Download Biological Diversity 5

BIOLOGICAL DIVERSITY: NONVASCULAR PLANTS AND NONSEED VASCULAR
PLANTS
Table of Contents
Evolution of Plants | The Plant Life Cycle | Plant Adaptations to Life on Land
Bryophytes | Tracheophytes: The Vascular Plants | Vascular Plant Groups | The Psilophytes | The
Lycophytes
The Sphenophyta | The Ferns | Learning Objectives | Terms | Review Questions | Links
The plant kingdom contains multicellular phototrophs that usually live on land. The earliest
plant fossils are from terrestrial deposits, although some plants have since returned to the water.
All plant cells have a cell wall containing the carbohydrate cellulose, and often have plastids in
their cytoplasm. The plant life cycle has an alternation between haploid (gametophyte) and
diploid (sporophyte) generations. There are more than 300,000 living species of plants known,
as well as an extensive fossil record.
Plants divide into two groups: plants lacking lignin-impregnated conducting cells (the
nonvascular plants) and those containing lignin-impregnated conducting cells (the vascular
plants). Living groups of nonvascular plants include the bryophytes: liverworts, hornworts, and
mosses. Vascular plants are the more common plants like pines, ferns, corn, and oaks. The
phylogenetic relationships within the plant kingdom are shown in Figure 1.
Figure 1. Phylogenetic reconstruction of the possible relationships between plant groups and
their green algal ancestor. Note this drawing proposes a green algal group, the Charophytes, as
possible ancestors for the plants. Image from Purves et al., Life: The Science of Biology, 4th
Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com),
used with permission.
Evolution of Plants | Back to Top
Fossil and biochemical evidence indicates plants are descended from multicellular green algae.
Various green algal groups have been proposed for this ancestral type, with the Charophytes
often being prominently mentioned. Cladistic studies support the inclusion of the Charophytes
(including the taxonomic order Coleochaetales) as sister taxa to the land plants. Algae
dominated the oceans of the precambrian time over 700 million years ago. Between 500 and 400
million years ago, some algae made the transition to land, becoming plants by developing a
series of adaptations to help them survive out of the water.
Table 1. Photosynthetic pigments of algae and plants. Prokaryote groups are shown in red,
protists in blue, and vascular plants in purple.
Taxonomic
Group
Photosynthetic Pigments
chlorophyll a, chlorphyll c,
phycocyanin, phycoerythrin
Chloroxybacteria chlorophyll a, chlorphyll b
Cyanobacteria
Green Algae
(Chlorophyta)
Red Algae
(Rhodophyta)
Brown Algae
(Phaeophyta)
Golden-brown
Algae
(Chrysophyta)
chlorophyll a, chlorphyll b,
carotenoids
chlorophyll a, phycocyanin,
phycoerythrin, phycobilins
chlorophyll a, chlorphyll c,
fucoxanthin and other
carotenoids
chlorophyll a, chlorphyll c,
fucoxanthin and other
carotenoids
Dinoflagellates
(Pyrrhophyta)
Vascular Plants
chlorophyll a, chlorphyll c,
peridinin and other carotenoids
chlorophyll a, chlorphyll b,
carotenoids
Vascular plants appeared by 350 million years ago, with forests soon following by 300 million
years ago. Seed plants next evolved, with flowering plants appearing around 140 million years
ago. This pattern is shown in Figure 2.
Figure 2. The fossil records of some protist and plant groups. The width of the shaded space is
an indicator of the number of species. Image from Purves et al., Life: The Science of Biology,
4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
The Plant Life Cycle | Back to Top
Plants have an alternation of generations: the diploid spore-producing plant (sporophyte)
alternates with the haploid gamete-producing plant (gametophyte), as shown in Figure 3.
Animal life cycles have meiosis followed immediately by gametogenesis. Gametes are produced
directly by meiosis. Male gametes are sperm. Female gametes are eggs or ova.
