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By the end of this section, you will be able to:
  • Identify the main characteristics of bryophytes
  • Describe the distinguishing traits of liverworts, hornworts, and mosses
  • Chart the development of land adaptations in the bryophytes
  • Describe the events in the bryophyte lifecycle

Bryophytes are the group of plants that are the closest extant relative of early terrestrial plants. The first bryophytes (liverworts) most likely appeared in the Ordovician period, about 450 million years ago. Because of the lack of lignin and other resistant structures, the likelihood of bryophytes forming fossils is rather small. Some spores protected by sporopollenin have survived and are attributed to early bryophytes. By the Silurian period, however, vascular plants had spread through the continents. This compelling fact is used as evidence that non-vascular plants must have preceded the Silurian period.

More than 25,000 species of bryophytes thrive in mostly damp habitats, although some live in deserts. They constitute the major flora of inhospitable environments like the tundra, where their small size and tolerance to desiccation offer distinct advantages. They generally lack lignin and do not have actual tracheids (xylem cells specialized for water conduction). Rather, water and nutrients circulate inside specialized conducting cells. Although the term non-tracheophyte is more accurate, bryophytes are commonly called nonvascular plants.

In a bryophyte, all the conspicuous vegetative organs—including the photosynthetic leaf-like structures, the thallus, stem, and the rhizoid that anchors the plant to its substrate—belong to the haploid organism or gametophyte. The sporophyte is barely noticeable. The gametes formed by bryophytes swim with a flagellum, as do gametes in a few of the tracheophytes. The sporangium—the multicellular sexual reproductive structure—is present in bryophytes and absent in the majority of algae. The bryophyte embryo also remains attached to the parent plant, which protects and nourishes it. This is a characteristic of land plants.

The bryophytes are divided into three phyla: the liverworts or Hepaticophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.

Liverworts

Liverworts (Hepaticophyta) are viewed as the plants most closely related to the ancestor that moved to land. Liverworts have colonized every terrestrial habitat on Earth and diversified to more than 7000 existing species ( [link] ). Some gametophytes form lobate green structures, as seen in [link] . The shape is similar to the lobes of the liver, and hence provides the origin of the name given to the phylum.

 The illustration shows a variety of liverworts, which all share a branched, leafy structure.
This 1904 drawing shows the variety of forms of Hepaticophyta.
 Photo shows a liverwort with lettuce-like leaves.
A liverwort, Lunularia cruciata , displays its lobate, flat thallus. The organism in the photograph is in the gametophyte stage.

Openings that allow the movement of gases may be observed in liverworts. However, these are not stomata, because they do not actively open and close. The plant takes up water over its entire surface and has no cuticle to prevent desiccation. [link] represents the lifecycle of a liverwort. The cycle starts with the release of haploid spores from the sporangium that developed on the sporophyte. Spores disseminated by wind or water germinate into flattened thalli attached to the substrate by thin, single-celled filaments. Male and female gametangia develop on separate, individual plants. Once released, male gametes swim with the aid of their flagella to the female gametangium (the archegonium), and fertilization ensues. The zygote grows into a small sporophyte still attached to the parent gametophyte. It will give rise, by meiosis, to the next generation of spores. 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 (shown in [link] )—are splashed out of the cup by raindrops. The gemmae then land nearby and develop into gametophytes.

Questions & Answers

what do we mean by transgenic organisms?
FADILAT Reply
what is or are the functions of the Islets of Langarhaans
FADILAT
They are the regions of the pancreas that contains the endocrine cell
Iyadi
is the studly of life
Aisha Reply
what is biology
Asunta Reply
what is soil
Mukisa Reply
the top layer of the earth in which plant's, tree's
Ahmad
type of soil
Asunta
function of cell wall
Nthati Reply
function of cell wall
Asunta
To protect the cell from bursting
Maurice
to protect the cell from bursting
Deborah
What is escherichia coli
Tumise Reply
in what type of cells is meiosis taking place?
Rhyeann Reply
sex cells
Eric
hlo
Amit
reproductive system of earthworm plzz describes
Amit
applications of biology
Namawejje Reply
what is dormancy?
Aliyu Reply
hello guys what's the difference between prokaryotes and eukaryotes
Nwachukwu Reply
hlo what are the applications of biology?
Namawejje
eukaryotic cells have DNA in their nucleus while prokaryotic cells have their DNA present freely in their cytoplasm.
FADILAT
deviation from mendelian
Ogali Reply
what is lethal allele
Ogali
Explain how chemical , bioligical and physical interaction between themselves and the non living components ?
Beyan Reply
what is Tissues
Faith Reply
Group of similar cells performing some related functions We have some type of tissues Connective Muscle Epithelial Nervous tissues
peter
group of cells that is called tissue.
Nikita
tissue is the arrangement or combination of similar cells that perform the same function .
FADILAT
what is abiotic?
Williams Reply
state 2 abiotic factors that affect the rate of transpiration in plants?
Benenge
non living things
Chris
1) temperature:the temperature of the atmosphere affects the opening and closing of the stomata in the leaves of plants .high temperature encourages water loss . 2)wind : air flow encourages transpiration in plants . example,plants that are found on high areas like mountains transpire easily
FADILAT
I agree with Fadilat Muhammad In addition, water plants tend to reserve water during dry seasons so if they are not given plenty of water, they keep the water to them selves
Iyadi
what is a cell
Esther Reply
structural and functional group is called cells
Nikita
the structural and functional unit of life is called cell. the cell was discovered by Robert hook in 1665Ad.
ROHIT
The structural functional of unit is called cell
Anas
The structural and functional unit of cell
Anas
Halim I am. A biological cell is the basic unit of life made up of protoplasm, organelles, a mitochondria where ATP, adenosinetriphosphate produces our energy, and a membrane barrier that envelopes the entire cell separating the internal and the external like our epidermis skin.
halim
is isn't the cell
Amarachi
cell is the functional unit or basic unit of life
Deborah
hello.the cell is defined as the basic structural and functional unit of life.it is responsible for the information and activities of an organism.
FADILAT
Robert Hooke discovered cells while observing the bark of a tree under a microscope.the name CELL was given to the tiny structures or compartments because they looked like the cells of monks
FADILAT

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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