Liverworts Can Reproduce Asexually via Fragmentation or Gemmae Cups.
Lab 8 - Primitive Plants - Bryophytes, Ferns and Fern Allies
Introduction to Bryophytes - Mosses, Liverworts, and Hornworts
As we laissez passer from mosses to ferns, we see a gradual transition from primitive to modern traits. There are two major trends you should focus on in today's lab. The first is a transition in life cycles, the second is a change in bones internal structure.
Commencement, all plants undergo an alternation of generations, between a haploid gametophyte phase and a diploid sporophyte stage. In the nigh archaic plants, like mosses, the gametophyte is dominant (i.eastward. it'south big and dark-green). In higher plants like ferns and fern allies, the sporophyte stage is dominant. Gametophytes produce gametes (sperm and eggs) in a special structure called a gametangium (-ia), while sporophytes produce spores in a special structure called a sporangium (-ia).
2nd, all plants demand to get water to their cells. Primitive bryophytes like mosses and liverworts are so modest that they tin rely on diffusion to move water in and out of the plant. Mosses take a few strands of water conducting tissue in their central stem, but nothing like the large and well organized network of tubes in tracheophytes, or "tube plants". The vascular tissues in the more advanced ferns and "fern allies" are made upwards of xylem and phloem, which conduct h2o, nutrients, and food throughout the plant body. We'll expect at these tissues in a later lab.
Bryophytes besides need a moist environment to reproduce. Their flagellated sperm must swim through water to reach the egg. Then mosses and liverworts are restricted to moist habitats. There are no mosses in the desert. But mosses are surprisingly resistant to drying up, and can survive under very harsh conditions. Mosses are the about arable plants in both the Chill and the Antarctic. Asexual reproduction in bryophytes is accomplished by fragmentation or by tiny vegetative "sprouts" called gemmae, which class in special little structures called gemmae cups.
Mosses and liverworts are lumped together as bryophytes, plants lacking truthful vascular tissues, and sharing a number of other primitive traits. They likewise lack true stems, roots, or leaves, though they have cells that perform these general functions. The leafy green plant that we see when we look at a moss or a liverwort is really the gametophyte, which is the dominant stage in all bryophytes. The sporophytes of bryophytes do not take a free-living existence. They abound directly out of the fertilized egg in the archegonia, and remain dependent on the parent gametophyte for their nutrition.
Characteristics of Divisions
Division Bryophyta - (9,500 sp.) - mosses, Mnium, Sphagnum
Mosses come up in two basic types, a cushiony blazon, with erect stalks, and a feathery type, which forms flattened mats of low-lying and highly branched moss plants. In both cases, the leafy green gametophytes are dioecious They can be male person plants, with antheridia at the elevation of the plant, or female person plants, with archegonia at the acme. Remember that these gametophytes are always haploid (1N) plants.
Sperm are produced inside each antheridium, and an egg in each archegonium. Because the plant is already haploid, these gametes tin can be created past mitosis, unproblematic cell division. The sperm swims to the archegonia through a thin film of water, drawn by a chemic attractant produced by the female plant, and then swims downward the neck of the archegonia to the egg. A skilful morning dew is more than than sufficient h2o for the sperm to swim. In one case the sperm enters the archegonia, it fuses with the egg. The 2N zygote develops into a diploid sporophyte plant, a small stalk that grows directly out of the top of the archegonium. This stalk is initially green, and photosynthetic, but after turns brown and becomes essentially a parasite on the female gametophyte.
The sporophyte institute consists of a stalk, and a small sheathing on the meridian. Within the capsule, cells undergo meiosis to produce tetrads of haploid spores. When the sheathing is ripe, its hinged lid or operculum opens up, and the spores are quickly dispersed by air current and water. The spores germinate into a tiny green thread, which looks like a simple strand of green algae. This similarity is one more inkling that bryophytes are descended from green algae. This early threadlike phase is called the protonema (= first thread, plural = protonemata, similar stigma/stigmata). The new adult gametophytes grow from a tiny bud that develops on the protonema. Eventually these gametophytes volition abound to produce gametes, and the whole cycle will beginning over once more. Mosses tin also reproduce asexually by fragmentation or past growing little vegetative buds chosen gemma, which tin break off and grow into a new plant .
