Where is the gametophyte in moss

Liverwort plants can also reproduce asexually by the breaking of branches or the spreading of leaf fragments called gemmae. In this latter type of reproduction, the gemmae small, intact, complete pieces of plant that are produced in a cup on the surface of the thallus are splashed out of the cup by raindrops.

The gemmae then land nearby and develop into gametophytes. The hornworts Anthocerotophyta belong to the broad bryophyte group that have colonized a variety of habitats on land, although they are never far from a source of moisture. The short, blue-green gametophyte is the dominant phase of the lifecycle of a hornwort. The narrow, pipe-like sporophyte is the defining characteristic of the group. The sporophytes emerge from the parent gametophyte and continue to grow throughout the life of the plant.

Stomata appear in the hornworts and are abundant on the sporophyte. Photosynthetic cells in the thallus contain a single chloroplast. Meristem cells at the base of the plant keep dividing and adding to its height. Many hornworts establish symbiotic relationships with cyanobacteria that fix nitrogen from the environment.

Hornworts : Unlike liverworts, hornworts grow a tall and slender sporophyte. The life cycle of hornworts also follows the general pattern of alternation of generations and has a similar life cycle to liverworts. The gametophytes grow as flat thalli on the soil with embedded gametangia. Flagellated sperm swim to the archegonia and fertilize eggs. However, unlike liverworts, the zygote develops into a long and slender sporophyte that eventually splits open, releasing spores.

Additionally, thin cells called pseudoelaters surround the spores and help propel them further in the environment. Unlike the elaters observed in liverworts, the hornwort pseudoelaters are single-celled structures. The haploid spores germinate and produce the next generation of gametophytes. Like liverworts, some hornworts may also produce asexually through fragmentation.

Life Cycle of Hornworts : The life cycle of hornworts is similar to that of liverworts. Both follow the pattern of alternation of generations. However, liverworts develop a small sporophyte, whereas hornworts develop a long, slender sporophyte.

Liverworts also disperse their spores with the help of elaters, while hornworts utilize pseudoelaters to aid in spore dispersal. Mosses are bryophytes that live in many environments and are characterized by their short flat leaves, root-like rhizoids, and peristomes.

More than 10, species of mosses have been cataloged. Their habitats vary from the tundra, where they are the main vegetation, to the understory of tropical forests.

Mosses slow down erosion, store moisture and soil nutrients, and provide shelter for small animals as well as food for larger herbivores, such as the musk ox. Mosses are very sensitive to air pollution and are used to monitor air quality. They are also sensitive to copper salts. Such salts are a common ingredient of compounds marketed to eliminate mosses from lawns.

Mosses form diminutive gametophytes, which are the dominant phase of the life cycle. Green, flat structures resembling true leaves, but lacking vascular tissue are attached in a spiral to a central stalk or seta. In the majority of stegocarpous mosses, spore dispersal is mediated by the peristome, a circular system of teeth that is inserted on the mouth of the urn, to the inside of the operculum.

The developmental history and architecture of the peristome provide a suite of important systematic characters Fig. Peristomes are of two fundamentally different types, nematodontous, which are found only in Polytrichopsida and Tetraphidopsida, and arthrodontous.

In a nematodontous peristome, the teeth are constructed of bundles of whole, dead cells. Commonly in the Polytrichopsida, 32 or 64 rarely 16 short lingulate teeth, comprised of up to four layers of vertically elongate, very thick-walled cells, are attached by their inner surface to a membranous expansion of the columella called the epiphragm. The release of the operculum exposes small slits between the teeth through which the spores are slowly released.

In the Tetraphidopsida, there are four erect, wedge-shaped peristome teeth, each of which represents a quadrant of the peristomial cell layers. In contrast to the cellular peristomes of these taxa, arthrodontous peristomes, found in the rest of stegocarpous mosses, consist at maturity only of remnants of paired, periclinal cell walls.

As reviewed by several authors e. Edwards ; A. Shaw and H. Robinson ; W. Buck and B. Goffinet , arthrodontous peristomes differentiate from the three innermost layers of the amphithecium formed by fundamental square divisions K. Goebel —, vol. Following H. Blomquist and L. The number and arrangement of cells in the peristomial layers cannot always be determined with certainty in mature capsules, so peristomial formulae are generally not included in taxonomic descriptions.

