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14.2 Seedless Plants
The flowering plants, or angiosperms, which protect their seeds inside chambers at the center of a flower, are the most successful plants.
The walls of these chambers become fruits.
The major divisions of plants are shown in the table.
There are a lot of seedless plants in the landscape.
There are mosses on tree trunks and horsetails on the forest floor.
Only a small portion of the plants in our environment are seedless.
Three hundred million years ago, seedless plants dominated the landscape and forests of the Carboniferous period.
Large deposits of coal were created by their decomposing bodies.
The close relative of early terrestrial plants are the ryophytes.
The first bryophytes probably appeared about 490 million years ago.
The lack of lignin in the stems of plants and other resistant structures makes it hard for bryophytes to form fossils.
The Silurian period (450 million years ago) saw the spread of plants throughout the world.
The Silurian period must have started with this fact.
There are about 18,000 species of bryophytes, which thrive mostly in damp habitats.
They are the major flora of environments like the tundra, where their small size and tolerance to desiccation give them advantages.
They don't have the specialized cells that conduct fluids found in the plants.
Water and nutrients can be found inside conducting cells in bryophytes.
Bryophytes are often referred to as nonvascular plants.
All the vegetative organs are part of the haploid organisms.
The diploid sporophyte is not noticeable.
The gametes swim using flagella.
The multicellular sexual reproductive structure is present in bryophytes.
The embryo is attached to the parent plant.
This is a characteristic of land plants.
In plants, the bryophytes are divided into three divisions: the liverworts, the hornworts, and the mosses.
Many habitats on Earth have been colonized by the lyctoms.
The origin of the common name given to the division can be found in the shape of the liver.
The organisms in the picture are in the gametophyte stage.
There are a lot of hornworts.
The short, blue-green gametophyte is the dominant phase of the life cycle of hornworts.
The defining characteristic of the group is the sporophyte.
Hornworts grow tall and slender.
The main vegetation in the tundra is the main vegetation in the understory of tropical forests.
The shallow rhizoids in the tundra allow them to grow without digging into the frozen soil.
They provide shelter for small animals and food for larger animals, and slow down erosion.
Mosses are used to monitor the quality of air.
The sensitivity of mosses to copper salts makes them a common ingredient of compounds marketed to eliminate mosses in lawns.
The most prominent group of land plants are the vascular plants.
More than 90 percent of Earth's vegetation is comprised of 275,000 species of vascular plants.
Evolutionary innovations explain their success.
The first fossils that show the presence of tissue are from the Silurian period.
There is a pattern of xylem at the center of the arrangement of cells.
The phloem cells are divided into sieve elements.
The xylem and phloem tissues form the vascular system of plants.
It seems that the roots are not well preserved in the fossil record, but they did appear later in evolution.
A new feature of plants was the development of an extensive network of roots.
The bryophytes were attached to the rhizoids.
They didn't provide a strong anchor for the plant and they didn't absorb water or nutrients.
Water and minerals are transferred from the soil to the rest of the plant by the roots.
The extensive network of roots that penetrate deep in the ground to reach sources of water also helps trees by stabilizing them.
Mycorrhizae is formed by a symbiotic relationship between roots and fungi.
This increases the surface area for absorption.
The appearance of true leaves improved the efficiency of the photosynthetic process.
The leaves increase their surface area.
The leaves play an important role in the life of plants.
The leaves were modified to bear sporangia.
For example, the pine cones of pine trees are commonly known as cones.
Plants had evolved well-defined leaves and root systems by the Late Devonian period.
Plants increased in size and height.
Most of the land was covered with swamp forests of club mosses and horsetails during the Carboniferous period.
The Carboniferous was named after the extensive coal deposits in these forests.
The sporophyte was the dominant phase of the lifecycle in seedless plants.
Water is still required for fertilization of seedless plants.
Club mosses, horsetails, and whisk ferns are modern-day seedless plants.
They dominated the landscape of the Carboniferous period, growing into tall trees and forming large swamp forests.
The horsetails are a third group of plants in the Pterophyta.
They are survivors of a large group of plants that produced large trees and swamp forests in the Carboniferous.
The name Arthrophyta means "jointed plant" and refers to the stem of a horsetail.
The leaves and branches come out.
There are thin leaves on the horsetail plant.
Ferns are considered to be the most advanced seedless plants.
The leaves and roots of the Ferns are large.
Natural selection reduces the size of a structure that is no longer good for it's environment.
There is a green stem of a whisk.
There are small yellow knobs at the tip of the branch.
A recent analysis of DNA suggests that the whisk ferns are related to the true ferns, and that they may have lost both vascular tissue and roots through evolution.
There are 12,000 species of ferns in the world.
Most ferns are restricted to moist and shaded areas.
The specimen can grow very tall.
The geological time scale begins with the Pre-Archean eon 3800 million years ago and ends with the Quaternary period in present time.
To see an animation of a fern's lifecycle, go to this.
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