Leafy mosses

Stalk

The stem ( caulidium ) of leafy mosses is always there, covered with leaves. The reproductive organs are located on top ( acrocarpous or green mosses) or on the sides ( pleurocarpous or amniotic mosses) of the stem. Acrocarpous mosses have an upright stalk ( orthotropic mosses), pleurocarpous mosses have a horizontal stem ( plagiotropic mosses) lying, hanging or floating. In fact, in plagiotropic mosses, the reproductive organs sit on the tops of shortened side shoots , so that the division into acrocarp and pleurocarpous mosses is formal and allows for many transitional forms.

In the transverse section, the stem is rounded, sometimes oval, angular or ribbed. It may be of homogeneous cells , but in most mosses it consists of differentiated ones. In the latter case, a bark or scleroderma is formed, from a mechanical tissue , inside of which there is a main, conductive tissue . Dead cells of the inner cortex form the outside of the epidermis , one or more layers of dead cells without living contents, which serve to preserve water.

Mechanical tissue is formed by stereids - elongated, narrow, prosenchymal cells. Usually they have a yellowish, brown, red-brown, purple or almost black color. The walls of the stereids are thick, sometimes until the lumen is almost completely gone. In the inner parts of the walls there are water-conducting pores. The inner surface of the wall can form papilliform outgrowths, which grow in a dense network into the cell cavity. They serve to store water , so cells can swell. The main function of the inner cortex is to ensure the strength of the stem.

In some mosses, the outer layer of the cortex is formed by hyaloderm cells - without chloroplasts , with thin, transparent walls and a wide lumen.

Stomata in the epidermis of the stem are absent in all leafy mosses. This is due to the fact that they, in fact, are not needed by mosses, with their absence of real integumentary tissue, which requires adjustment of absorption and excretion processes. Both water absorption and its evaporation are carried out immediately by the entire surface of the gametophyte.

The deeper, the less thick the walls of the cells of the cortex, which gradually passes into the underlying tissue . Less commonly, the cortex is sharply delimited from the main tissue ( Meesia longiseta ). The main tissue consists of homogeneous parenchymal cells abundantly filled with cytoplasm , chloroplasts, starch , and fatty oils . In a cross section, cells are often collenchymally (in the form of triangular swellings at the corners) thickened. The main tissue provides photosynthesis , is used to preserve water, starch and oil reserves, as well as secretion products ( calcium oxalate ). The main function of the main tissue is water-conducting.

Sometimes in the main tissue there may be groups of small thin-walled cells, continuing in the stem of the leaf vein, leaf traces. Some end in the main tissue of the stem and do not reach the central bundle (the so-called false leaf traces), others are connected to the central bundle ( real leaf traces). Real leaf traces can be differentiated into fabrics ( splachnum ).

The central bundle , or the conducting bundle, passes along the axis of the stem, consists of elongated, oblique transverse septa, mostly thin-walled cells with a narrow clearance. Sometimes the cells of the central bundle are thick-walled and stained ( Dicranum scoparium , Hypnum species). Usually the conductive bundle is clearly delimited from the main tissue. The central beam provides water conduction and its conservation. Not available in all species and genera. In the absence of a central bundle, its function is performed by the main tissue filling the entire stem.

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  Cross section of the stem Rhizomnium punctatum

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  He is in a larger magnification

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  Orthotrichum lyellii

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  Hedwigia ciliata

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  Catoscopium nigritum

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  Anomobryum concinnatum

Hairy formations - rhizoids can form from any surface cell of the stem. These are single-row multicellular filaments with brown, purple or reddish longitudinal shells and with oblique transverse partitions. Using rhizoids, mosses are attached to the substrate and adsorb water from the environment. In addition, rhizoids are capable of photosynthesis. They are formed over the entire surface of the stem, but most often - at the base of the upright stem or on the abdominal side of the creeping or lying stem facing the substrate. Sometimes rhizoids cover the entire stem with thick felt, light or colored in brown, purple or reddish color. In some mosses, rhizoids curl into long strands.

Rhizoid felt raises water from the soil and for a long time stores it in the capillary spaces between the rhizoids and the plant. Rhizoids of water mosses attach them to the substrate, the adsorption function for them is not so relevant. For more reliable fastening at the ends of the rhizoids of water mosses, forked branches are formed, sometimes woven into pads. With changes in nutrition and lighting, rhizoids can turn into a green secondary protonema .

