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Topic 3: Plant Diversity I (Ch. 29)
Kingdom Plantae – general characteristics
A. eukaryotic, multicellular, with cell walls rich in cellulose
B. most are photosynthetic, with chloroplasts containing chlorophylls a and b and carotenoids
C. all have alternation of generations
D. dominate nearly all terrestrial communities (exceptions in tundra); major producers in most of these habitats
E. source of food, shelter, clothing, much of the atmosphere’s oxygen
F. ~300,000 described living species in 10 phyla
G. two groups:
1. nonvascular plants (a grade) and vascular plants (a clade)
2. vascular plants divided into those without seeds (a grade) and those with seeds (a clade)
Evolutionary origin and adaptations to land
A. related to green algae
1. chloroplast similarity
2. cellulose in cell walls
3. starch as energy reserve
4. formation of cell plate during division (found in plants and some green algae)
5. genetic similarities (especially ribosomal RNA sequence); plant clade is ~500 million years old
6. distinguished from green algae because diploid form always begins development within tissues of a haploid form, and
always have heteromorphic (different-looking) haploid and diploid forms
7. also distinguished by adaptations to survival on land, including protecting embryos
B. revised classification: Kingdom Viridiplantae
1. cladistic analysis shows no clear division between plants (traditional Kingdom Plantae) and green algae (traditional
Phylum Chlorophyta)
2. instead, traditional land plants together with some green algae apparently form a monophyletic group called
3. the Streptophyta together with the rest of the green algae apparently form a monophyletic group, the proposed (and
increasingly accepted) Kingdom Viridiplantae (or Viridaeplantae)
C. adaptations to land
1. plants are primarily terrestrial – few aquatic species
2. plants likely first terrestrial organisms
3. cell wall helps prevent water loss (desiccation)
4. embryos (young sporophyte plants) protected by some sort of covering to protect against things like desiccation
5. most plants have a waxy cuticle – on exposed surfaces, relatively impermeable; prevents most water loss
6. cuticle creates a problem with gas exchange, so most plants have stomata (singular: stoma)
 pores that can be opened and closed for gas exchange
 up to thousands per square centimeter on leaves
 closing helps prevent water loss
 must open to let carbon dioxide in, oxygen out
7. mycorrhizal relationships with fungi
 found in about 90% of plant species, some absolutely required
 may help some with water uptake
 help tremendously with nutrient uptake
8. other adaptations in some plants
 vascular tissue and related structures (roots, shoots, leaves)
 seeds
 flowers and fruits
III. Plant Life Cycles
A. alternation of generations – mitosis in both haploid and diploid generations
1. sporophyte = multicellular diploid organism; makes spores via meiosis
2. gametophyte = multicellular haploid organism; makes gametes via mitosis
3. plants make meiospores, but never mitospores
4. meiosporangia in sporophyte produces diploid meiospore mother cells (meiosporocytes)
5. meiosporocyte undergoes meiosis to produce four haploid meiospores
6. every “meio-” above is often left off since there are no mitospores; thus, sporangia, spore mother cells, sporocytes, and
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meiospores divide by mitosis, forming gametophyte
gametophyte produces haploid gametes in special gametangia structures in some plants
 antheridium – male gametangia, make sperm
 archegonium – female gametangia, make eggs
9. sperm and egg fuse inside archegonium to form diploid zygote
10. zygote grows into sporophyte; young sporophyte = embryo
11. other activities occur in some groups, these will be discussed when those groups are covered
12. evolutionary trend from “lower” to “higher” plants is a reduction of the gametophyte generation and an expansion of the
sporophyte generation, with more protection of the embryo
 nonvascular plants (mosses, liverworts, hornworts) – gametophyte is green, free-living, dominant generation
 seedless vascular plants (ferns and fern allies) – gametophyte is usually green and free-living, but sporophyte is
dominant generation
 vascular seed plants (gymnosperms and angiosperms) – gametophyte is nutritionally dependent on sporophyte, or
may be saprobic (deriving energy from nonliving organic matter); sporophyte is dominant generation
IV. Nonvascular Plants
A. plants lacking specialized tubes for conducting water and nutrients (that is, lacking vascular tissue)
B. gametophytes photosynthetic and free-living; dominant generation
C. sporophytes are attached to and dependent on gametophytes
D. primitive; likely the modern plants most similar to the “first plants”
E. require external water for sperm to reach eggs for sexual reproduction (swimming sperm)
F. no true leaves, stems, or roots (vascular tissue required for true leaves, stems, and roots)
G. small; rarely more than 7 cm tall
H. most common in and mostly limited to moist places
I. sometimes called bryophytes