Figure 3. Typical alternation of generations life cycle, such as occur in some protistans and
plants. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer
Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
The plant life cycle has mitosis occurring in spores, produced by meiosis, that germinate into
the gametophyte phase. Gametophyte size ranges from three cells (in pollen) to several million
(in a "lower plant" such as moss). Alternation of generations occurs in plants, where the
sporophyte phase is succeeded by the gametophyte phase. The sporophyte phase produces
spores by meiosis within a sporangium. The gametophyte phase produces gametes by mitosis
within an antheridium (producing sperm) and/or archegonium (producing eggs). These different
stages of the flowering plant life cycle are shown in Figure 4. Within the plant kingdom the
dominance of phases varies. Nonvascular plants, the mosses and liverworts, have the
gametophyte phase dominant. Vascular plants show a progression of increasing sporophyte
dominance from the ferns and "fern allies" to angiosperms.
Figure 4. The life cycle stages of a flowering plant. The above image is reduced from
gopher://wiscinfo.wisc.edu:2070/I9/.image/.bot/.130/Angiosperm/Angiosperm_life_cycle.
Follow that link to view a larger image.
Homospory and Heterospory
Plants have two further variations on their life cycles. Plants that produce bisexual gametophytes
have those gametophytes germinate from isospores (iso=same) that are about all the same size.
This state is referred to as homospory (sometimes referred to as isospory). A generalized
homosporous plant life cycle is shown in Figure 5. Homosporous plants produce bisexual
gametophytes. Ferns are a classic example of a homosporous plant.
Figure 5. A typical homosporous life cycle. Note the production of a single type of bisexual
gametophyte that will eventually produce the antheridia (sperm bearing structures) and
archegonia (egg bearing structures). Image from Purves et al., Life: The Science of Biology,
4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
Plants that produce separate male and female gametophytes have those gametophytes germinate
from (or within in the case of the more advanced plants) spores of different sizes (heterospores;
hetero=different). The male gametophyte produces sperm, and is associated with smaller or
microspores. The female gametophyte is associated with the larger or megaspores. Heterospory
is considered by botanists as a significant step toward the development of the seed. A
generalized heterosporous life cycle is shown in Figure 6.
Figure 6. Typical heterosporous life cycle. Note the production of separate, unisexual male and
female gametophytes. Image from Purves et al., Life: The Science of Biology, 4th Edition, by
Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
Plant Adaptations to Life on Land | Back to Top
Organisms in water do not face many of the challenges that terrestrial creatures do. Water
supports the organism, the moist surface of the creature is a superb surface for gas exchange,
etc. For organisms to exist on land, a variety of challenges must be met.
1. Drying out. Once removed from water and exposed to air, organisms must deal with the
need to conserve water. A number of approaches have developed, such as the development
of waterproof skin (in animals), living in very moist environments (amphibians,
bryophytes), and production of a waterproof surface (the cuticle in plants, cork layers and
bark in woody trees).
2. Gas exchange. Organisms that live in water are often able to exchange carbon dioxide and
oxygen gases through their surfaces. These exchange surfaces are moist, thin layers across
which diffusion can occur. Organismal response to the challenge of drying out tends to
make these surfaces thicker, waterproof, and to retard gas exchange. Consequently,
another method of gas exchange must be modified or developed. Many fish already had
gills and swim bladders, so when some of them began moving between ponds, the swim
bladder (a gas retention structure helping buoyancy in the fish) began to act as a gas
exchange surface, ultimately evolving into the terrestrial lung. Many arthropods had gills
or other internal respiratory surfaces that were modified to facilitate gas exchange on land.
Plants are thought to share common ancestry with algae. The plant solution to gas
exchange is a new structure, the guard cells that flank openings (stomata) in the above
ground parts of the plant. By opening these guard cells the plant is able to allow gas
exchange by diffusion through the open stomata.
3. Support. Organisms living in water are supported by the dense liquid they live in. Once on
land, the organisms had to deal with the less dense air, which could not support their
weight. Adaptations to this include animal skeletons and specialized plant cells/tissues that
support the plant.
4. Conduction. Single celled organisms only have tyo move materials in, out, and within
their cells. A multicellular creature must do this at each cell in the body, plus move
material in, out, and within the organism. Adaptations to this include the circulatory
systems of animals, and the specialized conducting tissues xylem and phloem in plants.
Some multicellular algae and bryophytes also have specialized conducting cells.