While bryophytes in general are more interesting than important, in the usual sense, a conspicuous exception are mosses of the genus Sphagnum. Sphagnum moss forms dense mats which become compressed into peat, which can be used equally fuel, although it's very smoky. Peat too contains other plants such as reeds, that grow amid the sphagnum. In stale class, peat moss is remarkably absorbent and, and has been used for diapers, for enriching poor garden soils, and as a field dressing for wounds. Whereas cotton absorbs iv-6 times its dry out weight, stale sphagnum can absorb 20 times its own weight in fluids! Peat bogs are very important and interesting ecosystems. Sphagnum mosses greatly increase local acidity by releasing H+ ions, and the pH of peat bogs tin can driblet to 4 or lower, perhaps the most acidic natural environment. Peat bogs cover nearly 1% of the Earth's land surface, an area about half the size of the U.s.a..
Segmentation Hepaticophyta - (9,000 sp.), liverworts, Marchantia, Conocephalum, Porella
Liverworts have the simplest bodies of all the greenish plants. The gametophyte, the ascendant stage, looks like a flat scaly leafage, with prominent lobes. It looks for all the earth similar a tiny flattened liver, hence the scientific name hepatico-phyta = liver institute. During the Middle Ages, this similarity caused physicians to prescribe liverwort for diseases of the liver. According to the Doctrine of Signatures the Creator had designed all of nature, including plants, with our welfare in mind. People believed that plants had been intentionally designed to resemble the organs of the body they were supposed to heal! Hence liver-wort, wyrt being the Anglo-Saxon word for herb. The shape of the liverwort was the signature of the Creator in nature. Tin you guess what walnuts were supposed to cure ? (diseases of the brain)
Liverworts share the general backdrop of bryophytes, just are not very closely related to mosses or hornworts. Many botanists recollect they may have evolved independently, from a unlike group of green algae. For one thing, liverworts don't store nutrient as starch but as oils. If you get the aquatic liverwort Porella in lab, have a sniff of the jar, but not too deep! It smells of rancid oils, oils that went a piddling funky while the plant was being shipped. Some other characteristic unique to liverworts is their lack of stomata, which are constitute in all other plants, including mosses and hornworts.
In many species of liverworts, such as Marchantia, the one you will most probable see in lab, the antheridia and archegonia are not on top of the constitute, but hanging down from the underside of odd little structures that look like tiny umbrellas. (These umbrella-shaped structures are chosen the antheridiophore and archegoniophore). The bi-flagellated sperm swims to the egg, and fertilization takes identify to form a diploid (2N) zygote. The tiny diploid sporophytes, which remain attrached to the parent plant, have a very unproblematic structure. Meiosis within the sporophyte produces a number of haploid spores. These spores are surrounded by curious long and twisted moist cells called elaters. When the capsule dries and bursts, the elaters twist and jerk effectually in a way that scatters the spores in all directions. Liverworts tin also reproduce asexually by ways of special structures called gemmae cups. These little cups can be hands seen on the surface of the plant. Each gemma loving cup contains a number of tiny plantlets called gemmae, and a unmarried drop of water will disperse them. These petty vegetative "clones" will then grow into a new gametophyte.
Division Anthocerophyta - (100 sp.), hornworts, Anthoceros
The green gametophytes of the hornwort look very much like a liverwort. But their small sporophytes more closely resemble those of mosses. The sporophytes grow out of the gametophyte, and await like a niggling upright horn. Similar mosses, hornworts take stomata, and so are probably more closely related to mosses and other plants than to the liverworts they mat resemble. These plants are symbiotic with the cyanobacteria Nostoc. The cyanobacteria fixes nitrogen for the hornwort.