Arthrodontous peristomes are of two major types, namely, haplolepidous and diplolepidous Fig. The haplolepidous peristome consists of a single ring of 16 teeth that are formed by cell wall deposition on the paired walls of the PPL and IPL. The peristomial formula is always 0 4 , with a single column of PPL cells forming the outer dorsal surface of each tooth, and unequal parts of two IPL cells forming the inner ventral surface. The teeth can be forked at their apices, as in the Dicranaceae, or be fused at the base into an elongate tube, or basal membrane, or be divided into 32 long narrow, filaments, e.

Development from the OPL is highly reduced or absent, forming at best prostomial bumps at the base of the peristome S. Edwards Diplolepidous peristomes have the same number of cells in the OPL and PPL as haplolepidous peristomes, but display substantial variation in the IPL numbers, with peristomial formulae ranging from to The exostome typically consists of 16 teeth, equal to the number of cells in the PPL, while the outer surface of each tooth bears a divisural line that marks the two columns of cells of the OPL.

The teeth may be joined together in pairs, or secondarily divided, and are often highly ornamented, especially on the outer surface A. Shaw The architecture of the endostome is likewise variable, with different patterns of surface ornamentation on outer and inner surfaces Shaw and J. Rohrer In a diplolepidous-alternate peristome D. Vitt of the bryoid or hypnoid type, the endostome comprises a basal, often keeled membrane, topped by 16 broad, perforate segments that alternate with the exostome teeth.

One to four uniseriate cilia occur between the segments, opposite the exostome teeth. In some taxa, the endostome segments are highly reduced or absent, and the inner peristome consists only of cilia Fig. In contrast, in the diplolepidous-opposite peristome of the Funariales, there is no basal membrane, the endostome segments occur opposite the exostome teeth, and there are no cilia Fig.

Movements of the exostome teeth of diplolepidous taxa as well as the single ring of teeth of haplolepidous taxa are due to the differential composition of the wall deposits on the outer versus the inner surfaces of the teeth. Specifically, one surface readily absorbs water and elongates, while the other does not. This differential response to water absorption causes the teeth to bend when moistened.

In many taxa the teeth close over the mouth of the capsule when moistened, so spores are released only when the air is dry, but in others they bend outward when wet, allowing spore release in moist conditions D. Mueller and A. Neumann With drying, the teeth return to their original stance. This process can be repeated several times, resulting in the gradual release of the spores from the capsule.

Arrest of peristome development can result in the loss of segments, cilia, teeth, the entire endostome or exostome, or the whole peristome. Stegocarpous mosses that lack a peristome, e. Although they lack a peristome at capsule maturity, such mosses, nonetheless, display characteristic peristomial layers in their developing capsules, and can be aligned with peristomate taxa using their peristomial formulae.

Most mosses are isosporous, meaning that spore sizes are unimodal, with variation ranging around one arithmetic mean G. Mogensen Some dioicous mosses that produce dwarf males, however, are anisosporous D. Vitt In this case, half of the spores in any capsule are significantly smaller than the other half, that is, spore sizes are bimodal within a single capsule H.

Ramsay Culture studies have documented that in many taxa the small spores germinate later than the large spores and give rise to dwarf males M. Ernst-Schwarzenbach Bimodality of spore sizes does not, however, always correlate with sexual dimorphism.

In some instances, the small spores are consistently abortive, a condition termed pseudo-anisospory Mogensen Mogensen hypothesized that a lethal combination of alleles from two genes is responsible for the abortive spores and that this condition leads to balanced polymorphism in the taxon. Pseudoanisopory is more common than true anisospory and occurs in both dioicous and monoicous taxa.

Spores in the majority of mosses are dispersed as single cells, but precociously germinated multicellular spores occur in some xerophytes or epiphytes, such as Drummondia.

Spores are typically spheroidal, but may also be ovoid, reniform, or tetrahedral. Ornamentation of the outer spore wall comes primarily from the perine, which is formed from deposits of globular materials produced within the spore sac G. Mogensen , although in some taxa, e. McClymont and D. Larson In most cases the globular deposits of perine appear to be rather randomly deposited over the spore surface as granulose papillae, e.