5. Reproduction. Organisms in water can release their gametes into the water, where the
gametes will swim by flagella until they ecounter each other and fertilization happens. On
land, such a scenario is not possible. Land animals have had to develop specialized
reproductive systems involving fertilization when they return to water (amphibians), or
internal fertilization and an amniotic egg (reptiles, birds, and mammals). Insects developed
similar mechanisms. Plants have also had to deal with this, either by living in moist
environments like the ferns and bryophytes do, or by developing specialized delivery
systems like pollen tubes to get the sperm cells to the egg.
Bryophytes | Back to Top
Bryophytes are small, nonvascular plants that first evolved approximately 500 million years ago.
The earliest land plants were most likely bryophytes. Bryophytes lack vascular tissue and have
life cycles dominated by the gametophyte phase, as shown in Figure 7. The lack of conducting
cells limits the size of the plants, generally keeping them under 5 inches high. Roots are absent
in bryophytes, instead there are root-like structures known as rhizoids. Bryophytes include the
hornworts, liverworts, and mosses.
Figure 7. The moss life cycle. The haploid gametophyte phase is free-living and
photosynthetic. The diploid sporophyte grows from and is nourished by the gametophyte.
Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
(www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
Tracheophytes: The Vascular Plants | Back to Top
The vascular plants have specialized transporting cells xylem (for transporting water and mineral
nutrients) and phloem (for transporting sugars from leaves to the rest of the plant). When we
think of plants we invariably picture vascular plants. Vascular plants tend to be larger and more
complex than bryophytes, and have a life cycle where the sporophyte is more prominent than the
gametophyte. Vascular plants also demonstrate increased levels of organization by having
organs and organ systems. The novel features oif the vascular plants are summarized in Table 2.
Table 2. Major evolutionary advances of the vascular plants.
Advance
Green Algae
Bryophytes
nonvascularized body
Development
(thallus) that may be no vascular system
of the rootvariously shaped
stem-leaf
leaflike structures are present,
vascular
no levaes, shoots, or but lack any vascular tissue
system
roots
Reduction in
the size of
the
gametophyte
generation
Development
of seeds in
wide range of life
cycles, some
gametophyte
dominant, others
sporophyte dominant
Tracheophytes
early vascular plants are naked,
rootless vascularized stems
later vascular plants develop
vascularized leaves, then roots
progressive reduction in size and
complexity of the gametoiphyte
generation, leading to its complete
dependance on the sporophyte for
food
sporophyte generation
dependant on gametophyte
generation for food;
gametophyte is free-living and
in angiosperms, 3 celled male
photosynthetic
gametophyte and a (usually) 8 celled
female gametophyte
of seeds in
some
vascular
plants
no seeds
spores for resisting
Spores/Pollen environmental
degradation
no seeds
seed plants retain the female
gametophyte on the sporophyte
Spores that germinate into the
Spores that germinate into the gametophyte generation or spores
gametophyte generation
that have the gametophyte generation
develop within themselves
Vascular Plant Groups | Back to Top
Vascular plants first developed during the Silurian Period, about 400 million years ago. The
earliest vascular plants had no roots, leaves, fruits, or flowers, and reproduced by producing
spores.
Cooksonia, shown in Figure 8, is a typical early vascular plant. It was less than 15 cm tall, with
stems that dichotomously branched. Dichotomous branching (where the stem divides into two
ewqual branches) appears a primitive or ancestral trait in vascular plants. Some branches
terminated in sporangia that produced a single size of spore.
Many scientists now consider "Cooksonia" an evolutionary grade rather than a true
monophyletic taxon. Their main argument is that not all stems of Cooksonia-type plants have
vascular tissue. The evolutionary situation of a grade would have some members of the group
having the trait, others not. The shapes of sporangia on various specimens of Cooksonia also
vary considerably.
Figure 8. Cooksonia fossil specimen (L) and reconstruction (R). Both Images from
http://www.ucmp.berkeley.edu.
Rhynia, shown in Figure 9, is another early vascular plant. Like Cooksonia, it lacked leaves and
roots. One of the species formerly assigned to this genus, R. major, has since been reclassified
as Aglaophyton major. Some paleobotanists consider A. major (Figure 10) a bryophyte,
however, it does have a separate free-living sporophyte that is more prominent than the
sporophyte, but appears to lack lignified conducting cells. The remaining species, R. gwynnevaughanii is an undoubted vascular plant.
