Plant Diversity
Laboratory Manual
Asst. Prof. Dr. İsmail EKER
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CHAPTER I. ALGAE
Algae are not classified into kingdom plantae and are found two different kingdoms.
Prokaryotic ones (Cyanobacteria) are placed in the kingdom Monera while eucaryotics
are found in the kingdom Protista
They are mostly photosynthetic
They range from unicellular species to multicellular ones
Unlike plants they do not have a cuticle and they do not have multicellular gametangia
(reproductive organs).
They all contain chlorophyll a and yellow and orange carotenoids. Classification of
different groups of algae is based on the presence of other types of photosynthetic
pigments.
Algae are important as primary producers of organic matter at the base of the food
chain.
Kingdom Monera
Division: Cyanobacteria (Blue-green algae)
• Photosynthetic prokaryotes, lacking nucleus membrane and the other membranous
organelles, such as chloroplast.
• Cyanobacteria are generally aquatic and can be unicellular, colonial or filamentous
• e.g. Nostoc, Oscillatoria, Spirulina, Anabaena, Chrococcus, Gleocapsa, Microcystis
Kingdom Protista
Division: Dinophyta = Pyrrhophyta (Dinoflagellates)
• About 2100 species
• Most are unicellular but some form colonies
• Their cells are covered by interlocking cellulose plates, and contain 2 grooves,
each with its own flagellum
• Most are photosynthetic (chlorophyll a and c, carotenoids, and fucoxanthin
(yellow-brown pigment)
• Some are endosymbiotic in jellyfish, corals and mollusks and are called
zooxanthellae. They provide host with photosynthetic carbohydrates.
• Some free-living forms cause red tides – dinoflagellate blooms in ocean waters.
They release a poison that is toxic to both fish and humans.
• e.g. Ceratium, Gonyaulax (red tide)
Division: Bacillariophyta (Diatoms)
• More than 5600 living diatoms are recognized, with almost as many more known only
as fossils; most are unicellular
• Most are photosynthetic (chlorophyll a and c, carotenoids, and fucoxanthin
(yellow-brown pigment). They do not have flagella.
• Have shells that are composed of 2 halves; one fitting into the other.; they are either
radially or bilaterally symmetrical. Shells contain silica, or glass like material in it.
• When they die, their shells do not decompose, but rather fall down to ocean sediments
to later become sedimentary rocks. Geologic upheavals can later expose these rocks
as diatomaceous earth (a white rock that is used in filtering and abrasives).
• e.g. Achnanthes, Cyclotella, Stephanodiscus,Cymbella,Diatoma, Fragilaria, Navicula,
Nitschia, Pinnularia, Surirella, Synedra, Tabellaria
Division: Chrysophyta (Golden Algae)
• Chrysophytes, or golden algae, are common microscopic
chromists in fresh water. Some species are colorless, but the
vast majority are photosynthetic. As such, they are particularly
important in lakes, where they may be the primary source of
food for zooplankton. They are not considered truly
autotrophic by some biologists because nearly all chrysophytes
become facultatively heterotrophic in the absence of adequate
light, or in the presence of plentiful dissolved food. When this
occurs, the chrysoplast atrophies and the alga may turn
predator, feeding on bacteria or diatoms.
• Contain chlorophyll a and c, and carotenoids, which are masked by the accessory
pigment fucoxanthin.
• e.g. Dinobryon, Synura
Division: Xanthophyta (Yellow Algae=Yellow-green Algae)
• Include more than 600 species.
• Photosynthetic organisms which live primarily in freshwater, though some are found
in marine waters, in damp soil, or on tree trunks.
• Completely lack the brown pigment fucoxanthin. Contain chlorophyll a and c, and
carotenoids.
• e.g. Vaucheria, Botrydium
Division: Charophyta (stoneworts)
• These are the 'stoneworts' - a type of green alga that grows with little
plant-like filamentous stems which have whorls of short branches
appearing at intervals. They grow in fresh or brackish water.
• the most closely related group of organisms to the Plantae
• show apical growth and are differentiated into nodal and internodal
regions
• Contain chlorophyll a and b, and carotenoids
• e.g. Chara
Division: Euglenophyta (Euglenoids)
• About 1000 species
• Most are unicellular flagellates (contain 2 flagella). They can change shapes because
their outer covering (the pellicle) is flexible rather than rigid
• Most are photosynthetic with chlorophyll a and b, and carotenoids. Like plants.
However they are not considered to be closely related to plants and green algae.
• They are also heterotrophs because they ingest other protists and bacteria.
• They have an eyespot, an orange or redish spot near the base of their flagellum that
they use to help orient them to the light.
• The reproduce asexually.
• e.g. Euglena,Trypanasoma
Division: Rhodophyta (Red Algae)
• There are about 4000 species; most are multicellular.