At the apex of the stem, in the axils of the leaves, at the place where the leaves leave the stem during growth, threadlike formations from several cells arise - club-shaped hairs. Their terminal cell secretes mucus that protects the growth points of the stem from drying out.

Some amyloid mosses on the stem develop outgrowths of the stem - paraphillia ( Greek para - near, Greek phyllon - leaf). They are green, filiform or leaf-shaped, simple or branched. Sometimes paraphillia grows so dense that they wrap the stem in thick green felt. The forms of paraphyllia take a variety of forms; they are located on the stem without any order. Veins never have. They can not only conduct and retain water, but also perform the function of photosynthesis. Filamentous paraphillia are attached to the stem of one, and leaf-shaped - with two or more base cells.

The stem never branches in two. Always lateral shoots are formed on the main, below the leaf, never - in the sinuses.

Branching of mosses is of two main types: sympodial and monopodial.

Acrocarpous mosses branch mainly in the sympoidal type. Branching is weak, usually only in the upper part. Innovations , that is, new lateral branches, form under the reproductive organs and grow in the direction of the main stem, at the top they can again give gametangia.

Branching can be sympoidal type (shoots occur one at a time), forked type (paired shoots) or bunch-like type (several shoots at once). The forked and bundle-like branching here is a special case of the sympoidal, where two or more innovations arise at once. After the death of the main stem, innovations, taking root, become independent plants.

In amygdala mosses, the stems branch monopodially. There is a pronounced main shoot, from which side branches depart. On each side of the stem, the branches appear in an ascending ( acropetal ) sequence. The younger the shoot, the closer it is to the top. New branches grow weakly, since the main shoot does not die off for a long time and continues to grow.

With the correct alternation of the rudiments of the branches, the branching of the stem is pinnate; with repeated branching (the formation on the lateral shoots of branches of the second and third order) - twice or thrice-branching.

The growth of shoots and the development of branches in both the green and amygdala mosses depends on the growth point of the main stem. If you remove the top of the stem, then resting buds will develop into shoots.

Leaves

Leaves ( phyllids or phyloids ) are always sessile, leafless, usually transversely attached to the stem, always arranged in a spiral, in three or five rows, occasionally in two rows. Never settle opposite or whorled. Laid in ascending order. Leaves are formed by dividing the bilateral apical cell, from which segments are separated on both sides. Segments are divided by partitions always only in one plane. With the cessation of apical growth of the leaf, its final size is achieved by insert growth at its base.

By location on the stem are divided into lower, middle and integumentary.

Stem leaves are median, located in the middle and upper parts of the stem. The branch leaves of most mosses do not differ from the stem shape, only in smaller sizes. But in some mosses, the leaves on the branches can take a different shape than on the main shoot. They are located very close to each other, covering the entire leafy surface of the stem.

The integumentary leaves surround the reproductive organs, usually much larger than the stem ones, differ from them in shape, and often in structure, sometimes color. The integumentary leaves surrounding the archegonia are called perichecial , and the integumentary leaves surrounding the anteridia are called perigonial .

The grassroots leaves are strongly reduced, much smaller than the stem, scaly. They develop in the lower aerial or underground part of the stem in mosses with rhizomes. Often do not have chlorophyll.

The leaves of mosses are simple, solid, on the edge can be serrated and extremely rarely deeply separated. The leaf blade is most often single-layer, less often it is wholly or partially bilayer or multilayer. The plate may be flat, cupped, spoon-shaped, grooved, folded, keeled, grooved or wavy. The surface can be smooth and shiny, or velvety and dull. Leaf cells are rich in chloroplasts and perform the function of photosynthesis . The vein, if it is developed at all, extends in the middle of the leaf and consists of thick-walled, elongated cells. In addition to the mechanical retention of the sheet, the vein provides the conductivity of plastic substances and water. Peels, stomata on a sheet never happen.

In the plate of the leaf, the base, apex, edge, border, wings and ears are distinguished.

