As an aside, liverworts, which are related to mosses, sometimes resemble wet lichens, but never mind that for now! That is an interesting way to describe lichens. As a horticulturist, I do not give it much though. I just dismiss them as lichens. I am more interested in moss. It is sort of like how entomologists can dismiss spiders. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account.
Notify me of new comments via email. Notify me of new posts via email. Search for: Search. Oak Moss, Evernia prunastri , is actually a lichen. Image: R. Mosses come in many different forms. Mosses come in two basic types, a cushiony type, 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 plants, with antheridia at the top of the plant, or female plants, with archegonia at the top.
Remember that these gametophytes are always haploid 1N plants. Sperm are produced within each antheridium , and an egg in each archegonium. Because the plant is already haploid, these gametes can be created by mitosis, simple cell division. The sperm swims to the archegonia through a thin film of water, drawn by a chemical attractant produced by the female plant, then swims down the neck of the archegonia to the egg. A good morning dew is more than sufficient water for the sperm to swim.
Once 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 later turns brown and becomes essentially a parasite on the female gametophyte. The sporophyte plant consists of a stalk, and a small capsule on the top. Within the capsule, cells undergo meiosis to produce tetrads of haploid spores. When the capsule is ripe, its hinged lid or operculum opens up, and the spores are quickly dispersed by wind and water. The spores germinate into a tiny green thread, which looks like a simple strand of green algae.
This similarity is one more clue that bryophytes are descended from green algae. The new adult gametophytes grow from a tiny bud that develops on the protonema. Eventually these gametophytes will grow to produce gametes, and the whole cycle will start over again. Mosses can also reproduce asexually by fragmentation or by growing little vegetative buds called gemma, which can 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.
Peat also contains other plants such as reeds, that grow amid the sphagnum. In dried form, 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 times its dry weight, dried sphagnum can absorb 20 times its own weight in fluids!
Peat bogs are very important and interesting ecosystems. Division Hepaticophyta - 9, sp. Liverworts have the simplest bodies of all the green plants. The gametophyte, the dominant stage, looks like a flat scaly leaf, with prominent lobes.
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.
Can you guess what walnuts were supposed to cure? Liverworts share the general properties of bryophytes, but are not very closely related to mosses or hornworts.
Many botanists think they may have evolved independently, from a different group of green algae. If you get the aquatic liverwort Porella in lab, take a sniff of the jar, but not too deep! It smells of rancid oils, oils that went a little funky while the plant was being shipped.
Another characteristic unique to liverworts is their lack of stomata, which are found in all other plants, including mosses and hornworts. In many species of liverworts, such as Marchantia , the one you will most likely see in lab, the antheridia and archegonia are not on top of the plant, but hanging down from the underside of odd little structures that look like tiny umbrellas.
These umbrella-shaped structures are called the antheridiophore and archegoniophore. The bi-flagellated sperm swims to the egg, and fertilization takes place to form a diploid 2N zygote. The tiny diploid sporophytes, which remain attrached to the parent plant, have a very simple 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 around in a way that scatters the spores in all directions. Liverworts can also reproduce asexually by means of special structures called gemmae cups.
These little cups can be easily seen on the surface of the plant. Each gemma cup contains a number of tiny plantlets called gemmae, and a single drop of water will disperse them. 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 look like a little upright horn. Like mosses, hornworts have 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. Division Hepaticophyta - liverworts Marchantia, Conocephalum, Porella; fr. Examine the living mosses on display.
Notice the small capsules on top of the tiny sporophytes. Mosses generally grow in one 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 protonema. What type of algae does it remind you of? This resemblance is additional evidence that green algae gave rise to all higher plants. Examine the terrestrial liverworts Marchantia and Conencephalum one or both should be on display.
How does their growth habit differ from that of the mosses? Can you see any gemmae cups on the upper surface of these plants? Examine the aquatic liverworts like Porella and Riccia one or both should be on display. Notice how they differ from the more terrestrial forms of liverwort. Look at the preserved liverworts , and observe their distinct reproductive structures they look like little green umbrellas.
How does their life cycle differ from mosses? Hint: Be sure you 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. Just as the evolution of spores was the key to the invasion of the land surface by bryophytes, the invention of complex vascular tissues let tracheophytes complete the conquest of dry land.
There are about , species of vascular plants, grouped in nine 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 conduct food, water, and nutrients throughout the plant. While all plants need water, mosses and bryophytes need droplets of water to enable their haploid reproductive cells to combine. They are all known as the bryophytes.
Mosses Let's start with mosses. These are waxy little plants with no leaves and no stem that use each other to stay upright. Their inability to stay up is why you never see one little moss plant; it's always a group. That grouping also helps them retain water in the area. A waxy covering across their bodies helps keep water from evaporating. You will usually find them in moist areas out of the direct sunlight.
Good Worts We'll cover liverworts and hornworts together.
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