• In addition to chlorophyll a and carotenoids, they also contain phycoerythrin (a red
pigment).
•
Their cell walls contain polysaccharides that are important commercially. Both agar
and carrageenan are extracted from them. Both are thickening agents.
• Red algae carry out a complex form of sexual reproduction in which there is an
alternation of generations
• They live primarily in warm ocean waters
• e.g. Corallina, Polysiphonia, Batrachospermum
Division: Phaeophyta (Brown Algae)
• About 1500 species, all of which are multicellular
• Range in size from several cm to about 60 m (giant kelps of California). Bodies are
differentiated into blades (leaf like tissues), stipes (stems), and holdfasts (root like
structures). These structures are not homologous to the similar structures on plants
• They have chlorophyll a and c, carotenoids, and the yellow-brown pigment
fucoxanthin.
• Commercially brown algae are used as a source of algin, a thickening agent used in
various products.
• Reproduction is also complex with alternation of germinations.
• Common in cooler marine waters and especially in rocky intertidal areas.
• e.g. Dictyota, Cytoseira, Laminaria, Ectocarpus, Padina, giant kelp Nereocystis and
Macrocystis, gulf weed Sargassum (alginates to thicken ice cream)
Division: Green Algae (Chlorophyta)
• About 7000 species, across which there is a huge variety in form.
• Exhibit many different body forms and methods of reproduction
• Body forms include unicellular, colonial, multicellular, and coenocytic.
• They contain chlorophyll a and b, and carotenoids. They store excess food as
starch, and have cell walls composed of starch.
• Reproduction includes asexual, sexual, conjugation.
o Asexual: many form reproductive cells called spores by mitosis (zoospores if
they have flagella). Each spore can give rise to a new individual.
o Sexual: Involves the formation of gametes in unicellular gametangia. Three types
of sexual reproduction are recognized, all of which are based on the relative size of
the female and male gametes: isogamous, anisogamous, and oogamous
o Conjugation: Some species align up with each other and exchange genetic
material with each other (that is the DNA from one goes into the other cell).
• Green algae are very important ecologically because they form the base of the food
chain in many fresh water aquatic environments.
• e.g. Acetabularia, Chlorella (Chlorellin antibiotic), Chlorococcum, Cladophora,
Enteromorpha, Oedogonium, Oocystis, Ulva, Volvox, Gonium, Pandorina, Eudorina,
Zygnema, Ulothrix, Closterium, Scenedesmus, Pediastrum
* Experiment Procedures
a) for microscopic samples
- Take a drop of the sample water with a dropper
- Add it on the slide and place the coverslip
- Observe it under 10X and 40X magnifications
- Draw your observations under 40X magnification
- Try to determine names of division and/or genus according to algae atlas
b) for macroscopic samples
- Draw your observations with the naked eye and write the names of division and/or genus
CHAPTER II. SLIME MOLDS, TRUE FUNGI AND LICHENS
A. Slime Molds
Slime molds; - lack a cell wall
- move about like an amoeba
- resemble some protozoa
- produce walled spores during reproduction
Two distict divivisions of slime molds are known. In the acellular slime molds, the
cells agregate to produce a plasmodium, which is a multinucleate. Cellular slime molds
contain cellulose, whereas cellulose is lacking in the plasmodial slime molds.
1. Asrasiomycota (Cellular slime molds): They live in soil as independent haploid cells that
move and feed by producing extentions
Single, amoeba-like cells
emerge from spores,
crawl, and feed.
called pseudopods. These extensions
surround and engulf food such as
bacteria.
The best-studied
genus
is
Dictyostelium (Figure 1).
Pseudoplasmodium
migrates toward light,
forms fruting body in
which spores are
produced
When food becomes scarce, cells
aggregate into a sluglike mass
called a pseudoplasmodium
Figure 1. The life cycle of a cellular slime mold
2. Myxomycota (Acellular = Plasmodial slime molds): They consist of
a mass of
cytoplasm that may spread thinly over an
area of several square meters. Although the
mass contains thousand of diploid nuclei, the
nuclei are not confined in seperate cells
surrounded by plasma membranes,
Figure 2. The acellular slime mold Physarum
(Physarum oozes over a stone on the damp forest
floor)
as in most multicellular organisms. This structure, called a plasmodium, explains why these
protists are described as “acellular”. The plasmodium oozes through decaying and rotting
logs, engulfing food such as bacteria and particles of organic material (Figure 2). Dry
conditions or starvation stimulate the plasmodium to form a fruting body, on which haploid
spores are produced. The spores germinate under favorable conditions and give a new
plasmodium. The mass may be bright yellow or orange. The best-known genus is Physarum.
