Seedless Plants
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C ONCEPT
Concept 1. Seedless Plants
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Seedless Plants
Lesson Objectives
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I can name examples of nonvascular seedless plants.
I can name examples of vascular seedless plants.
I can explain the reproduction strategies of seedless plants.
I can describe the ways seedless plants impact humankind.
Check Your Understanding
• What is a plant?
• How are plants classified?
Vocabulary
club mosses
Seedless vascular plants that resemble mosses.
ferns
Seedless vascular plants that have large, divided fronds.
hornworts
Seedless nonvascular plants with hornlike sporophytes.
horsetails
Seedless vascular plants with hollow, rigid stems.
liverworts
Seedless nonvascular plants that can have flattened bodies resembling a liver.
mosses
Seedless nonvascular plants with tiny stem-like and stem-like structures.
sporangium
Capsule, formed by the sporophyte, which releases spores.
whisk ferns
Seedless nonvascular plants with tiny stem-like and stem-like structures.
Seedless Plants
What do you think a forest looked like millions of years ago? Or tens of millions of years ago? Or hundreds of
millions of years ago? Probably very different than today.
Nonvascular seedless plants and vascular seedless plants have had a great impact on all our lives. More than 300
million years ago, during the Carboniferous period, forests looked very different than they do today. Seedless plants
grew as tall as today’s trees in large swampy forests (Figure 1.1). The remains of these forests formed the coal that
we depend on today. Although most of these giant seedless plants are now extinct, smaller relatives still remain.
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FIGURE 1.1
Seedless plants were dominant during
the Carboniferous period, as illustrated by
this drawing.
Nonvascular Seedless Plants
Nonvascular seedless plants, as their name implies, lack vascular tissue. Of course, they don’t have seeds either.
As they lack vascular tissue, they also do not have true roots, stems or leaves. Nonvascular plants do often have a
“leafy” appearance though, and can have stem-like and root-like structures. These plants are very short because they
cannot move nutrients and water up a stem.
Nonvascular plants are classified into three phyla:
a. Mosses
b. Hornworts
c. Liverworts
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Concept 1. Seedless Plants
Mosses
Mosses have a scientific name, Bryophyta. They are most often recognized as the green “fuzz” on damp rocks and
trees in a forest. If you look closely, you will see that most mosses have tiny stem-like and leaf-like structures. This
is the gametophyte stage. Remember that a gametophyte is haploid. The gametophyte produces the gametes that,
after fertilization, develop into the diploid sporophyte. The sporophyte forms a capsule, called the sporangium,
which releases spores (Figure 1.2).
FIGURE 1.2
Sporophytes sprout up on stalks from this
bed of moss gametophytes. Notice that
both the sporophytes and gametophytes
exist at the same time.
Hornworts
Hornworts are part of the phylum Anthocerophyta. The "horn" part of the name comes from their hornlike
sporophytes, and “wort” comes from the Anglo-Saxon word for herb. The hornlike sporophytes grow from a base
of flattened lobes, which are the gametophytes (Figure 1.3). They usually grow in moist and humid areas.
Liverworts
Liverworts are in the phylum Hepatophyta. They have two distinct appearances: they can either be leafy like
mosses, or flattened and ribbon-like. Liverworts get their name from the type with the flattened bodies, which can
resemble a liver (Figure 1.4). Liverworts can often be found along stream beds.
Vascular Seedless Plants
For these plants, the name says it all. Vascular seedless plants have vascular tissue but do not have seeds. Remember
that vascular tissue is specialized tissue that transports water and nutrients throughout the plant. The development of
vascular tissue allowed these plants to grow much taller than nonvascular plants, forming the ancient swamp forests
mentioned previously. Most of these large vascular seedless plants are now extinct, but their smaller relatives still
remain.
Seedless vascular plants include:
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FIGURE 1.3
In hornworts, the “horns” are the sporophytes that rise up from the leaflike gametophyte.
FIGURE 1.4
Liverworts with a flattened, ribbon-like
body are called thallose liverworts.
a.
b.
c.
d.
Club mosses.
Ferns.
Horsetails.
Whisk ferns.
Clubmosses
Clubmosses, in the phylum Lycophyta, are so named because they can look similar to mosses (Figure 1.5). Clubmosses are not true mosses, though, because they have vascular tissue. The “club” part of the name comes from
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Concept 1. Seedless Plants
club-like clusters of sporangia found on the plants. One type of clubmoss is called the "resurrection plant" because
it shrivels and turns brown when it dries out, but then quickly turns green when watered again.
FIGURE 1.5
Clubmosses can resemble mosses, but
clubmosses have vascular tissue, while
mosses do not.
Ferns
Ferns, in the phylum Pterophyta, are the most common seedless vascular plants (Figure 1.6). They usually have
large divided leaves called fronds. In most ferns, fronds develop from a curled-up formation called a fiddlehead
(Figure 1.7). The fiddlehead looks like the curled decoration on the end of a stringed instrument, such as a fiddle.
Leaves unroll as the fiddleheads grow and expand. Ferns grow in a variety of habitats, ranging in size from tiny
aquatic species to giant tropical plants.
FIGURE 1.6
Ferns are common in the understory of the tropical rainforest.
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FIGURE 1.7
The first leaves of most ferns appear curled up into fiddleheads.
Horsetails
Horsetails, in the phylum Sphenophyta, have hollow, ribbed stems and are often found in marshes (Figure 1.8).
