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. The plants absorb water and nutrients directly through these leaf-like structures. The seta plural, setae contains tubular cells that transfer nutrients from the base of the sporophyte the foot to the sporangium.
Shingles composed of wood, asbestos, and conglomerate composition all make suitable homes for moss; however, metallic roofs or those with an abundance of tar will discourage moss growth.
But the tarred roof must be smooth to assure that mosses will not colonize in the cracks and crevices. Mosses prefer to colonize shingles above the eaves, on detritus that builds up in the eaves' troughs or other depressions. Mosses will be at their best in the winter when there is plenty of water, little light, and low temperatures. In summer mosses dry out and become dormant.
What are mosses good for? Unknown to most of us, mosses actually have many uses, from ecological to medical with a suite of common household uses in between.
One of the better known ecological uses of moss is as bioindicators of air pollution, such as those caused by factory emissions. They are very good indicators of acid rain damage to an ecosystem as well. Mosses are also used as erosion control agents as they aid in moisture control and stabilization of soil that would either be wind blown or washed away by water. Mosses occupy an important ecological niche in arctic and subarctic ecosystems where moss symbionts provide most nitrogen fixation in these ecosystems, as compared to the leguminous associations that are responsible for this job in temperate regions.
Mosses can also be used as bioindicators of water pollution and treatment of wastewater. Throughout history mosses have been used in horticulture because they are beneficial to the soil. Mosses increase the amount of water soil can store and improve soil's nutrient holding capacity. In the United States mosses are not highly acclaimed for their use in gardening. But ornamental and garden uses of mosses are becoming more common. See the book Moss Gardening by George Schenk.
Each generation has a different physical form. The defining features of bryophytes are: Their life cycles are dominated by a multicellular gametophyte stage. Their sporophytes are unbranched. They do not have a true vascular tissue containing lignin although some have specialized tissues for the transport of water. Bryophytes are called plant kingdom amphibians even though these plants live in soil, and they require water for sexual reproduction.
But the benefits are more than sensory. Bryophytes mosses, liverworts and hornworts can reduce groundwater contamination, counteract erosion, curtail stormwater runoff and even reduce air pollution. Mosses may be small in size but they offer big options for greening our landscapes. General Characteristics of Bryophytes: The plant body is thallus like, i.
It is attached to the substratum by rhizoids, which are unicellular or multicellular. They have a root-like, stem-like and leaf-like structure and lack true vegetative structure. Unique features of bryophytes is that they have sporophytes attached to the gametophyte. The gametophyte is the dominant stage in the life cycle. The diploid sporophyte is attached to the gametophyte and is dependent on the gametophyte for development. Plant of algae is unicellular or simple multicellular in algae. A mature sporophyte makes spores, and the life cycle starts over again.
Gymnosperm means "naked seed," a name that reflects the fact that gymnosperms have no fruits to protect their seeds. These changes include:. First, the seed. What is a seed? A seed consists of an embryo and its food supply. Because a seed has a protective coating in the form of a seed coat, it can lie dormant for months or years until conditions are right for it to germinate.
An example of a gymnosperm seed is the pinyon pine below. Those round things in the middle are the seeds, with the remnants of a cone surrounding them.
Public domain image from National Park Service, retrieved from. Reduced gametophytes: We know gametophytes are essential for plant life cycles. In ferns, the gametophytes lived on their own, were photosynthetic, and were small compared to the sporophyte. In gymnosperms, the gametophytes are even smaller, only visible through a microscope.
There are also two kinds of gametophytes, bringing us to the next subject…. Heterospory: In seed plants, there is no one-size-fits-all spore. Instead, there are megaspores, which grow into female gametophytes, and microspores, which grow into male gametophytes. Each sporangium makes only one kind of spore, so the sporangia are either megasporangia or microsporangia. Where do we find these sporangia?
On pinecones! And because not every gymnosperm is a pine, we also find sporangia on cones of other species, such as firs, redwoods, and spruces.
You probably have spent much more of your life thinking about ice cream cones and sno-cones than plant cones. Male cones microstrobili hold microsporangia, and female cones hold megasporangia.
Male cones are temporary structures that exist only long enough to make and release pollen, but female cones can grow for years while the seeds they hold develop.
Here is a picture of male pine cones. See how small they are? Ovules: As we already established, a megasporangium produces a megaspore, and they are stuck on a spore-bearing leaf a sporophyll on the sporophyte. A layer of sporophyte tissue surrounds and protects the megasporangium and megaspore. This layer of tissue is called an integument.
The integument, the megasporangium, and the megaspore together make up the ovule. An ovule is where a female gametophyte develops and produces eggs. The integument will later give rise to the seed coat that protects the seed.
Pollen grains: Once the microsporangium produces a microspore, that microspore develops into a pollen grain that consists of a male gametophyte and a tough pollen wall that protects the gametophyte while the pollen grain disperses.
When a pollen grain lands in an appropriate place i. Sperm travel down this pollen tube into the ovule. If you get seasonal allergies, you can probably blame your runny nose and itchy eyes on the wind-pollinated plants that release their pollen into the air and straight into your nasal passages.
Just tell those plants that they would be better off finding animal pollinators and to leave you alone! Gymnosperms are wind pollinated, and some angiosperms, such as grasses, have evolved wind pollination even though their angiosperm ancestor was not wind-pollinated.
Why on earth would they do this? It turns out pollen is cheap to make, energetically speaking, especially compared to sugary nectar and showy flowers. So some plants have become successful by letting the wind do the work.
And if you think about where grasses live, in fields or open prairies, it seems likely that the pollen will land on the right spot. OK so where is all this pollen going? And what exactly is pollen, anyway? These in turn, bear gametes and spores. Put the two gametes together and…voila!
We get a zygote that develops into a sporophyte. All the angiosperms and gymnosperms are sporophytes when visible to the naked eye.
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