B. True Molds (=True Fungi=Eumycota)
All true fungi, except some unicellular yeasts, consists of long, branched filaments of
cells called hyphae. Hyphae form a mass of strands called a mycelium. Some hyphae have
no cell wall (nonseptate), while others contain septa (walls that divide the hyphae into
individual cells with one or more nuclei; oftentimes these walls have huge pores in them
allowing cytoplasm and nuclei to pass through) (Figure 3).
Fungi are eukaryote heterotrophs and their cell walls are made of chitin. They secrete
digestive enzymes onto living or dead organic material and then absorb small organic
molecules of the predigested food through their cell walls and membranes. Thus specifically
they are saprotrophs, while some are parasites. They can grow in a wide range of
environments
Figure 3. The flementous body of a fungus ( a. A fungal mycelium spreads over decaying vegetation. The
mycelium composed of b. a tangle of microscopic hyphae, only one cell thick, portreyed in cross section c. to
show their internal organization.
There are approximately 60.000 species of fungi. True fungi are seperated into six
main divisions. These divisions; Oomycota, Chytridiomycota, Zygomycota, Ascomycota,
Basidiomycota and Deuteromycota. Oomycota and Chytridiomycota are aquatic molds.
Zygomycota are terrestrial. These three divisions of true fungi are primitive members of
fungal kingdom (Lower fungi). They have a multinucleate, nonseptate, or rarely a septate
thallus.
Zygomycota (zygomycetes) – the bread molds
•
About 765 species of bread molds; they are typically the molds that you see develop
on foods in your refrigerator.
•
Asexual reproduction: the hyphae produce fruiting bodies called sporangia (spore
sacs). Each one through mitosis produces asexual spores (Figure 4).
•
Sexual reproduction: Occurs when hyphae of different mating types come together.
They grow together, produce a gametangium each which later fuse to make a diploid
nucleus. This new cell will then become zygospore which can wait out harsh
conditions. Just before germinating the diploid zygospore will undergo meiosis and
then produce a sporangium. The sporangium will then produce spores via mitosis.
Note that the zygospore is the only diploid structure in zygomycota (Figure 4).
Figure 4. The life cycle of zygomycotes
Ascomycota and Basidiomycota are higher fungi and have a septate thallus (Figure 3).
Ascomycota (ascomycetes) – the sac fungi
•
About 30.000 species. Called sac fungi because their sexual spores are produced in
little sacs called asci.
•
These include yeasts, powdery mildews, and most of the blue-green, pink, and brown
molds that cause food to spoil. Some cause serious plant diseases (e.g., Dutch-elm
disease).
•
Asexual reproduction: specialized hyphae known as conidiophores are produced. At
their tips conidia (spores) are produced by a pinching off process of the ends of the
hyphae.
•
Sexual reproduction: opposite mating types come together and fuse. A new
dikaryotic hyphal network is produced. These will later produce a fruiting body called
ascocarp. On the ascocarp in specialized cells called asci, the 2 nuclei fuse. Then
through meiosis, haploid spores are produced (called ascospores) (Figure 5).
•
Yeasts are unicellular ascomycetes. They reproduce sexually by 2 single cells fusing
together, then undergoing meiosis and then producing spores.
a
b
Figure 5. a) The morel. b) The cup-shaped fruiting body of the scarlet cup fungus.
Basidiomycota (basidiomycetes) – the club fungi
•
About 16,000 species. Include the familiar mushrooms, puffballs, and bracket or shelf
fungi. Called club fungi because they produce club-shaped reproductive structures.
•
Asexual reproduction: Uncommon
•
Sexual reproduction: hyphae from opposite mating types fuse to from a dikaryotic
mycelium (the secondary mycelium) which will then continue growing extensively.
At some point, compact masses of buttons develop along the mycelium. These
buttons will develop into the familiar mushrooms. Mushrooms are composed of a
stalk and cap. Underneath the cap on thin plates of cells are gills. On the gills
develop basidia, special, enlarged club like cells. It is in the basidia where the two
nuclei fuse. The new cell then undergoes meiosis and produces basidiospores. Note
that the basidia are the only diploid structures (Figure 5).
Haploid nuclei
fuse to form
diploid zygote
Mushrooms gills
bear reproductive
basidia
Mushroom
developes from
aggregated hyphae
Compatible hypha
fuse and grow into
mycelium, but
haploid nuclei
within mycelium
remain seperate
Figure 6. The life cycle of a typical basidiomycota
Basidiospores
germinate, forming
haploid hypha
a
b
c
Figure 7. a) Coprinus sp. b) Agaricus sp. C) Amanita sp.
Ecological Importance of Fungi
•
As decomposers fungi breakdown organic matter and release nutrients back to the
environment so that they can be used again
•
Many fungi are parasites on both plants and animals
•
Many form Mutualistic relationships with other organisms
o
Lichens – association between a fungus and a green alga.
o
Mycorrhizae – fungi that form associations with trees and plants
Economic importance of Fungi
•
Yeasts ferment sugar to produce alcohol
•
Yeast through fermentation create air bubbles that causes bread to rise
•
Unique flavors of certain cheeses are produced by fungi
•
Soy sauce is produced by the fermentation of soy beans (via fungi).