The base is the place where the leaf is attached to the stem. The opposite end is called the tip. Leaf wings or leaf ears develop at the corners of the base of the leaf. Ears differ sharply in shape, color and size from other cells and serve to preserve water. The border of the sheet is formed by long and narrow cells located in one or more rows along the edge of the sheet.

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  The base of Bryum alpinum

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  The top of Bryum capillare

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  Edge of Mnium spinosum

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  Scleropodium purum wings

The shape of the leaves is very diverse - from round to awl-shaped. The most common forms are:

• rounded
• ovoid;
• elliptical;
• linguistic;
• lanceolate;
• subulate.

The structure of the edges of the leaves is diverse. Turning away, bending or unbending, the edge of the sheet creates microscopic cavities where capillary water is held. The wrapped edge of the leaf is characteristic of moss that lives in conditions of periodic drought , since it performs a protective function, protecting the leaf from drying out.

Leaf cells are of two main types: parenchymal - usually rounded or polygonal (often square and hexagonal), of almost the same length and width, and prosenchymal - narrow, elongated, straight, curved, worm-shaped with pointed, protruding ends. Leaf plate cells are rarely the same. The upper part of the leaf usually consists of thick-walled parenchymal small cells, sometimes mamillous (conical outgrowths of cells without thickening of the cell walls) or papillose. The base cells are always somewhat larger and differ sharply from the upper cells in shape.

Papillomas (thickening of the cell wall) are most characteristic of breeze mosses . They greatly increase the suction surface of the cell, contribute to a more rapid intake of water and its passage into the cell. Papillas especially often develop on the cells of mosses that grow in dry and highly illuminated places, but are also widespread among those growing in conditions of excessive humidity.

A number of systematically distant groups of mosses show a clear separation of the assimilation and aquifer elements of the leaf.

In green mosses, the leaf vein is usually simple, unbranched. Bowl mosses can have completely different veins or even not have them at all from representatives of the same family. The vein can be simple - in one lane; double, diverging immediately from the base of the sheet into two rays; fork - a simple vein with short branches.

In most cases, the vein passes only along the lower side of the leaf, and only some mosses have it on the upper side. A variety of structural formations often grow on the underside of the vein. In the family of Pottiidae in the genera Aloina ( Aloina Kindb. ) And Crossidium ( Crossidium Jur. ), Multicellular, sometimes branched filaments rich in chloroplasts, which are often woven into a pillow, sprout in the upper part of the leaf from the vein.

The assimilation plates and strings on the leaves of mosses probably perform the same functions: in some mosses, assimilation, in others - ensuring the absorption of water. When most of these mosses dry, the edges of the leaves are wrapped, covering the plates and threads tightly on top. Breakable leaf strands are capable of vegetative propagation.

In most arthropod mosses, the vein has a complex structure. It consists of pointers, escorts, stereoid bundles and external cells. Parenchymal cells of the leaf vein with a wide lumen, thin-walled, poor in plasma contents, located in one, less often in two rows, are called pointers . They conduct water and often have pores on the longitudinal walls. In wet weather, signs are filled with water. As a result, the vein swells and stretches, and with it the plate of the sheet is stretched. In dry weather, the vein dries up, loses tension, bends inward, and with it the leaf plate bends as well. Accompanyers are thin-walled, elongated cells of small diameter, combined into a cord and resembling cells of the central bundle of the stem. They are almost always on the top of the signs. Accompanyers are rich in plasma. Pointers and escorts are called characteristic vein cells. They are usually on the dorsal side or on both sides, less often only on the abdominal side, stereids are adjacent.

External cells (usually with a fairly wide lumen) form the epidermis of the vein. They usually lie only on one side of the vein - either dorsal or abdominal. Their function is protective. Vein stereids are thick-walled, elongated in length and connected in a cage strand. They are similar to the bast fibers of vascular plants and do not differ in structure from stereoid stem cells. The mechanical tissue of the vein forms a single ribbon-like stereoid bundle in the middle of the vein, in a number of species - two, dorsal and abdominal, separated by pointers. Stereids strengthen the vein.

