes (see www.wikipedia.org for details
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