•
200 species of edible basidiomycetes (morels, truffles, portabella…)
•
Penicillium is used to produce penicillin, widely used antibiotic
•
Cyclosporine suppress immune responses in patients receiving organ transplants.
•
Some of the compounds produced in hospitals are used in controlled medical
situations (stop uterine bleeding, treat high-blood pressure migraine head-aches).
•
Fungi are also used as biocontrol agent.
•
Other fungi are grown commercially to produce certain chemicals (e.g., citric acid)
Fungal Diseases
•
Many fungi cause many serious plant diseases which on a plant may remain local or
become systemic.
•
Fungi that cause plant diseases will actually invade plant cells
•
Others cause important human diseases such as athlete’s foot, ringworms, vaginal
infections where the infection is superficial; in other cases the infections are
systemic.
Systematics of True Fungi
Kingdom: Fungi
1. Division: Oomycota (Water molds)
Genus: Saprolegnia sp.
2. Division: Chytridiomycota (Chytrids)
Genus: Allomyces sp.
3. Division: Zygomycota (Coenocytic true fungi)
Genus: Rhizopus sp. → bread mold
Genus: Mucor sp. → bread and fruit mold
4. Division: Ascomycota (Sac fungi)
Genus: Saccharomyces sp. → yeast
Genus: Aspergillus sp.
Genus: Peziza sp.
Genus: Mochella sp. → Morel (an edible and tasty fungus)
5. Division: Basidiomycota (Club fungi)
Genus: Agaricus sp. → (edible fungus)
Genus: Coprinus sp. → (edible fungus)
Genus: Fomes sp.
Genus: Amanita sp. → (the most poisonuos species)
Genus: Puccinia sp.
Supplement Division: Deuteromycota (Imperfect Fungi)
•
About 17,000 species.
•
They are called imperfect because they have not been seen to undergo sexual
reproduction.
•
Asexual reproduction: through the formation of conidiophores like ascomycota. Thus
most are probably ascomycota.
Genus: Penicillium sp. → penicillin mold
C. Lichens
About 37 species of Phycopyceae, mostly green algae, (especially Trebouxia and
Trentepohlia genera) and rarely cyanobacteria (especially Nostoc sp.) with about 18.000
species of Mycophyta grow together as lichens. Approximately 25.000 lichens have been
identified so far. Generally Ascomycetes, rarely Basidiomycetes and some imperfect fungi
also go into such associations which called mutualism (Figure 1a,b).
Fungus
→
CO2, H2O
↓
Algae
→
Fungal hyphae
photosynthetic algal cells
Fungal hyphae
↑
O2, food
Fungus
↓
↑
→
b
Figure 1 a, b. Lichen structure and mutualism:
Algae provide O2 and food with photosynthesis to
Mycota, Mycota supply CO2 and H2O to Algae
(Mutualism).
CO2, H2O
a
Lichens generally reproduce asexually by releasing fragments of tissue (soredia).
Soredia grow as a new lichen. In sexual reproduction, only mycota reproduce spores in
apotesiums and peritesiums. Spores
germinate
under
conditions and if
appropriate
spores meet a
suitable alga, they make a new lichen
(Figure 2).
Figure 2. Asexual reproductive structer in
Lichens.
Structurally more complex organization of the mycophyta and the phycophyta results in
Crustose (crustlike), Foliose (leafy) and Furiticose (shrubby) lichen thalli (Figure 3a, b, c).
a
b
c
Figure 3. Growth forms of lichens: a) Crustose (crustlike), b) Furiticose. c) Foliose (leafy)
Ecology of Lichens
Lichens live on bare rocks in tropical as well as in arctic and alpine region. They also
grow on dry, nutrient-poor tree barks and on rocks.
Lichens can grow in extreme climate conditions (there are lichens that survive from
-198 0C to 50 0C). In spite of their general durability to extreme climate conditions most
lichenes are extremely sensitive to air pollution, and for this reason they are indicators of
pollution in the environment.
Importance of Lichens
Lichens are important as food for many arctic animals, such as reindeer. Cladonia
rangiferina (Reindeer Lichen) is aeten by many arctic animals and sometimes by people. A
desert lichen, Lecanora (Manna Lichen) is collected and eaten in Libya. Several substances
extracted from lichens were formerly used in dyeing yarns and as acid-base indicators such as
litmus (Roccella tinctoria and Rocchella fuciforme (Litmus lichens)). Orcein, derived from a
lichen, was once used extensively in cytological preparations for staining chromosomes.