J. three phyla:
1. Phylum Hepatophyta – liverworts
2. Phylum Anthocerophyta – hornworts
3. Phylum Bryophyta – mosses
Phylum Hepatophyta – liverworts
A. some with flattened bodies (thalli) with lobes resembling liver; “wyrt” is old English for plant; thus, “liverwort”
B. thalloid forms only 20% of phylum; rest look like mosses
C. simpler than mosses
1. gametophytes develop almost directly from spores (reduced protonema)
2. gametophyte growth is prostrate (flat), not erect
3. rhizoids are one-celled
D. sexual reproduction similar to that in mosses; two small differences:
1. antheridia on stalks called antheridiophores
2. archegonia on stalks called archegoniophores
E. asexual reproduction occurs in thalloid forms from gemmae splashed out of gemma cups on “leaves”
F. about 9,000 living species
VI. Phylum Anthocerophyta – hornworts
A. thalloid gametophytes (look much like thalloid liverworts)
B. cells typically have a single chloroplast, very much like the chloroplast of green algae
C. sporophyte partially independent from gametophyte
1. green; photosynthetic
2. functional stomata
3. still embedded in gametophyte, gets some nutrition from it
D. about 100 living species
VII. Phylum Bryophyta - mosses
A. small “leaves” arranged spirally or alternately around a stem-like axis
B. “leaves” not true leaves; only one cell thick, except at midrib
C. anchored to substrate with root-like rhizoids (not true roots; no vascular tissue, little water absorption)
D. most water travels up outside of plant by capillary action
E. sexual reproduction
1. male antheridia and female archegonia on same or separate plants
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sperm made in antheridia swim to archegonia (using flagella to move through dew or rainwater)
sperm unites with egg in archegonium, forming diploid zygote
zygote undergoes mitotic divisions and develops into sporophyte
 slender stalk with swollen capsule (sporangium) at tip
 base imbedded in gametophyte
 dependent on gametophyte for nutrients
5. spore mother cells in sporangium produce haploid spores
6. at maturity, outer covering of sporangium pops off, releasing spores
7. spores in right (mainly damp) environment grow into protonemata (singular protonema)
8. buds from a protonema become new gametophyte plants
1. about 15,000 living species
2. can survive some drought conditions, but not found in deserts
3. most are very sensitive to air pollution, good indicators of air quality
4. important producers in some habitats such as bogs, Arctic and Antarctic
5. most abundant plants in Arctic and Antarctic
6. peat mosses (Sphagnum) found in peat bogs
 bogs are wetlands with very acidic, water-logged soils
 in bogs where Sphagnum grows abundantly, dead Sphagnum builds up as peat
 “peat bogs” are abundant:
about 1 billion acres of peat bogs in world (northern hemisphere mostly)
 ~1% of Earth’s land surface!
 harvesting peat is an important industry in northern temperate zone (Canada, Denmark, Sweden, etc.)
 peat is used as a soil conditioner or potting mix for good water-holding capacity (peat absorbs 25x weight in
 peat can also be used as fuel
 peat industry is worth many millions of dollars a year
 slow decomposition in peat bogs make them excellent archeological sites
 bodies and artifacts buried in bogs are often well-preserved (“Bog people”)
 allows archeologists to study vanished societies
VIII. Vascular Plants (overview) – plants with xylem and phloem – 7 to 9 living phyla, depending on who you talk to
A. able to dominate most terrestrial habitats because of vascular tissues, waxy cuticle, and stomata
B. conducting tissues (xylem and phloem) called vascular tissues
1. cylindrical or elongated cells that form network throughout plant
2. xylem
 conducts water and dissolved minerals upward
 typically dead cells
 typically at least partially lignified (having lignin, a highly branched polymer that makes cell wall more rigid)
3. phloem
 transports carbohydrates in solution throughout plant (down and up)
 living cells
4. only with vascular tissue do you have true leaves, stems, and roots
C. sporophyte dominant
D. vascular tissue is usually only found in the sporophyte generation
E. seeds (when present) are highly resistant structures that increase ability of developing embryos to survive on land
F. divided into seedless and seed-forming groups; seed-forming phyla covered in future outlines
IX. Seedless Vascular Plants (ferns and fern allies)
A. sporophyte dominant and can grow independent of gametophyte in all
B. gametophyte small, reduced, but still able to grow independent of sporophyte in all
C. importance: dominated land during Carboniferous Period (354-290 million years ago), becoming a source of coal
1. coal is incompletely decomposed, highly compressed, carbon-rich rock derived mainly from the bodies of ancient
seedless vascular plants (a type of “fossil fuel”)
2. fossil coal swamps are full of extinct plants
3. coal is a vital source of energy; burned for heat and for producing electricity (over half of U.S. electric production)
D. at least 3 extinct phyla represented in the fossil record; one will be covered, Phylum Rhyniophyta