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  Anomobryum concinnatum leaf

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  Catoscopium nigritum leaf

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  Cinclidium stygium leaf

Reproductive organs

The reproductive organs of mosses are most often grouped. They are usually surrounded by integumentary leaves. In acrocarpous mosses, gametangia are formed on the tops of the main shoots. Pleurocarpous on very short lateral branches. Between anteridia (male genital organs) and archegonia (female genital organs) there are often filiform or club-shaped paraphyses . Paraphyses of anteridial shoots are able to absorb and retain moisture. The paraphyses around the archegonium cover it, protecting it from adverse conditions.

Some species of moss are monoecious, others are dioecious. The dichotomy in mosses is apparently relative, since both female and male specimens can form on the same protonemus. Under conditions of malnutrition, male gametophytes form on the protonemia, and with good nutrition, female gametophytes.

Leafy mosses have pronounced sexual dimorphism . Female plants that need to nourish young sporophytes are usually larger and more developed. Male plants in dioecious species are often strongly reduced. Sometimes male plants are simply dwarfs, dying after the formation of anteridia.

In some species of hypnum, spores germinate directly on the leaves of female plants and dwarf male plants grow out of them.

In some species of mosses, generative and vegetative shoots differentiate. Other species do not have such differentiation.

Mature anteridia are ellipsoidal, club-shaped, rarely spherical (in the buxbaumium genus) bodies, often on a short multicellular stalk. Under a single-layer wall of anteridium is spermatogenic tissue, from which flagellate spermatozoa form. Inside the perigonium, usually not simultaneously, a large number of anteridia are formed. Mature anteridia open when it rains or dew. Sperm cells move towards archegonium through water.

Archegonium usually has the shape of a bottle-shaped body on a massive leg. The upper narrow part of the archegonium is called the neck, the lower expanded part is called the abdomen. Inside the neck there are cervical tubular cells, in the abdomen - one or two abdominal tubular cells. At the bottom of the abdomen is one large egg. The abdominal cell and tubule cells of the neck of a mature archegon are covered with mucus . The integumentary cells of the neck, as in anteridia, secrete mucus and burst, forming a passage leading to the ovum . Sperm cells due to chemotaxis move to this mucus and fertilize the egg.

Although several archegonies develop in perichetia, in most species only one of them is fertilized. Accordingly, only one sporogon grows. However, in some species in the same perichecia several archegonia are fertilized at once, of which several sporogons grow.

As a result of fertilization of the egg in the abdomen of archegonium, a zygote is formed. The lower cell in the process of division forms the lower part of the leg and foot, which grows through the wall of the abdomen of the archegonium to the gametophyte tissue. A box is formed from the upper (apical) cell of the divided zygote.

As the young sporophyte grows, a stalk-like body develops, which then differentiates into a box and a foot with a foot . An elongating sporophyte ruptures across the overgrown archegony surrounding it. The box lifts the upper part of the torn archegonium in the form of a cap , and the lower part ( vagina ) of the archegonium surrounds the base of the leg with a collar.

Cap - a film formation that covers the young box from above, in whole or in part, protecting it from external influences. The cap is usually tight, for the most part layered. The narrowed brownish top of the cap often corresponds to the neck of the archegon. The wrapper of the embryo, called the epigone , is initially integral, is formed due to the archegony, its legs, and, partly, the stem .

In most leafy mosses, the cap is well developed, apart from some cleistocarp ephemers from brie . The shape of the caps can be very diverse. The cap usually falls even before the box is fully developed, less often it stays on the box for a long time and falls with the cap.

In most of the shaving legs, it is well developed, but its length varies widely even among representatives of the same family. In some genera, the brie leg is completely absent or present, but does not reach full development. Usually this is the case with ephemera with capsules closed by an inseparable lid and immersed in perichecial leaves. In many types of tissue, the sporogony legs are the same as in the gametophyte stem. Outside the legs are thick-walled cells of mechanical tissue, then the parenchyma of the cortex, in the center there is a cord of conducting prosenchymal cells.

The stem of most leafy mosses is very sensitive to fluctuations in air humidity. Drying, the leg spirally spirals and pushes the box, actively dispersing the spores. External stereoid cells are also located in a spiral. The reason for the hygroscopic movement of the leg is the ability of the outer walls of the stereids to quickly absorb moisture, swell and unwind the leg, and when dried, on the contrary, quickly lose water and twist the leg.