Synthetic dyes have now replaced lichen dyes for commercial and laboratory use. Usnic acid
derived from lichens (especially Usnea sp.) has antibiotic properties againist a number of
fungi and bacteria, including human pathogens. Some lichens (Evernia prunastri (Oak
lichen); Pseudoevernia furfuraceae (tree lichen)) are the sourch of an oily substance used in
perfume industry.
Systematics of Lichens
Division: Lichenes
1. Classis: Ascolichenes (Ascomycetes + Phycophyta or Cyanobacteria)
Evernia sp. (Oak lichen)
→
Foliose (leafy)
Lecanora sp. (Manna lichen)
→
Crustose (crustlike)
Xanthoria sp.
→
Foliose (leafy)
Usnea sp.
→
Furiticose (shrubby)
Rochella sp. (Litmus lichens)→
Foliose (leafy)
Cladonia sp. (Reindeer Lichen)
→ Furiticose (shrubby)
Lobaria sp.
→
Foliose (leafy)
2. Classis: Basidiolichenes (Basidiomycetes + Phycophyta or Cyanobacteria)
Cora sp.
→
Foliose (leafy)
Dictyonema sp.
→
Foliose (leafy)
Supplement Group: Lichenes imperfecti: Unknown and not exactly identified lichens.
CHAPTER III. BRYOPHYTES
• Bryophytes are considered the simples plants because they are the only nonvascular
plants. Because they have no way to transport water, they must remain in moist
environments.
• Bryophytes include 3 groups of plants (mosses, liverworts, and hornworts)
• About 17,000 sp.
Mosses (Phylum Bryophyta)
• About 9000 species
• Because they lack vascular tissues they lack true roots, stems and leaves. They have
rhizoids (root-like structures for anchorage and some water absorption), stem-like
stalks, and leaf-like blades.
• The gametophyte generation is dominant; it is leafy and green. The sporophyte is
dependent on the gametophyte
• Plants bear antheridia and archegonia. Rain water is needed to transport sperm to egg
cells.
• The resulting sporophyte plant develops where the archegonium was at and attaches to
the gametophyte at that point. The sporophyte is composed of three structures.
• Foot – where it attaches to the gametophyte
• Seta – stem-like stalk
• Capsule – the sporangium that contains spore mother cells. These cells will undergo
meiosis to form spores. Later the capsule explodes and the spores are released into the
environment.
• The spores germinate into a
thread of green filamentous
cells called the protonema.
This later will produce buds
where the moss plants will
develop from.
• Mosses colonize moist places
and begin to create an
environment that is suitable for
other plants by creating soil
and breaking down rocks.
Figure 1. Life cycle of a moss
Figure 2. General structures and life cycle in mosses
Liverworts (Phylum Hepaticophyta)
• Like mosses, liverworts lack vascular tissues, and are restricted to moist and damp
environments.
• About 6000 sp.
• Liverworts are either thalloid or leafy. The classical Marchantia that is shown in
textbooks is thalloid
• The thallus consists of lobes of relatively flat photosynthetic tissue. Underneath the
thalli are rhizoids that help anchor the plants. On top of the thalli, liverworts produce
their antheridia and archegonia.
• The life cycle of liverworts is very virtually identical to that of mosses. The only
differences are where the structures are borne and their morphology.
o The gametophyte generation is the dominant
one in liverworts.
o Gametophytes produce antheridia that look
like giant umbrellas and archegonia that
look like coconut palm trees. Sperm cells
produced in the antheridia must travel via
water to the archegonia to fertilize the egg
cells.
o
The resulting embryo, grows into a
sporophyte that is dependent on the
gametophyte nutritionally. It too has a foot,
stalk, and capsule the bares spores.
o Sores are explosively released to start the
new gametophyte generation.
Figure 3. Marchantia sp.
• Liverworts reproduce asexually as well by baring tiny reproductive bodies called
gemae in gemae cups. These cups are located on the thallus.
Hornworts (Phylum Anthocerotophyta)
• About 100 species.
• Hornworts like mosses and liverworts are nonvascular and need to live in moist places
• They resemble liverworts by having a leafy thallus.
• But they differ from both mosses and liverworts in a few respects
o They have a single large chloroplast in the cells
o They archegonia and antheridia are embedded in that thallus
o The sporophytes (which grow out of the thallus) continue to grow and
lengthen from the base for the remainder of the gametophyte’s life.
CHAPTER IV. SEEDLESS (LOWER) VASCULAR PLANTS
Seedless vascular plants include nonflowering plants that have a vascular system of
fluid-conducting (xylem and phloem). The vascular system connects the leaves, roots and
stems.Seedless vascular plants include the divisions Pteridophyta (ferns), Lycodophyta (club
mosses), Psilophyta (whisk ferns), and Equisetophyta (horsetails).