Neidhart Variations in spore wall ornamentation have been little used in moss systematics, with the exception of a few groups that have been studied using SEM, e. Smith , Encalyptaceae D. Vitt and C. Hamilton , and Pottiaceae K. Saito and T. Hirohama ; J. Crandall-Stotler Sharon E. Bartholomew-Began With over 12, species recognized worldwide M.

Gametophyte Characters Spore Germination and Protonemata A moss begins its life cycle when haploid spores are released from a sporophyte capsule and begin to germinate. Shoot Morphology and Habit The leafy shoot continues to grow from mitotic activity of its obovoidal to fusiform apical cell and surrounding meristem. Rhizoids Except for Takakia and Sphagnum , mosses are anchored to their substrates by filamentous, often branched, reddish brown rhizoids.

Stem Anatomy In many mosses, the stem is anatomically complex, consisting of a differentiated epidermal layer, a cortex, and a central strand of thin-walled, hydrolyzed water-conducting cells, called hydroids Fig. Leaves The considerable variation that occurs in the arrangement and structure of moss leaves provides some of the most useful characters for species identification Figs. Variation in leaf morphology, anatomy and habit. Sexual Reproduction Gametangia are typically clustered with interspersed, sterile hairs, called paraphyses, at shoot or branch apices.

Sporophyte Characters Embryo Development Concomitant with growth of the embryonic sporophyte, cell divisions in the surrounding archegonial center, basal archegonial stalk, and subtending gametophyte shoot produce an enclosing epigonium. Seta Anatomy The seta and capsule continue to develop after the emergence of the sporophyte from the epigonium, the seta from a generalized, apical meristem and the capsule by patterned divisions in earlier formed capsule initials. Capsule Anatomy Mosses are monosporangiate, meaning that each sporophyte produces only a single sporangium, or capsule.

The Peristome In the majority of stegocarpous mosses, spore dispersal is mediated by the peristome, a circular system of teeth that is inserted on the mouth of the urn, to the inside of the operculum. Spores Most mosses are isosporous, meaning that spore sizes are unimodal, with variation ranging around one arithmetic mean G. Polytrichum or Dawsonia plants can be quite tall, with the free-standing stems of some species growing to over 60 centimetres in height.

Hence it is not surprising that people often mistake these mosses for herbaceous flowering plants. Though the stems in the Dawsoniaceae and Polytrichaceae are fairly firm, they contain no lignin and are not woody. There are essentially two growth forms for moss plants. In one the stems are basically erect, with just one upright stem per plant or with the initial erect stem producing some branches, depending on the species , giving the individual plant a tufty or shrubby appearance.

In the other growth form the moss will have mostly trailing stems. If the stems cling to the substrate the overall appearance, to the naked eye, will be of a creeping plant but in some species they hang, almost curtain-like, from branches. The trailing mosses are typically highly branched with the branches growing along the substrate - but many such species also produce short, upright branches.

Branches develop from surface cells in the originating stem and in most mosses branches are simple, single outgrowths from the originating stems. In Sphagnum you will see branches developing in fascicles.

Within such a fascicle, some of the branches will be stout and spreading, while others are slender and drooping. In species with an upright growth form the stems may be very short almost non-existent to quite long - as already noted for some Dawsonia species.

If there is only a very rudimentary stem the plant will look like a bunch of leaves growing from just a single point. In genera like Polytrichum and Dawsonia the individual plants are typically just single stems, with branching rare. Amongst the upright mosses there are the so-called "dendroid" mosses, which have a spread of branches atop a vertical stem. The word " dendroid " means "tree-like" and it's easy to see how apt that term is.

In some cases, instead of branches in all directions, there'll be a fan-like spread of branches. You'll also see such mosses called "umbrella mosses" - an equally apt descriptive expression. There are many erect-stemmed species of moss where the plants grow very closely together in mat-like or cushion-like colonies. You can see a somewhat cobblestone-like surface. If you take a very small sample from the colony and look at it side-on you see this.

What you see in the final photo is a small number of individual plants, packed together very tightly. Leptostomum macrocarpum , showing dead material below. In the case of the cushion-like growth, much of the cushion may be composed of dead material photo right. As the stems grow, the older leaves lower down on the stem die, leaving a living green layer atop a mass of brown, dead material.