The foot, that is, the lower part of the leg, goes deep into the gametophyte tissue and attaches sporogonum to it. The main function of the foot is to obtain from the gametophyte the substances necessary for the development of the fetus. In some mosses, the foot consists of homogeneous cells, in others, surface cells extend into the papillae like root hairs. Sometimes they even generate branched multicellular rhizoids . These rhizoids actively absorb water and nutrients. The central bundle of the leg can continue further into the foot, and often even penetrates the central bundle of the stem.

Влагальце передаёт питательные вещества от гаметофита к растущему спорофиту через стопу. Гаметофит и спорофит не образуют прочной связи, спорофит легко отделяется от гаметофита.

Коробочка состоит из крышечки , колечка , урны , шейки и апофизы , если последняя вообще есть. У некоторых видов коробочки имеют неотделяющуюся крышечку. Такие мхи называются клейстокарпными ( закрытоплодными ). Мхи с отделяющейся крышечкой называются стегокарпными ( крышкоплодными ). Крышечка прикрывает собой устье коробочки и отпадает после созревания спор . В сбрасывании крышечки участвуют колечко и зубцы перистома. Ко времени созревания коробочки ткани колечка значительно натягиваются, помогая сбросить крышечку.

Колечко располагается между верхним краем урны и крышечкой. Оно состоит из лежащих друг над другом в один или несколько рядов уплощённых бесцветных, сильно гигроскопичных клеток. При набухании этих клеток колечко расширяется и отделяется и от урны, и от крышечки. Колечко представляет собой полоску в виде пояса, клетки его крупные.

Урной называют часть коробочки, внутри которой развиваются споры. В верхней части урны находится широкое или суженное отверстие — устье , закрытое крышечкой. По краю устья часто формируются выросты в виде зубцов разнообразной формы, которые называются перистомом или околоустьем .

Стенки коробочки состоят из двух или нескольких слоев. Наружный слой — экзотеций , гомологичный эпидерме высших растений, кутинизирован . Клетки экзотеция бедны плазмой, их наружные оболочки обычно утолщены и плотно прилегают друг к другу. Внутренние слои стенки коробочки состоят из крупных паренхиматических клеток с тонкими бесцветными клеточными оболочками, они образуют водоносную ткань.

The cells of the walls of the young sporogon are rich in chloroplasts ; as they mature, the number of chloroplasts decreases. Exotice ceases to fulfill its assimilation function, leaving only the mechanical one. In the exotice of the lower half of the urn and neck are stomata. Superficial stomata are located at the level of exotice, submerged stomata are located below its level. The stomata is of the usual form of two symmetrical kidney-shaped closure cells with a gap. Bride from the genera archidium , schistosteg , tetrafis stomata are completely absent.

Under exotecia lies a single-layer, two-layer or four-layer aquiferous tissue. The cells of the aquifer are larger than the cells of exotice, they are thin-walled and filled with water. The aquifer supplies water to an even deeper assimilation tissue . Due to the thin walls and transparency of the cells, the aquifer transmits light rays to the chloroplasts .

In most mosses, between the walls of the capsule and the spore sac there is an air cavity penetrated by threads from chlorophyll-bearing cells. The air cavity and assimilation tissue are absent in childbirth, where the spore bag directly adjoins the wall of the capsule, as well as in water mosses.

In the center of the urn is a column . It consists of prosenchymal cells that conduct water and nutrients to developing spores. The column usually passes in a box from the neck to the cap. In few species, it extends, protrudes out of the urn and raises the remaining lid attached to it. After the cap falls off, in many mosses, the column shrinks and remains at the bottom of the urn.

The cirrus consists of teeth located one or two rows, of cilia or threads of various shapes. In some mosses, there is no pinnate, while in others it is underdeveloped, rudimentary .

The teeth of a single-row peristome and exostome (outer row) of the double peristome are capable of hygroscopic movement. They consist of two plates having a different anatomical structure, and, accordingly, a different degree of hygroscopicity. The movement of the teeth actively helps to sow spores from the urn and distribute them as widely as possible. Also, with these movements, the teeth close the mouth of the urn with high humidity , preventing spores from getting wet and germinating inside the box.

The lower part of the box, not containing a spore, the neck , gradually or suddenly passes into the leg. Often the tissue on the neck unilaterally grows, forming a goiter . Goiters are characteristic of some mosses from dikranovye .