Taxonomy
Kingdom Plantae
Bryophytes
Partition Bryophyta - mosses (Mnium, Sphagnum; fr.Gr. bryon = moss)
Division Hepaticophyta - liverworts (Marchantia, Conocephalum, Porella; fr.Gr. hepato = liver)
Division Anthocerophyta - hornworts (= Anthocerotophyta; Anthoceros; fr.Gr anthos = flower, keras = horn)
Terms
- alternation of generations
- gametophyte
- gametangium (-ia)
- archegonium (-ia)
- antheridium (-ia)
- sporophyte
- sporangium (-ia)
- spore
- capsule
- protonema
- vascular arrangement
- gemmae
- gemmae cup
To Do and View
Examine the living mosses on display. Notice the small capsules on top of the tiny sporophytes. Mosses more often than not grow in 1 of two growth types: cushiony moss and feathery moss.
Examine slides of the antheridia and archegonia. The sausage shaped antheridia produce sperm, and the flask shaped archegonia produces eggs.
Examine slides of the moss capsule, and identify the spores.
Examine slides of the protonema. What type of algae does information technology remind you of? This resemblance is additional evidence that greenish algae gave rise to all higher plants.
Examine the terrestrial liverworts Marchantia and Conencephalum (one or both should exist on display). How does their growth addiction differ from that of the mosses? Can you encounter any gemmae cups on the upper surface of these plants?
Examine slides of the liverwort Marchantia.
Examine the aquatic liverworts like Porella and Riccia (one or both should be on brandish). Notice how they differ from the more than terrestrial forms of liverwort.
Await at the preserved liverworts, and discover their distinct reproductive structures (they wait like little greenish umbrellas). How does their life cycle differ from mosses?
Examine slides of the hornwort Anthocerophyta.
Things to Remember
Know the life cycle of the moss in detail, and be able to recognize the diverse stages.
Hint: Be sure y'all understand the general life cycle of plants, and can tell which stages are haploid gametophytes (1N) or diploid sporophytes (2N). We'll learn several life cycles in lecture and in lab (moss, fern, pine, flowering plant), but all of them are variations on the same basic theme.
Ecological, Evolutionary, and Economic Importance
Mosses are important in landscaping and gardening, particularly peat moss (Sphagnum).
Peat moss (Sphagnum) has been used historically every bit dressings for wounds.
Peat moss can exist used every bit fuel.
Mosses are the most primitive living land plants.
Hornworts incorporate symbiotic colonies of the blue-green alga Nostoc.
shining club moss
Introduction to Tracheophytes - Ferns and Fern Allies
Tracheophytes (vascular plants) completed the conquest of the earth'southward surface begun by the more than archaic bryophytes. Just as the evolution of spores was the key to the invasion of the country surface by bryophytes, the invention of circuitous vascular tissues let tracheophytes complete the conquest of dry land. At that place are near 250,000 species of vascular plants, grouped in 9 divisions. Tracheophytes all have a well developed root-shoot system, with highly specialized roots, stems, and leaves, and specialized vascular tissue (xylem and phloem) that function like miniature tubes to acquit food, water, and nutrients throughout the plant. Because ferns and fern allies posses true vascular tissues, they can grow to be much larger and thicker than the bryophytes.
The ferns and fern allies (not-seed tracheophytes) mark two major evolutionary strides. In these and in all more avant-garde plants, the leafy green diploid sporophyte at present becomes the dominant stage. The tiny gametophyte may be either autotropophic (similar the fern prothallus) or heterotrophic (similar the gametophytes of some lycopsids), and is mostly free living and independent of the parental sporophyte. Unlike the vascular sporophytes, the gametophytes have no vascular tissue at all. These gametophytes are therefore very small, and develop best in moist areas, where they can absorb water directly from their surroundings.