That brown section will be a mix of rhizoids, dead leaves and stems, and other organic matter that may have been trapped by the plants making up the moss-cushion. You can still make out some leaves in that mass of brown. As the stems continue to grow, more and more dead material will accumulate. Such largely-dead cushions are more characteristic of moist areas, where they can grow to a considerable size.

It is common to see sizable green cushions, on rock or trees for example, in moist habitats. Instead of growing in cushions, you can also get simple-stemmed species where the plants grow separately from each other. Then they look like many small, green fingers poking up from the soil. The plants are spread vegetatively by rhizomes. The stems feel very rough, because the epidermal tissues are impregnated with tiny grains of silica sand.

This probably helps protect the plant against herbivores. The green plant we see is the diploid sporophyte generation. The stalks can be highly branched vegetative stalks, which actually look like horse tails, or straight unbranched reproductive stalks, which are tipped with a large strobilus containing the sporangia. The homosporous spores develop into a teeny-tiny green gametophyte, just a few mm long, that looks like the gametophyte of a fern.

The gametophyte is haploid, free-living, and autotrophic. Ferns probably evolved from the psilopsids, sometime in the Devonian, relatively early on in land plant evolution. They are very abundant and diverse, ranging in size from a single centimeter to trees 24 meters tall with 5 meter fronds. Ferns are relatively advanced plants, with true roots, stems and leaves.

The blade of the fern is called a frond, and the little individual leaflets are called pinnae. Ferns have true leaves, what botanists call macrophylls. While the leaves of more primitive plants, which are called microphylls, are simply extensions of the epidermis of the stem, the leaves of ferns and higher plants were formed as a web of tissue stretched between small terminal branches. The leaves of higher plants, as well as the modified leaves that make up the pine cone and the flower.

The life cycle of the fern is typical of other non-seed vascular plants. The leafy green plant is the sporophyte. Fertile fronds develops clusters of small sporangia on the underside of the frond.

These clusters of sporangia are called sori sing. Sori are often protected by a tiny umbrella-like cap called an indusium -ia. Ferns are mostly homosporous, though some are heterosporous.

The heterosporous state is a more advanced condition, that seems to have evolved independently in several groups of plants.

The haploid spores are formed by meiosis inside the sporangium. They are ejected in a miniature explosion caused by the unequal drying of the alternate thick and thin-walled cells that line the outer surface. The top pulls slowly back until it reaches a critical point and then snaps forward at an incredible speed. At that size scale, the expulsion of fern spores is one of the most explosive events in nature. The spores germinate into tiny gametophytes. Its small size lets it rely entirely on diffusion.

Its tiny rhizoids are associated with mycorrhizal fungi. The little prothallus is green, and photosynthetic, and bears either antheridia and archegonia, or sometimes both together, on its upper surface lab slides have both on same prothallus. The archegonia are always found at the arch of the heart, and the antheridia are tucked away among the tiny rhizoids at the other end.

The sperm swims to the egg to fuse into a diploid zygote. The new sporophyte grows directly out of the top of the gametophyte. When it first begins to uncurl, the frond looks like the scrolled neck of a violin or fiddle, and this stage of development is called a fiddlehead.

Examine the living lycopsids on display. Why are they called club mosses? Notice that quillworts and Selaginella are very different in appearance from the club mosses. Examine slides of Selaginella's strobilus. Identify megaspores and microspores.

Examine the living horsetails on display. Notice the prominent strobili of the reproductive stalks, and the bushy growth form of the vegetative stalks if available. Examine the living whisk ferns on display. Psilopsids have a simple dichotomous branching pattern. You may see tiny yellow sporangia on the branches. Whisk ferns lack strobili. These primitive plants are closely related to ferns. Examine the living ferns on display.

Can you see any fiddleheads? Look for the rhizomes. Rhizomes are modified horizontal stems bearing roots, that run along or just underneath the ground, and spread ferns and fern allies around. Examine the living fern prothallus on display under a dissecting microscope. Note its characteristic heart shape. Some prothalli may have a tiny new fern emerging from the notch of the "arch" heart, where the archegonia are located.

Examine the fern leaflet on display under the dissecting microscope. Notice the prominent indusia , and the small sporangia peeking out from beneath. You'll see a few groups of sporangia that have lost their indusium.