Apophysis is a swelling of the lower part of the capsule, which takes a variety of forms. The bright color of the pituitary gland and the liquid with an unpleasant odor secreted by it through the stomata attract flies that become spores.

Disputes

Spores of leafy mosses are usually unicellular formations containing chloroplasts and oil droplets. Their sizes vary greatly, but most often have a diameter of 10-12 microns. In some genera, mainly tropical, spores are multicellular, starting to germinate, while still in sporangia.

Usually, spores of leafy mosses are spherical, rarely oval, sometimes weakly rounded-angular, rarely kidney-shaped.

Spores of mosses are very viable, can tolerate both drought and cold. Dry spores after freezing them at a temperature below - 200 ° C for several hours normally sprouted on nutrient media. They tolerate short-term heating up to +100 ° C.

Under optimal conditions of illumination, temperature, humidity and the reaction characteristic of this type of substrate reaction, spores usually grow in a few days or weeks. From germinating spores, a primary protonema develops on which the kidneys are laid. Young plants grow from the buds.

With the swelling of the spores, the exin (outer strong shell) bursts, and the intin is extended in the form of a papilla along with the contents of the spore. By dividing, it gives rise to either a single-row thread or a single-layer (rarely multilayer) plate carrying rhizoids. This stage of gametophyte development is called a protonema. The first gametophyte cell is covered only by intina (a thin film of cellulose and pectin) and is defenseless against the influence of the external environment. Under the slightest adverse conditions, it is doomed to death. The protonema consists of a green chloronema (photosynthetic) and the underground part - a colorless rhizema. The magnitude, form, and life span of protonema in leafy mosses vary significantly. The branching protonema of some species of moss covers an area of ​​up to 1 m ² and lasts for months. In species with annual small gametophytes, the protonema can live for several years. Usually, the protonema’s dimensions reach several centimeters, and the life expectancy is several days or weeks.

Vegetative propagation

A secondary protonema in the form of a thread on which buds are formed, and then young plants, or special devices for vegetative propagation (brood bodies, leaves, buds, etc.) can form almost any part of the gametophyte of leafy mosses.

As the moss sod grows, young shoots separate from it at the moment when the lower part of the mother plant dies. This is the most common method of vegetative propagation of mosses.

It can be propagated by parts of the body - fragments of stems, buds and branches, brood branches, brood buds (shortened brood branches with unreduced or reduced leaves), leaf fragments, brood leaves.

Brood leaves separate entirely and usually differ from other leaves. Sometimes brood leaves are collected in heads at the end of the peduncle.

Brood filaments , like kidneys, usually form in the sinuses. They are filiform formations, sometimes branched, often colored, smooth or papillous.

In addition, brood bodies — multicellular formations for vegetative propagation — can occur on any part of the plant. They are formed on the secondary protonema, on the stem rhizoid felt, on the stem in the axils of the leaves, on various parts of the leaf vein, on the cells of the leaf blade. By the time the brood body is separated, at its junction with the mother plant, a dividing cell forms with a very delicate outer wall, which is easily destroyed. In the most frequent places of formation, stem, leaf and axillary brood bodies are distinguished. Brood bodies can have different shapes and colors, be single or crowded.

Brood organs are spread by air currents, water, carried by animals.

In the past, all mosses were included in the Bryopsida group. The current composition of the group is more limited.

In the classification proposed by Goffinet B. and WR Buck in 2006, the class includes 6 subclasses ^{[1] [2]} :

• subclass Buxbaumiidae (the only genus Buxbaumia ( Buxbaumia ))
• subclass Diphysciidae (the only genus Diphyscium ( Diphyscium ))
• subclass Timmiidae (only genus Timmia )
• subclass Funariidae (5 families)
• subclass Dicranidae (24 families)
• subclass Bryidae (71 families)

More detailed phylogeny to the level of orders of work of Novikov and Barabash-Krasny 2015. ^[3]

• Plant life. Volume 4. Mosses. Plankton. Horsetail. Ferns. Gymnosperms // Ed. I.V. Grushivitsky, S.G. Zhilin. - M .: Education, 1978.- 447 p.
• Sluka Z.A. Green Mosses. - M.: Publishing house of Moscow University, 1980. - 134 p.