Like the bryophytes, ferns and fern allies are still restricted to moist habitats. Their flagellated sperm need a thin movie of h2o to swim between the antheridium and the archegonium. And when the infant sporophyte grows upwards from the gametophyte, it is exposed to desiccation (drying upwardly). This basic strategy of a free-swimming sperm and a non-motile egg is shared by plants, animals, and algae. It makes sense, considering it means only one gear up of gametes has to make the perilous journey outside of the organism.
footing pine (Lycopodium) showing strobili
The ferns and fern allies germinate from spores. These plants are mostly homosporous - their spores are identical and you can't differentiate which will grow into male or female person plants. They are also monoecious - both the archegonia and antheridia (male and female reproductive structures) are borne on the aforementioned found. Contrast these archaic vascular plants with the more advanced seed plants, the gymnosperms and angiosperms, which germinate from seeds rather than from spores. Seed plants are all heterosporous. It is easy to differentiate the larger female person megaspore from the smaller male microspore. The sperm of seed plants have no flagella. They lack antheridia, and simply a few notwithstanding have an archegonia. Different the more archaic ferns and fern allies, seed plants are mostly dioecious, having separate male person and female plants.
In many of these primitive plants, sure leaves are specialized for reproduction. These modified leaves, or sporophylls, carry the sporangia at their bases. These sporophylls usually co-operative out from a shortened stem, forming a club shaped structure called a strobilus. The pine cone and the flower are elaborate variations on these primitive strobili.
There are four divisions of not-seed tracheophytes, vascular plants that reproduce by means of spores, the Psilophyta, Lycophyta, Sphenophyta, and Pterophyta. Before these non-seed tracheophytes evolved, the bryophytes were the dominant form of plant life. The evolutionary border of having a more efficient conducting organisation, and a well-adult root-shoot arrangement enabled them to outcompete bryophytes. If you're lucky enough to see footing pine or other club mosses growing in the shade of a large pine tree, think for a moment near how these tiny plants were once the masters of the planet, forming vast forests with trunks from 20 to 100 feet tall!
Taxonomy
Kingdom Plantae
Tracheophytes (vascular tissue, no seeds)
Segmentation Lycophyta - social club moss, quillworts (Lycopodium, Selaginella)
Division Sphenophyta - horsetails (Equisetum; fr.Fifty. equus = horse)
Division Psilophyta - whisk fern (Psilotum)
Division Pterophyta - true ferns (Pteris; fr.Gr. pteridion = little wing)
Terms
- homosporous
- heterosporous
- megaspores
- microspores
- rhizomes
- sporophylls
- strobilus (-i)
- sori
- indusium (-ia)
- prothallus
- fiddleheads
Partitioning Psilophyta - (fr Gr. psilo = polish), whisk ferns, Psilotum
There are only two living genera of whisk ferns, sole survivors of a big and widespread group of early land plants. In addition to the living Division Psilophyta, the psilopsids, there are two extinct divisions of primeval vascular plants. The primitive whisk ferns resemble these extinct pioneers in many ways. They are the only living vascular plants that lack a root-shoot organization, a feature they share with both extinct Divisions of bequeathed vascular plants. Some recent molecular evidence suggests that 1, or fifty-fifty both, of the living genera of psilopsids may actually be more closely related to ferns, like a fern that has reverted to more primitive traits. If this is true, and then Psilophyta will join the ranks of the numerous extinct Divisions of plants.
Psilopsids are found in tropical and subtropical areas, and occurs throughout the southern US. I once establish i growing on my back porch nether the leaves of a spider plant. Whisk ferns are a mutual weed in greenhouses all over the globe. They are simple green upright stems, with dichotomous branching. They have no leaves, and no truthful roots. The outer tissues of the stem do all the photosynthesizing. A portion of the stalk called a rhizome runs along the footing, or just beneath it. A rhizome is a horizontal stem that spreads the plant effectually. Roots grow out the lesser of the rhizome, and a new plant can arise at the same signal from the top.