Whorls of tiny leaves around the stem make the plant look like a horse’s tail, but these soon fall off and leave a
hollow stem that can perform photosynthesis (mostly, photosynthesis occurs in leaves). The stems are rigid and
rough to the touch because they are coated with a scratchy mineral. Because of their scratchy texture, these plants
were once used as scouring pads for cleaning dishes.
FIGURE 1.8
Horsetails are common in marshes.
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Concept 1. Seedless Plants
Whisk Ferns
Whisk ferns, in the phylum Psilophyta, have green branching stems with no leaves, so they resemble a whisk broom
(Figure 1.9). Another striking feature of the whisk ferns is its spherical yellow sporangia.
FIGURE 1.9
Whisk ferns have no leaves and bear
yellow sporangia.
Reproduction of Seedless Plants
Seedless plants can reproduce asexually or sexually. Some seedless plants, like hornworts and liverworts, can
reproduce asexually through fragmentation. When a small fragment of the plant is broken off, it can form a new
plant.
Reproduction in Nonvascular Seedless Plants
Like all plants, nonvascular plants have an alternation of generations life cycle. In the life cycle of the nonvascular
seedless plants, the gametophyte stage is the longest part of the cycle. The gametophyte is photosynthetic.
The life cycle of nonvascular seedless plants can be described as follows:
a. The male gametophyte produces flagellated sperm that must swim to the egg formed by the female gametophyte. For this reason, sexual reproduction must happen in the presence of water. Therefore, nonvascular
plants tend to live in moist environments.
b. Following fertilization, the sporophyte forms. The sporophyte is connected to and dependent on the gametophyte.
c. The sporophyte produces spores that will develop into gametophytes and start the cycle over again.
Reproduction in Seedless Vascular Plants
For the seedless vascular plants, the sporophyte stage is the longest part of the cycle, but the cycle is similar to
nonvascular plants. For example, in ferns, the gametophyte is a tiny heart-shaped structure, while the leafy plant we
recognize as a fern is the sporophyte (see Figure 1.9).
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The sporangia of ferns are often on the underside of the fronds (Figure 1.10). Like nonvascular plants, ferns also
have flagellated sperm that must swim to the egg. Unlike nonvascular plants, once fertilization takes place, the
gametophyte will die and the sporophyte will live independently.
FIGURE 1.10
This fern is producing spores underneath
its fronds.
Why Seedless Plants Are Important
Seedless Plants Became Coal
The greatest influence of seedless plants have had on human society is in the formation of coal millions of years ago.
When the seedless plants died, became buried deep in the earth, and were exposed to heat and pressure, coal formed.
Now coal is burned to provide energy, such as electricity.
Current Uses
But some seedless plants still have uses in society today. Peat moss, is commonly used by gardeners to improve soils
since it is really good at absorbing and holding water (Figure 1.11).
Ferns are also found in many gardens as ornaments. The fiddleheads of certain species of ferns are used in gourmet
food. Some species of ferns, like the maidenhair fern, are used as medicines.
Lesson Summary
• Nonvascular seedless plants include mosses, liverworts, and hornworts.
• Vascular seedless plants include clubmosses, ferns, whisk ferns, and horsetails.
• Nonvascular seedless plants spend most of their life cycle in the gametophyte stage, while vascular seedless
plants spend most of their life as a sporophyte.
• The death of seedless plants millions of years ago produced coal.
• Mosses and ferns are used commonly in gardening.
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Concept 1. Seedless Plants
FIGURE 1.11
Sphagnum, or peat moss, is commonly
added to soil to help absorb water and
keep it in the soil.
Review Questions
Recall
1. What is vascular tissue?
2. What is an example of a nonvascular seedless plant?
3. What is an example of a vascular seedless plant?
4. Compare and contrast the fern gametophyte and sporophyte.
5. What are some of the distinguishing features of horsetails?
6. What does the sporophyte of the hornwort look like?
Apply Concepts
7. Your friend finds a whisk fern and insists it is the same as a fern. Explain why it is different.
8. Explain why the following quote is true: "Clubmoss is not a type of moss."
Critical Thinking
9. "After they died, many seedless plants have been a great benefit to humans." Explain why you agree or disagree
with the statement.
10. Explain to a group of gardeners how they may use seedless plants.
Further Reading / Supplemental Links
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http://www.cavehill.uwi.edu/FPAS/bcs/bl14apl/bryo1.htm
http://www.microscopy-uk.org.uk/mag/indexmag.html
http://www.microscopy-uk.org.uk/mag/artjul98/jpmoss.html
http://www.biologycorner.com/bio2/notes_plants.html
http://forestencyclopedia.com/p/p1893
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http://www.hiddenforest.co.nz/plants/clubmosses/clubmosses.htm
http://amerfernsoc.org/
http://www.washjeff.edu/greenhouse/Pnudum
http://en.wikipedia.org/wiki
Points to Consider
Next we discuss plants with seeds.
• Can you think of examples of plants that have seeds?
• Can you think of a plant that has seeds but no flowers or fruits?
• Why do you think having flowers is beneficial to a plant?
club mosses
Seedless vascular plants that resemble mosses.
ferns
Seedless vascular plants that have large, divided fronds.
hornworts
Seedless nonvascular plants with hornlike sporophytes.
horsetails
Seedless vascular plants with hollow, rigid stems.
liverworts
Seedless nonvascular plants that can have flattened bodies resembling a liver.
mosses
Seedless nonvascular plants with tiny stem-like and stem-like structures.
sporangium
Capsule, formed by the sporophyte, which releases spores.
whisk ferns
Seedless nonvascular plants with tiny stem-like and stem-like structures.
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