Ferns represent a separate group of seedless plants distinguished by the presence of
megaphylls, which are large leaves with several to many veins. The remaining seedless
vascular plants possess microphylls (small leaves with one vein). However, all seedless
vascular plants possess sporophylls, which are leaflike structures of the sporophyte
generation that bear spores. Sporophylls may be large and have several to many veins (as in
the megaphylls of ferns), or they may be smaller and have one vein (as in the microphylls of
the other divisions of seedles vascular plants).
Division: Pteridophyta (Ferns)
The phylum Pterophyta is a group of non-seed
plants which consists of about 12.000 living species.
Most are found in the tropics where tree ferns may
grow as high as 40 feet.
The stems of ferns which called rhizomes
grow underground. The leaves that called fronds
grow up from the rhizome each spring. Blade is the
flat expanded part of a leaf as distinguished from the
petiole (Figure 1).
Figure 1. The parts of a fern
Reproduction of Ferns
1-The Sporophyte Generation
The plant we recognize as a fern is the
diploid sporophyte generation (Figure 2).
Sori form on the fronds (Photo 1). Each
contains many sporangia mounted on stalks.
Within each sporangium, the spore mother
cells undergo meiosis producing four haploid
spores each.
Photo 1. The sori on the underside of the leaflets of a fern.
When the humidity drops,
The thin-walled lip cells of each sporangium separate.
•
The annulus slowly straightens out. Then the annulus snaps forward expelling the
spores.
2- The Gametophyte Generation
If a spore is blown to a suitable moist location (Figure 2),
•
It germinates into a filament of cells.
•
This grows into a prothallus with
o
rhizoids, which absorb water and minerals from the soil;
o
archegonia, which produce a single egg (by mitosis);
o
antheridia, which form swimming sperm (again, by mitosis).
Figure 2. Fern life cycle
Fertilization
If moisture is plentiful, the sperm swim to archegonia (usually on another prothallus
because the two kinds of sex organs generally do not mature at the same time on a single
prothallus) (Figure 4).
Fertilization restores the diploid number and begins
a new sporophyte generation (Figure 3).
The embryo sporophyte develops a foot that
penetrates the tissue of the prothallus and enables the
sporophyte to secure nourishment until it becomes selfsufficient.
Although it is tiny, the haploid fern prothallus is a
fully-independent, autotrophic plant.
Figure 3. Haploid and diploid stages
Figure 4. Fern life cycle (Fertilization and Meiosis)
Division: Lycodophyta (Club mosses & Spike mosses)
Club mosses grow wild in the wetter parts of Barbados (about 300 miles north of
Venezuela). They are a relic group of plants which most being extinct. There are only two
surviving genera (Selaginella and Lycopodium) today. These plants live near moisture (in
order for their spores to germinate).
Lycopodium sp. are essentially creeping
plants with tiny leaves, termed microphylls, spirally
arranged around the stem. There are separate sterile
and
fertile
leaves
and
the
spore-bearing
(sporophylls) leaves are grouped to form cones or
strobili at the shoot tips (Photo 2).
In Selaginella sp., the sporophyte has a
creeping habit and is dorsiventrally flattened. The
roots are typically borne on a rhizophore which
extends from the stem (Photo 3 and Figure 5).
Photo 2. Lycopodium with
cones
Photo 3. Selaginella serpens
Figure 5. The parts of Selaginella
Division: Equisetophyta (Horsetails)
The horsetails are recognizable by their erect, jointed stems ringed by microphylls
(small leaves at the nodes) and topped by cones (the apical strobilus) (Figure 6 and Photo 4).
Only a single genus Equisetum survives today with a few temperate species.
Figure 6. Equisetum arvense
Photo 4. This is a fertile shoot tip of Equisetum
Division: Psilophyta (whisk ferns)
The whisk ferns (Psilophytes) have
no roots and usually no leaves. Instead of
roots they have rhizomes with absorptive
rhizoids. They live in tropical to sub-tropical
areas and are terrestrial or epiphytic. There
are only 2 genera (Psilotum and Tmesipteri),
and only a few living species (Photo 5).
Photo 5. Pisilotum nudum bearing sporangia
Ecological importance of seedless vascular plants
1. Rhizomes and rhizoids of ferns help to prevent erosion by holding soil together.
2. Ferns help form soil as they decay.
3. Some animals such as muskrats eat seedless vascular plants that grow along stream bank.
Economic importance of seedless vascular plants
1. Some ferns are cultivated in homes, gardens and conservatories and are often used in floral
arrangements.
2. Some fiddleheads are canned or frozen and sold as food (popular in New England and
places in Canada).
3. Seedless plants that died 300 million years ago are responsible for our coal deposits.
CHAPTER V. GYMNOSPERMS
Higher plants are divided into two main groups: angiosperms and gymnosperms.