The green stem-like plant is the diploid sporophyte, the dominant phase in the life cycle. In the small sporangia (bright yellow) that form along the upper stems, the spore mother jail cell forms haploid spores by meiosis. Their gametophytes are tiny trivial thread-like underground plants that lack chlorophyll, and live as heterotrophs in the soil, looking and interim much like a tiny fungi. It actually contains a symbiotic fungi, the same mycorrhizae that live in the rhizomes of the developed sporophyte.
Division Lycophyta - (1,000 sp., fr. Gr. lycos=wolf), club mosses, quillworts, Lycopodium (podus=foot)
Their are only five living genera of lycopsids, but at one fourth dimension from the afar Devonian, about 400 mya, well into the Carboniferous, they were the dominant grade of vegetation on the confront of the World. Now they are reduced to a shadow of their glorious past, inconspicuous little plants in the woods understory. The tropical species are small epiphytes (plants that abound on other plants).
Their roots abound from special underground stems chosen rhizomes, as do about of these archaic tracheophytes. In some species the sporophylls are mixed in with the calibration-like leaves. In many species, the sporophylls are organized into strobili, hence the common proper name of "club moss". The sperm swim downwardly the strobilus to the archegonia, and the zygote that forms is retained in the cone, which ripens and falls to the basis. The gametophytes are independent and free-living, They are curious creatures that look and deed cypher similar their sporophyte parents. They tin can be either heterotrophic or autotrophic, and commonly accept a symbiotic fungi associated with them. Many of the lycopsids are heterosporous. Selaginella is a good case of a heterosporous plant.
Division Sphenophyta - (xv sp., one genus, fr. Gr. sphen=wedge), horsetails, Equisitum
In waste places, disturbed areas like trails and railroad beds, and in odd corners of fields and forests you might notice another small constitute quietly dreaming of its former splendor, the horsetail. Horsetails appeared in the late Devonian, and were among the dominant forest copse for hundreds of millions of years. Only one genus of Sphenophyta still exists, the genus Equisetum, and it may be the oldest living genus of plants on earth. Horsetails towered amongst the Carboniferous forests, reaching heights of 30-60 feet. Much of the coal deposits we exploit for fuel today were formed from horsetails and other trees during the Carboniferous, toward the finish of the Paleozoic.
Horsetails take true roots, stems, and leaves, though the leaves are piddling more than flattened stems. Their hollow, ribbed stems are jointed, kind of similar a stalk of bamboo, and a roll of leaves arises at each joint. The plants are spread vegetatively past rhizomes. The stems feel very rough, because the epidermal tissues are impregnated with tiny grains of silica (sand). This probably helps protect the constitute against herbivores. These crude stems made this plant ideal for pioneer women to use for scrubbing pots and pans, hence its other common proper noun, "scouring rush".
The green found we see is the diploid sporophyte generation. The stalks can exist highly branched vegetative stalks, which actually look similar horse tails, or direct unbranched reproductive stalks, which are tipped with a big 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, gratis-living, and autotrophic.
Division Pterophyta - (12,000 sp., fr. Gr. pteridion=piddling fly), ferns
Ferns probably evolved from the psilopsids, onetime in the Devonian, relatively early on in land establish evolution. They are very abundant and diverse, ranging in size from a single centimeter to trees 24 meters tall with 5 meter fronds. Ferns accept been amend competitors with seed plants than other seedless vascular plants, and are a conspicuous part of the mural throughout the world, but peculiarly in the tropics, where 75% of their 12,000 species occur.
