BRYOPHYTA

          Characterstics

• Mosses are non-vascular plants in the land plant division Bryophyta

• Differ from vascular plants in lacking water-bearing  xylem tracheids or vessels. As                          in liverworts   and  hornworts, the haploid gametophyte generation is the dominant phase of the life cycle.

• The diploid sporophyte generation is dominant. Mosses reproduce using spores, not  seeds and have no flowers.

• Most of plants have two sets of chromosomes in  vegetative cells , called Diploid.  Each chromosome has a partner that contains the same, or similar, genetic information.  Mostly mosses and other bryophytes have only a single set of chromosomes called haploid.

                       Life cycle

• The moss life-cycle starts with a haploid spore that germinates to produce a protonema (pl. protonemata), ( a mass of thread-like filaments or thalloid) (flat and thallus-like).

• Protonema grows in damp soil, tree bark, rocks, concrete, or  any other stable surface. This is a transitory stage in the life of a moss,

• But from the protonema grows the gametophores ("gamete-bearer") that is structurally differentiated into stems and leaves

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• A single mat of protonemata may develop several gametophores shoots, so called a clump of moss.

• Tip of the gametophore stems or branches develop the sex organs.. 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 are small flask-shaped clumps of cells with an open neck (venter) down which the male sperm swim. The male organs are known as antheridia(sing. antheridium) and are enclosed by modified leaves called the perigonium (pl. perigonia). The surrounding leaves in some mosses form a splash cup, allowing the sperm contained in the cup to be splashed to neighboring stalks by falling water droplets.

• Mosses can be either dioicous (compare dioecious in seed plants) or monoicous (compare monoecious).

• In dioicous mosses, male and female sex organs are borne on different gametophyte plants.

• In monoicous (also called autoicous) mosses, both are borne on the same plant. In the presence of water, sperm from the antheridia swim to the archegonia and fertilization occurs, leading to the production of a diploid sporophyte.

• The sperm of mosses is biflagellate, i.e. they have two flagellate that aid in propulsion. Since the sperm must swim to the archegonium, fertilization cannot occur without water. After fertilization, 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.

• Most mosses rely on the wind to disperse the spores.

• In 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.

• Recently it found that microarthropods, such as springtails and mites, can affect moss fertilization and this process is mediated by moss-emitted scents. Male and female fire moss, e.g. emit different and complex volatile organic scents. Female plants emit more compounds than male plants.

•  Springtails it found that Springtails prefer to choose female plants, and one study found that springtails enhance moss fertilization, suggesting a scent-mediated relationship analogous to the plant-pollinator relationship found in many seed plants.

• The stink moss species Splachnum sphaericum develops insect pollination further by attracting flies to its sporangia with a strong smell of carrion, and providing a strong visual cue in the form of red-coloured swollen collars beneath each spore capsule.

• 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.