E. 4 phyla with living members
1. Phylum Lycophyta
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Phylum Pterophyta
Phylum Psilophyta (some group with Pterophyta; do fall in a clade with that group and Arthrophyta)
Phylum Arthrophyta (some group with Pterophyta; do fall in a clade with that group and Psilophyta)
extinct Phylum Rhyniophyta – oldest vascular plant fossils (Cooksonia, 420 MYA)
A. branching axis; no leaves or roots
B. only a few centimeters tall
C. sporangia at ends of branches
D. appearance much like that of modern-day whisk ferns
E. homosporous – only one spore type, so only one gametophyte type
XI. Phylum Lycophyta – club mosses
A. ~1000 living species; worldwide, but most in tropics and moist temperate regions; many species endangered
B. includes “resurrection plants”
C. fossil record includes tree-like forms that died out about 270 MYA
D. apparently evolved separately from the other seedless vascular plants
E. small, resembling mosses (but vascular with dominant sporophyte)
F. leafy stems usually less than 30 cm long
G. their leaves are also called microphylls, with very little vascular tissue (just a single vein); other vascular plant leaves have
much more complex vascular tissue networks
H. homosporous and heterosporous genera
1. heterosporous – plant makes two types of meiospores, resulting in two types of gametophytes
2. megaspore is larger of the two; grows via mitosis into the female gametophyte
3. microspore is smaller of the two; grows via mitosis into the male gametophyte
I. sexual reproduction similar to that of ferns
J. sporangia grow from specialized leaves called sporophylls; sporophylls are clustered in a cone-like strobilus
XII. Phylum Pterophyta – ferns
A. somewhat complicated phylogeny; we will visit the tree of life in class to discuss this
B. fossils date to as long as 375 MYA (important fossil fuel source)
C. ~12,000 living species; throughout world, but ¾ of species tropical
D. most leafy, but some tree ferns
E. most are homosporous, but some are heterosporous
F. life cycle similar to moss except decreased gametophyte, independent and dominant sporophyte
1. gametophyte
 germinating spore divides by mitosis and forms multicellular protonema
 protonema grows into mature gametophyte called prothallus
 typically heart-shaped; mostly one-cell thick
 has rhizoids
2. gametes produced in male antheridia and female archegonia on same or separate prothalli
3. sperm made in antheridia swim to archegonia (using flagella; need outside water source to swim in)
4. sperm unites with egg, forming diploid zygote
5. zygote undergoes mitotic divisions and develops into sporophyte
 sporophyte grows out gametophyte and takes over (larger, vascular, photosynthetic, responsible for all of own
 typically have horizontal, underground stem (rhizome)
 leaves (called fronds) develop from rhizome as coiled “fiddleheads”
 form stalked sporangia in clusters called sori, typically on the backs of fronds
6. spore mother cells in sporangium produce haploid spores
7. at maturity, outer covering of sporangium snaps off, catapulting spores
8. spore in right (mainly moist) environment will germinate
XIII. Phylum Psilophyta – whisk ferns
A. probably form a monophyletic group with ferns and horsetails; some group these within the fern phylum
B. simplest living vascular plants
1. no true roots or leaves – leaf-like enations and such sometimes present
2. forking green stems (photosynthetic; true stems)
C. sexual reproduction much like ferns (have antheridia and archegonia, swimming sperm that need outside water, etc.)
D. all are homosporous
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E. like ferns, sporophyte is dominant generation
F. gametophytes small, colorless
1. in soil beneath sporophytes
2. associated with fungi
3. saprobic or parasitic
4. some have elements of vascular tissue (only gametophytes known to have this)
G. tropical and subtropical
H. only 6 known living species
XIV. Phylum Arthrophyta – horsetails (alternative phylum names: Sphenophyta; Equisetophyta)
A. probably form a monophyletic group with ferns and whisk ferns; some group these within the fern phylum
B. 15 known living species, all in genus Equisetum
C. most <1 m tall, some 3 m tall; widely scattered in damp regions throughout the world
D. fossil record back to 300 MYA
1. once much more diverse and dominant
2. fossil record includes tree-like forms as tall as 30 m
E. sporophyte dominant
1. branching underground rhizomes with roots at their nodes
2. hollow, ribbed, jointed, photosynthetic stems
3. whorls of scale-like, nonphotosynthetic leaves at nodes on stems
4. some have whorls of photosynthetic branches at nodes as well
5. stems hollow
6. silica deposits in some epidermal cells (stiffens; protects from predators)
7. some are called “scouring rushes” because they were used by pioneers for scrubbing dishes
F. most are homosporous
G. sexual reproduction similar to that of ferns
H. sporangia on underside of stalked structures called sporangiophores
I. sporangiophores are clustered in a cone-like strobilus at a stem tip
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