Angiosperms include all flowering plants which are again divided into monocotyledonous and
dicotyledonous plants. Both gymnosperms and angiosperms have vascular tissue and both
produce seeds. However, the seeds of angiosperms are surrounded by the wall of the ovary of
the flower which forms the fruit, whereas gymnosperms do not possess this structure. Their
seeds are described as naked (Gymnosperm from the Greek: gymnos - naked, sperm - seed).
Botanists place the angiosperms in the group (division) Angiophyta but the Gymnosperms are
separated into four divisions.
Coniferophyta :
The Coniferophyta or conifers, are the most well known and dominant gymnosperms.
This group includes the Pines, Yews, Spruces, Junipers, Cedars etc. The high latitudes of the
northern hemisphere are dominated by extensive forests of conifers. Pines of major economic
importance provide much of the wood and paper pulp used today.
In the pine family (Pinaceae) and other conifer families which produce cones, the
seeds are borne naked on the surface of the scales of the cones. The cone forms a rigid
protection for the seeds. In other families e.g. Yellowwoods (Podocarpaceae) and Junipers
(Cupressaceae) the seeds are surrounded by berry-like structures. Although these may appear
superficially like fruit they are not the same structures as the fruit of angiosperms. Pines,
cedars, spruces and yellowwoods, which belong to the group Coniferophyta or the conifers,
are the largest group of gymnosperms (naked-seeded plants) and have various leaf types.
Pine trees (family Pinaceae) have needle-like leaves which are grouped together in
fascicles and grow from a short branch which grow no longer than one node. The cypresses
and junipers (family Cupressaceae) have very small scale-like leaves which are crowded
along the stem. The leaves of the Ginkgo or Maidenhair tree (the only surviving species of
the group Ginkgophyta) are interesting in that they have dichotomous venation, in other
words each vein divides into two near the leaf margin (Figure 1).
(a)
(b)
(c)
Figure 1. a) A pine have needle-like leaves which are grouped together in fascicles b) A juniper twig covered
with very small scale-like leaves c) A ginkgo leaf showing the dichotomous venation.
Cycadophyta :
The cycads from Southern Africa are slow growing palm-like plants with leaves which
are borne together on the top of the trunk. The seeds are carried on the surface of the scales
of cones in Encephalartos (Photo 1).
Photo 1. Two plants belonging to the Cycadophyta. A Cycas species (left) and another species of cycad (right)
showing a large cone.
Gingkophyta :
This group contains only a single
living species, and
was once widely
distributed in the Northern hemisphere
(Ginkgo biloba). Ginkgo Biloba is one of the
oldest living tree species, dating back over
300 million years, and individual trees can
live for over 1,000 years. It is therefore
referred to as a "living fossil (Photo 2).
Photo 2. Ginkgo Biloba
Gnetophyta :
This is a mixed group of plants with certain characteristics in common with the
Angiosperms (e.g. the xylem contains vessels and they have pollen-producing structures
which superficially resemble stamens). The division includes a genus of tropical lianas
(Gnetum), the joint-firs (Ephedra) and the very strange plant Welwitschia mirabilis which
grows in the Namib Desert in Namibia (Photo 2).
The oldest living organisms on earth are found among the gymnosperms and include
the Welwitschia, some of which are between 1000 and 2000 years old and the Bristle-cone
pine of the south western USA, some of which are estimated to be 4500 years old. The
gymnosperms also contain the tallest trees, the Californian redwoods, which may reach 82 m
in height (Photo 3, 4, 5).
Photo 2. The remarkable (Welwitschia mirabilis) of
the Namib Desert is one of the oldest living plants.
Bottom right are details of the cones. Welwitschia
only
ever
have
two
leaves
which
grow
continuously from the base and slowly decay or are
worn away at the outer edges.
Photo
3.
The
Californian
redwoods
(Sequoiadendron
giganteum ) are the largest living plants. These trees may attain
a height of over 80m.
Photo 4. A Bristle-cone Pine (Pinus longaeva) on a
cliff edge, USA.
Photo 5. Ephedra distachya
CHAPTER VI. FLOWERING PLANTS
(Angiosperms: Anthophyta: Magnoliophyta)
•
Vascular plants that reproduce sexually by forming flowers and afterwards seeds within
fruits.
•
Angiosperms have ovules enclosed within an ovary which will later become the fruit. In
gymnosperms, the ovule is not enclosed.
•
Most successful plant family (235,000 sp)
•
Flowering plants are often divided into two major groups - dicotyledonous and
monocotyledonous plants. Although these two groups are no longer considered valid by
taxonomists, they are useful for gaining a general understanding of how plants function.
Below are the general characteristics of the two groups, note that there are exceptions to all
these characteristics.
Dicotyledonous
One embryo leaf - cotyledon
Tap root system - one main root
with side roots
Leaves with net venation
Secondary growth in stems
Whorls in flowers made up of four
or five parts
Monocotyledons
One embryo leaf or cotyledon
Adventitious root system - no one
root dominant
Leaves with parallel venation
Usually no secondary growth in stems
Whorls in flowers made up of three
parts
Flowering Plant Life Cycle
•
Flowering plants produce sexual organs called flowers which include 4 parts: sepals,
petals, stamens and ovaries.