Figure 9. Rhynia gwynne-vaughanii (L) stem cross section from the Rhynie Chert in Scotland.
Image cropped and reduced from http://www.unimuenster.de/GeoPalaeontologie/Palaeo/Palbot/rhynie.html. (R) Reconstruction of the plant,
from http://www.ucmp.berkeley.edu/IB181/VPL/Elp/Elp2.html.
Figure 10. Reconstruction of Aglaophyton major (A-C) and Lyonophyton rhyniensis, another
Rhynie Chert plant thought to be the gametophyte of Aglaophyton. Image from the UCMP
Berkeley website.
Devonian plant lines included the trimerophytes and zosterophyllophytes, which have been
interpreted as related to ferns and lycophytes.
The Psilophytes | Back to Top
The Division Psilophyta consists of Psilotum nudum (the whisk fern, shown in Figure 11), a
living plant that resembling what paleobotanists believe Cooksonia to have been: a naked,
photosynthetic stem bearing sporangia. Also in the group is Tmesipteris, which resembles
Psilotum except for its possession of smallo vascularized leaves arising on opposite sides of the
stem. However, most paleobotanists doubt that Psilotum is a direct descendant of Cooksonia.
Molecular studies suggest an affiliation with ferns for Psilotum. Psilotum also has three fused
sporangia, termed a synangium, located on the sides of the stems (instead of the tips of stems as
in Cooksonia).
Figure 11. Psilotum nudum from Hawaii. Note the synangia, the roundish structures on the side
of the green stems. Image from
http://www.botany.hawaii.edu/faculty/carr/images/psi_nud_mid.jpg.
The Lycophytes | Back to Top
The next group, the Division Lycophyta, have their sporangia organized into strobili (singular:
strobilus). A strobilus is a series of sporangia and modified leaves closely grouped on a stem tip.
The leaves in strobili are soft and fleshy as opposed to the hard, modified leaves in cones.
Leaves that contained vascular tissue are another major advance for this group. The presumed
evolutionary pathway for the leaf is shown in Figure 12. The leaves in lycophytes, both living
and fossil forms, are known as microphylls. This term does not imply any size constraint, but
rather refers to the absence of a leaf gap in the vascular supply of the stem at the point where
the leaf vascular trace departs. Ferns and other plants have megaphylls, leaves that produce this
leaf gap.
Figure 12. Proposed steps in the evolution of the microphyll leaf. Note that microphylls do not
leave a leaf gap in the stem's vascular cylinder. If we wanted to place Psilotum-like plants on
the left top, we would have Lycopodium-like plants on the right top. Image from Purves et al.,
Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH
Freeman (www.whfreeman.com), used with permission.
Today there are fewer genera of lycophytes than during the group's heyday, the Paleozoic Era.
Major living lycophytes include Lycopodium (commonly called the club moss [shown in Figure
13], although it is NOT a moss), Isoetes, and Selaginella (the so-called resurrection plant).
Lycopodium produces isospores that germinate in the soil and produce a bisexual gametophyte.
These spores are all approximately the same size. Selaginella and Isoetes are heterosporous, and
thus produce two sizes of spores: small spores (termed microspores) that germinate to produce
the male gametophyte; and larger spores (megaspores) that germinate to produce the female
gametophyte. The production of two sizes of spores, and also making separate unisexual
gametophytes, is thought an important step toward the seed. Modern lycophytes are small,
herbaceous plants. Many of the prominent fossil members of this group produced large amounts
of wood and were significant trees in the Carboniferous-aged coal swamps.
Figure 13. Lycopodium venustulum, from from Hawaii. Note the strobili on the tips of the
stems, as well as the stems covered with numerous spirally arranged microphylls. Image from
http://www.botany.hawaii.edu/faculty/carr/images/lyc_ven.jpg.
Selaginella is a heterosporous member of the lycophytes. Some species of this genus are able to
withstand drying out by going dormant until they are rehydrated. For this reason these forms of
the genus are commonly called resurrection plants. An example of this is shown in Figure 14.
Figure 14. Selaginella lepidophylla. The top part of the image shows the dried plant, the middle
part shows the resurrected or rehydrated plant. Image from
http://www.orchideeitalia.it/selaginella.jpg.