Ferns are relatively advanced plants, with truthful roots, stems and leaves. The blade of the fern is called a frond, and the little individual leaflets are chosen pinnae. Ferns have truthful leaves, what botanists call macrophylls. While the leaves of more primitive plants, which are called microphylls, are but extensions of the epidermis of the stem, the leaves of ferns and higher plants were formed as a spider web of tissue stretched betwixt small-scale terminal branches. The leaves of college plants, as well as the modified leaves that make upwards 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. sorus). 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 avant-garde status, 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 diff drying of the alternate thick and thin-walled cells that line the outer surface. The top pulls slowly back until it reaches a critical bespeak 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. The little heart shaped gametophyte is called a prothallus, literally "first-body" (pl prothalli). the prothallus has no vascular tissue. Its modest size lets information technology rely entirely on improvidence. 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 elevation of the gametophyte. When it first begins to uncurl, the frond looks similar the scrolled cervix of a violin or fiddle, and this phase of development is chosen a fiddlehead.
To Do and View
Examine the living lycopsids on brandish. Why are they chosen club mosses? Discover that quillworts and Selaginella are very dissimilar in appearance from the club mosses.
Examine slides of Selaginella's strobilus. Identify megaspores and microspores.
Examine the living horsetails on display. Discover the prominent strobili of the reproductive stalks, and the bushy growth grade of the vegetative stalks (if available).
Examine the living whisk ferns on brandish. Psilopsids have a simple dichotomous branching pattern. You may run across tiny yellow sporangia on the branches. Whisk ferns lack strobili. These primitive plants are closely related to ferns.
Examine the living ferns on display. Tin you see any fiddleheads? Expect for the rhizomes. Rhizomes are modified horizontal stems bearing roots, that run forth or simply underneath the ground, and spread ferns and fern allies around.
Examine the living fern prothallus on display nether 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 slides of the prothallus: Find the archegonia (tin y'all see an egg?).
Examine the fern leaflet on display nether the dissecting microscope. Notice the prominent indusia, and the modest sporangia peeking out from beneath. You'll see a few groups of sporangia that have lost their indusium. If you're lucky, equally the heat of the microscope dries out the leaflet, you lot might run into the sporangia squirt its spores. But don't blink - it's one of the fastest and most explosive acts in nature. Use high power to observe the spores.
Examine slides of the sori and indusia; use loftier ability to find the spores.
Things to Remember
Know the life cycle of the fern. Recognize specimens and slides of the various stages.
Economic, Ecological, and Evolutionary Importance
Ferns and fern allies are primarily responsible for our modern deposits of coal.
The fiddleheads of some species of ferns are edible.
Ferns are important for the florist, gardening and landscape industries.
Consider This
Why are all these plants restricted to wet habitats?
Which group of protists gave ascent to these plants? (How exercise nosotros know?)
Why is the epidermis of the horsetail and so crude? What does information technology demand protection from?
All of the fern allies in this lab in one case towered 50-100 feet or more. What happened?
Links to Explore
Bryophyte taxonomy, images, and more at:
http://bryophytes.plant.siu.edu/
Go info about bryophytes from the Missouri Botanical Garden at:
http://www.mobot.org/mobot/tropicos/nigh/
Lie down amidst the ferns at the American Fern Society, try their lengthy list of links:
http://amerfernsoc.org
Basic info on ferns and fern allies, complete with images, courtesy of Texas A&M:
http://world wide web.csdl.tamu.edu/FLORA/fsb/fsbfern1.htm
Look for ferns on the "tree of life" at
http://phylogeny.arizona.edu/tree/eukaryotes/green_plants/embryophytes/filicopsida/filicopsida.html
Acquire well-nigh the part of ferns in forest ecology at:
http://www.cciw.ca/eman-temp/reports/publications/Mixedwood/ferns/intro.htm
Detect photos and more of ferns and fern allies at:
http://www.botany.hawaii.edu/faculty/carr/nfpfamilies.htm
Good bones info on non-flowering plants, with not bad pictures at:
http://www.phytology.hawaii.edu/faculty/carr/equiset.htm
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Source: http://www.tulane.edu/~bfleury/diversity/labguide/mossfern.html
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