•
Stamens are the male portion of the flowers. In the anther, which is the yellow sac at the
end of the stamens are several microsporangia. The microsporangia contain spore mother
cells which divide by meiosis to produce haploid spore cells. These spore cells will then
divide once to form an immature male gametophyte (a pollen grain). Pollen grains have 2
nuclei, the generative nucleus (which will later divide to form 2 sperms cells) and the tube
nucleus which will be in charge of creating the tube.
•
The pistil, the female portion of the flower contains the ovary. Ovaries may contain 1 to
main ovules each (structures that contain egg cells and later develop into seeds). Each ovule
has a megaspore mother cell that divides by meiosis to form 4 unequally sized cells (1 very
large). The 3 smaller disintegrates and the 1 becomes the megaspore. This will divided by
mitosis 4 times to form the 8 nucleate embryo sac (7 cells, 8 nuclei), the mature female
gametophyte. One of the cells is the egg cell. Another cell has 2 nuclei called the polar
nuclei.
Figure 1. Basic flower parts
•
Pollination: Insects, wind, or water, transfers pollen to the receptive surface of the pistil
(the stigma)
•
Fertilization: the pollen grain germinates, the pollen tube grows down the style and into
the ovules in the ovaries. The generative nucleus splits into 2 sperms cells. 1 sperms cell
fertilizes the egg cell . The other fuses with the 2 polar nuclei. This is called double
fertilization. It is unique in all of life.
•
The triploid structure now divides to become the endosperm, the nutritive tissue the
developing embryo will feed on. The fertilized egg will divide into an embryo. The entire
ovule becomes the seed. And the ovary becomes the fruit.
•
Sometimes fruits and seeds will develop through a process called apomixis (production of
seeds without the sexual process). This is a type of asexual reproduction.
Success of Flowering Plants
•
Flowering plants are the dominant plant forms on the planet and the most diverse.
•
Yet the have only been around about 100 million years whereas all others have been
around much longer
•
Many factors may account for their success

Production of seeds and their dispersal by animals

Use of pollinators to aid in fertilization

Efficient vascular system and photosynthetic system

Overall adaptability of the sporophyte.
•
Evidence of flowering plants goes back to 127 million years ago (pollen).
•
Closest living relatives are the Gnetophytes (a gymnosperm)
•
Flowering plant once they evolved rapidly took over.
A Survey of Flowering Plant Diversity
•
There are over 300 families of flowering plants, many of which are important to humans.
•
They form the base of many ecosystems.
•
Magnolia family (Magnoliaceae; 220 sp; ex. Southern magnolia and tulip tree): Perhaps
one of the most primitive plant families.
Important ornamentals and timber trees. Have
large showy flowers.
•
Walnut family (Junglandaceae; 50 sp; ex. Walnut, hickories, and pecans): This family is
important because it provides many nuts for both humans and wildlife. It also provides good
lumber.
•
Cactus family (Cactaceae; 2000 sp; ex. Prickly pear cactus and saguaro cactus): An
important component of dry habitats. Their bodies are modified to conserve water and in
some cases retain it. Typically produce very showy flowers. Common house plants
•
Mustard family (Brassicaceae; 3000 sp; ex. Cabbage, broccoli, mustard, etc.). Very
important family as far as human food crops go. Range world wide. Typified by have 4
petals.
•
Rose family (Rosaceae; 3370 sp; ex. Rose, apples, cherries): common ornamental and
fruit family. Flowers typically have 5 petals to many stamens. Fruits include (apples, pears,
peaches, nectarines, cherries, apricots, plums, almonds, strawberries, raspberries,..). Rose
plants are a classic part of many gardens.
•
Pea family (Fabaceae; 17000 sp; ex. Beans, peas, royal poinceana). Contains many food
and feeder crops (beans and soybeans). Many tree members of this family are common
landscape plants for tropical regions
•
Potato family (Solanaceae; 2000 – 3000 sp. Ex. Potatoes, tomatoes, petunias). Also
important food and ornamental family. Many members of this family produce toxic alkaloids,
some of which have been used in medicines.
•
Grass family (Poaceae; 9000 sp. Corn, grasses, sugar cane). The most important crop
family. Without it there would be no major starches (rice, wheat, corn etc). Grasses grow
everywhere in the world
•
Agave family (Agavaceae; 600 sp. Century plants). Important ornamentals and tequila.
Succulent plants of dry regions. Also used to make fibers.
•
Orchid family (Orchidacaceae; 30,000 sp;). Important ornamentals and part of tropical
canopy forests. Provide source of pheromones for many tropical bees.