Fossil Lycophytes: Baragwanathia and Drepanophycus
Baragwanathia, shown in Figure 15, is an undoubted lycophyte from the middle Silurian
deposits of Australia. It has microphyllous leaves spirally attached to the stem, and sporangia
clustered in some areas of the plant, although not in terminal strobili as in modern lycophytes.
Figure 15. Left: Reconstruction of Baragwanathia longifolia, from the middle Silurian of
Australia. Image from http://www.ucmp.berkeley.edu/IB181/VPL/Lyco/Lyco1.html; Right:
Reconstruction of Drepanophycus , a middle Devonian lycophyte. Note the numerous
microphyll leaves, placement of sporangia on the upper surface of the sporophylls, and stem
anatomy that are all consistent with modern lycophytes. Image from
http://www.ucmp.berkeley.edu/IB181/VPL/Lyco/Lyco2.html.
Drepanophycus is a middle Devonian lycophyte from the Northern Hemisphere, also shown in
Figure 15. Its features are very similar to modern lycophytes.
Lepidodendron and Sigillaria
The Lycophytes became significant elements of the world's flora during the Carboniferous time
(the Mississippian and Pennsylvanian are terms used for this time span in the United States).
These non-seed plants evolved into trees placed in the fossil genera Lepidodendron and
Sigillaria, with heights reaching up to 40 meters and 20-30 meters respectively. Lepidodendron
stems are composed of less wood (secondary xylem) that usually is found in gymnosperm and
angiosperm trees.
We know much about the anatomy of these coal-age lycopods because of an odd type of
preservation known as a coal ball. Coal balls can be peeled and the plants that are anatomically
preserved within them laboriously studied to learn the details of cell structure of these coal age
plants. Additionally, we have some exceptional petrifactions and compressions that reveal
different layers of the plants' structure. Estimates place the bulk, up to 70%, of coal material as
being derived from lycophytes.
Lepidodendron, pictured in Figures 16 and 17, was a heterosporous lycophyte tree common in
coal swamps of the Carboniferous time. As with many large plant fossils, one rarely if ever
finds the entire tree preserved intact. Consequently there are a number of fossil plant genera that
are "organ taxa" and represent only the leaves (such as Lepidophylloides), reproductive
structures (Lepidostrobus), stem (Lepidodendron), spores (Lycospora), and roots (Stigmaria).
Lepidodendron had leaves borne spirally on branches that dichotomously forked, with roots also
arising spirally from the stigmarian axes, and both small (microspores) and large (megaspores)
formed in strobili (a loose type of soft cone). Lepidodendron may have attained heigths of
nearly 40 meters, with trunks nearly 2 meters in diameter. The trees branched extensively and
produced a large number of leaves. When these leaves fell from the branches, they left behind
them the leaf scars characteristic of the genus.
Figure 16. External stem features typical of arborescent lycopods, collectively called
lepidodendrids, based on the diamond-shaped "snakeskin" type pattern produced by the
helically arranged leaf cushions. On the left is a lower magnification view of this type of
pattern, showing the general features of many of these trees. Each leaf abscissed, so that if you
are looking, as you are here, at the outside of the stem, you can see a characteristic appearance.
On the right is a higher magnification photo showing details of leaf cushions. Each diamond
shaped cushion has a smaller central area called the leaf base where the leaf attached. In the
center of the leaf base you can see the leaf trace, or vein to the leaf. The vertical stripe running
down each cushion is probably the result of increased girth from secondary cortical growth
inside the stem. Images and text from http://lsvl.la.asu.edu/plb407/kpigg/lepidodendrid.htm,
used with permission of K.B. Pigg, Arizona State University.
Figure 17. Top: Cross section through a branch (approximately an inch in diameter) of a large
lepidodendrid tree. In the very center is a pith, surrounded by primary xylem and a small fringe
of secondary xylem [wood, MJF]. Then there is black gunk and an open white area. Phloem
and innermost cortical tissues are typically not well preserved, and this black gunk and white
areas probably represent their positions in the branch. The outermost part of the stem is gone.
Images and text from http://lsvl.la.asu.edu/plb407/kpigg/lepidostemxs.htm, used with
permission of K.B. Pigg, Arizona State University. Bottom: Reconstructed diorama of
Carboniferous forest scene. Note the ferns and sphenopsids growing around the fallen
Lepidodendron trunk, and a large calamite tree in the right foreground. Image and text from
http://seaborg.nmu.edu/earth/carbonif/car01b.html.
Sigillaria was another arborescent lycopod, and is also common in coal-age deposits. In contrast
to the spirally borne leaves of Lepidodendron, Sigillaria had leaved arranged in vertical rows
along the stem.
The Sphenophyta | Back to Top
The Division Sphenophyta contains once dominant plants (both arborescent as well as
herbaceous) in Paleozoic forests, equisetophytes are today relegated to minor roles as
herbaceous plants. Today only a single genus, Equisetum, survives. The group is defined by
their jointed stems, with many leaves being produced at a node, production of isospores in cones
borne at the tips of stems, and spores bearing elaters (devices to aid in spore dispersal).
Sporophyte features are seen in Figure 18. The gametophyte is small, bisexual, photosynthetic,
and free-living. Silica concentrated in the stems give this group one of their common names:
scouring rushes. These plants were reportedly used by American pioneers to scour the pots and
pans. The fossil members of this group are often encountered in coal deposits of Carboniferous
age in North America and Europe.
Figure 18. Top: A branched species of Equisetum from Hawaii. Note that the branches arise
from the same node/area along the stem. Image from
http://www.botany.hawaii.edu/faculty/carr/images/equ_sp.jpg. Bottom: Closeup view of the
cone of Equisetum hyemale from Hawaii. Note the small leaves at the joints near the lettering
in the picture. Image from http://www.botany.hawaii.edu/faculty/carr/images/equ_sp_cu.jpg.
The Ferns | Back to Top
Ferns reproduce by spores from which the free-living bisexual gametophyte generation
develops. There are 12,000 species of ferns today, placed in the Division Pteridophyta. The
fossil history of ferns shows them to have been a dominant plant group during the Paleozoic
Era. Most ferns have pinnate leaves, exhibiting small leaflets on a frond, as shown in Figure 19.
Ferns have megaphyllous leaves, which cause a leaf gap in the vascular cylinder of the
stem/rhizome, as shown in Figure 20. The first ferns also appear by the end of the Devonian.
Some anatomical similarities suggest that ferns and sphenophytes may have shared a common
ancestor within the trimerophytes.
Figure 19. Three genera of the fern family Gleicheniaceae from Hawaii: Upper left: Sticheris
owhyhensis, lower left: Diploterygium pinnatum (uluhe lau nui), right: Dicranopteris linearis
(uluhe). Image from http://www.botany.hawaii.edu/faculty/carr/gleicheni.htm.
Figure 20. Formation of leaf gaps by a megaphyllous leaf. Most plants above the ferns have
megaphyllous leaves. Image from Purves et al., Life: The Science of Biology, 4th Edition, by
Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
The Fern Life Cycle
The fern gametophyte has both sexes present and is referred to as a prothallium. Prothallia
develop from spores shed from the underside of the sporophyte leaves, shown in Figure 21.
Once fertilization occurs, the next generation sporophyte develops from the egg located in the
prothallium.
Figure 21. Sporangia on the underside of Polypodium pellucidum from Hawaii. Image from
http://www.botany.hawaii.edu/faculty/carr/images/pol_pel.jpg.
Composite of 4 segmented diagrams of the fern life cycle. Note: to view this in its proper
sequence you will need to open your browsert window as wide as possible. Images from Purves
et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and
WH Freeman (www.whfreeman.com), used with permission.
Learning Objectives | Back to Top
Be able to discuss the differences in life cycle between vascular and nonvascular plants.
Both bryophytes and vascular plants have leaf-like structures. Be able to prepare a single sentence that
can tell the reader what a leaf is, as well as what it is not.
Both heterospory and homospory impose certain constraints on the gametophyte generation. List some
of these.
Be able to compare and contrast the typical plant life cycle and a typical animal one.
Psilotum is NOT a primitive vascular plant, but rather has more genetic similarity to ferns. What sorts
of information might we gather from studying modern Psilotum and its ecology as it relates to
Cooksonia and other early vascular plants.
What are the chief differences between vascular and nonvascular plants?
The fern gametophyte is bisexual. Speculate on the evolutionary advantages of this in fern
colonization of ecologically disturbed areas.
Terms | Back to Top
alternation of
generations
bark
bryophytes
homospory and
heterospory
nonvascular plants phototrophs pollen
gametophyte
sporophyte
guard cells
stomata
strobilus
Charophytes cork
cuticle
isospores
megaspores
microspores
rhizoids
vascular
plants
spores
xylem and
phloem
sporangium
Review Questions | Back to Top
1. Which of these plant groups may include the ancestors of plants? a) red algae; b) green algae; c)
brown algae; d) fungi ANS is b
2. Plants and their ancestral group share which of the following features? a) chlorphylls a and b; b)
strach as a storage product; c) cellulose cell walls; d) all of these ANS is d
3. Vascular plants have ___, specialized cells that help support the plant as well as transport water and
nutrients upward from their roots. a) phloem; b) trumpet hyphae; c) xylem; d ) arteries ANS is c
4. The ___ generation of a moss is the dominant phase of its life history. a) sporophyte; b) adult; c)
embryo; d) gametophyte ANS is d
5. The lack of conducting cells in bryophytes limits their maximum size to ___. a) 100 meters; b) 5 cm;
c) 1 meter; d) no limit is set by the lack of these cells ANS is b
6. Which of these plants is known only from fossils? a) Cooksonia; b) Lycopodium; c) Equisetum; d)
Tmesipteris ANS is a
7. The ___ generation of a fern is the dominant phase of its life history. a) sporophyte; b) adult; c)
embryo; d) gametophyte ANS is a
Links | Back to Top
The Five Kingdoms A table summarizing the kingdoms of living things.
Green Plants from the Tree of Life pages at the University of Arizona. This series of pages leads you
deeper into the systematics of the plants and thier sister taxa.
Land Plants Online You can learn more about the various plant groups from this well organized site.
Follow links to look up the structure and geologic history of any major plant group of your choice.
Non-Flowering Plant Family Access Page Sorted by family on the non-flowering plants. Thumbnail
photos are linked to larger versions. This site is a great educational resource maintained by Gerald D.
Carr.
Introduction to the Bryophyta: The Mosses This University of California Museum of Paleontology site
offers a systematic perspective to the mosses by providing succinct information as well as links to a
number of pertinent sites.
Introduction to the Anthocerotophyta: The hornworts This University of California Museum of
Paleontology site offers a systematic perspective to the hornworts by providing succinct information
as well as links to a number of pertinent sites.
Encyclopedia of Plants Scientific and common names for garden plants, from a commercial site,
botany.com.
Garden Web Glossary A nice contrast to the above site, this glossary has over 4000 terms, and is also
from a commercial site.
Introduction to the Lycophyta: Club mosses and Scale trees This University of California Museum of
Paleontology site offers a systematic perspective to the lycophytes, their ecology, systematics, and
fossil record.
Introduction to the Sphenophyta: Yesterday's trees, today's horsetails This University of California
Museum of Paleontology site offers a systematic perspective to the sphenophytes (Equisetum and its
extinct relatives), their ecology, systematics, and fossil record.
Mazon Creek Fossils The Illinois State Museum maintains this site that details and illustrates some of
the exquisite plant and animal fossils from the Mazon Creek deposits in that state.
Plant Fossil Record An exhaustive resource for plant fossils maintained by the Organisation of
Palaeobotany.
Die Rhynie Chert Flora This site, in German, offers pictures illustrating the vascular nature, trilete
spores, and stomata that characterize Rhynia as a vascular plant. The site is also available in English.
Rhynie Chert, Scotland From the folks at the University of California Museum of Paleontology, this
site offers a closer look at the Rhynie Chert in Scotland, a significant fossil site with undisputed
vascular plant fossils.
The Botanical Society of America The official website of the plant biologists, oh well, call them
botanists!
Botany Online, The Internet Hypertextbook A wonderful, and still growing, site that offers a wealth of
details beyond what I have presented in my pages. Worth a look for those extra facts that make one
comfortable when discussing plants.
All text contents ©1995, 1999, 2000, 2001, 2003, 2004, by M.J. Farabee. Use of the text for educational
purposes is encouraged.
Back to Table of Contents
Email: [email protected]
Last modified:
The URL of this page is: