Chapter 30: Plant Evolution and Classification

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Chapter 30 Plant Evolution and Classification
30-1 Overview of Plants
30-2 Nonvascular Plants
30-3 Vascular Plants
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Revisiting Evolution

• The first true plant is thought to have been
  similar to a green alga, with adaptations that
  enabled it to survive the dry conditions on land.

Assessing Prior Knowledge

• Explain how successive generations become
  adapted to different conditions and evolve into
  different species.

• Describe what types of data are used to
  construct a phylogenetic tree.

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30-1 Overview of Plants
I. Adapting to Land (from green algae?)

• Terrestrial life evolved 430 m.y.a. (following
  ozone) and at one point small, club-shaped plants
  began to grow in the mud at waters edge.

• Like green algae, plants possess chlorophyll,
  store energy as starch, and have cellulose making
  up their cell walls.

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(A) Preventing Water Loss

• Benefits of migrating? More exposure to
  sunlight, increased CO2 levels, and greater
  supply of nutrients. Tradeoff? Desiccation.

(1) Cuticle (an early adaptation to life on land)

• A waxy protective covering on plant surfaces
  that prevents water loss (balanced out by stomata
  to exchange gases through cuticle)

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(B) Reproducing by Spores and Seeds

• Evolved to aid terrestrial plant reproductive
  cells from drying out.

(1) Spore (widespread water-resistantprimitive
dispersal strategy)

• Haploid reproductive single cell surrounded by a
  hard outer wall.

(2) Seed (more evolved dispersal strategy and is
multicellular)

• Embryo surrounded by a protective coat and
  contains an endosperm.

(3) Endosperm

• Tissue that provides nourishment for the
  developing plant embryo.

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(C) Transporting Material throughout the Plant

• As a multicellular organism, differentiated
  plant cells need to share resources to grow,
  divide, and carry out metabolic activity.

(1) Vascular Tissue (2 types more evolved
terrestrial plant species)

• Specialized plant tissue that transports water
  and dissolved substances.

(2) Xylem

• Vascular tissue carrying water and inorganic
  nutrients in one direction, from the roots to the
  stems and leaves.

(3) Phloem

• Vascular tissue carrying organic compounds
  (carbohydrates), and some inorganic nutrients in
  ANY direction, depending on the plants needs.

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(4) Woody Tissue (advantage in growing to greater
heights, more sunlight)

• Formed from several layers of xylem, usually
  concentrated in the center of the stem (generally
  brown and rigid)

(5) Herbaceous Tissue (shorter plants, non-woody
plants)

• Vascular tissue that is NOT surrounded by
  schlerenchyma cells, making the stems of
  herbaceous plants soft, green, and flexible.

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II. Classifying Plants

• Kingdom Plantae is divided into 12 phyla (a.k.a.
  divisions) divided into 3 groups based upon the
  presence of vascular tissue.

(1) Nonvascular Plants (3 phyla, less
diversified, no xylem or phloem)

• More primitive plants that lack true vascular
  tissue, roots, stems, and leaves.

(2) Vascular Plants (9 phyla, more diversified)

• More recently evolved plants that possess
  vascular tissue, roots, stems, and leaves.

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Non-Vascular Plants Non-Vascular Plants
Mosses 10,000
Liverworts 6,500
Hornworts 100
Vascular Plants - Seedless Vascular Plants - Seedless
Whisk ferns 10 - 13
Club-mosses 1,000
Horsetails 15
Ferns 12,000
Seed Plants - Gymnosperms Seed Plants - Gymnosperms
Conifers 550
Cycads 100
Gingko 1
Gnetae 70
Angiosperms Angiosperms
Flowering plants 235,000
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(3) Seed-Bearing Plants

• More evolved than seedless plants (spore-bearing
  plants), include four phyla of gymnosperms and
  one phylum of angiosperms.

(4) Gymnosperms (non-flowering plants)

• Class of seed-bearing plants that produce seeds
  that are NOT enclosed in fruits (e.g., pine trees)

(5) Angiosperms (flowering plants)

• Class of seed-bearing plants that produce seeds
  within a protective fruit (e.g., apple and orange
  trees)

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(A) The Fossil Record of Plants

• Strong evidence suggest modern plants evolved
  from an ancestor of green alga
• (e.g., BOTH have the same photosynthetic
  pigments, chlorophylls a and b, both store energy
  as starch, and both have cell walls made of
  cellulose)

• Suggested Evolutionary Order
• Algal Ancestors ?
• Nonvascular Plants ?
• Seedless Vascular Plants ?
• Gymnosperms ?
• Angiosperms

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(B) Alternating Life Cycles

• All plants maintain a life cycle that involves
  TWO phases, named after the type of reproductive
  cells the plant produces in each phase.

(1) Sporophyte (diploid plant2N, pine oak
trees are large sporophytes)

• Plant producing spores, known as the sporophyte
  generation/phase and is the dominant phase in
  VASCULAR plants.

(2) Gametophyte (haploid plant1N)

• Plant producing gametes (egg and sperm cells),
  known as the gametophyte generation/phase and is
  the dominant phase in NONVASCULAR plants.

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(3) Alternation of Generations (NOT found with
green algae)

• A type of life cycle which alternates between
  the sporophyte and gametoyphyte phases.

• NOTE The gametophyte makes gametes, which
  combine to make a diploid zygote, of which
  divides to form a sporophyte plant (2N).

• Sporophyte (through meiosis) produces haploid
  spores (1N)these spores are released by most
  seedless plants BUT are retained by seed-bearing
  plants.

• The life cycle begins again when spores divide
  by mitosis to form new gametophytes.

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30-2 Plants and the Environment
I. Classifying Bryophytes (the 3 phyla of
primitive nonvascular plants)

• Require water to reproduce sexually because the
  sperm must swim through water to an egg. (asexual
  production of haploid spores does not require
  water)

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(A) Phylum Bryophyta (dominant-gametophyte,
water-dependent reprod.

• Includes about 10,000 species of mosses
  (gametophytes).
• (NOTE The leafy carpet of moss gametophytes is
  topped by sporophytes that, when mature, release
  haploid spores which grow into a new generation
  of gametophytes.)

(1) Rhizoids (lack true vascular tissue)

• Attaches the bryophyte to the soil (anchoring)
  and assists with the absorption of water and
  inorganic nutrients.

(2) Sphagnum (peat moss)

• Produces an acid that slows down decomposition
  in the swamp-like bogs. (also widely used by
  florists for packing bulbs and flowers for
  shipping)

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(B) Phylum Hepatophyta and Anthocerophyta

• Includes about 6,500 and 100 species of
  liverworts and hornworts that also grow in moist,
  shady habitats.

(1) Thalloid (some liverwort species)

• A flat body with distinguishable upper and lower
  surfaces (most liverworts have thin, transparent
  leaflike structures arranged along a stemlike
  axis).

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30-3 Vascular Plants
I. Seedless Vascular Plants

• Four phyla (fern allies and ferns), dominated
  the Earth until about 200 m.y.a. relying upon
  spores as the mobile sexual reproductive cells.

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(A) Phylum Psilotophyta (e.g., whisk ferns)

• Produce reproductive structures on the ends of
  forked branches and lack true roots or leaves
  (can grow up to a foot tall).

• Include whisk ferns which are epiphytes,
  growing on other plants in a commensalistic
  manner.

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(B) Phylum Lycophyta (e.g., club mosses,
miniature pine trees)

• Evergreens that produce spores in cones and have
  true roots (can grow only about 2 inches tall).

• Include resurrection plant (Selaginella
  lepidophylla) native to the American Southwest,
  which turns brown and curls up in a ball during a
  drought but comes back alive within a few hours
  of becoming moist.

(1) Strobilus (cone)

• A cluster of sporangia-bearing modified leaves.

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(C) Phylum Sphenophyta (e.g., Horsetails or
Equisetum)

• Jointed stemmed plants with outer cells of stems
  containing silica, a major component of sand,
  SiO2 (can grow about 2-3 feet tall)

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(D) Phylum Pterophyta (e.g., ferns)

• Leaves with spores on the underside and an
  underground stem are present with true ferns (can
  grow from 1 inch to 82 feet talltree ferns).

• A diverse group including some floating plants
  as well as some inhabitants of the Arctic Circle
  and desert regions. (evolved around 350 m.y.a.)

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(1) Rhizome (horizontal root)

• Fibrous stem that grows horizontally underground

(2) Fiddleheads

• Tightly coiled new (immature) leaves of ferns

(3) Fronds

• Mature leaves that develop sori (pl. of sorus)
  on the underside where haploid spores develop.

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II. Vascular Seed-Bearing Plants

• The mobile sexual reproductive part of seed
  plants is the multicellular seed, an evolutionary
  success story of adaptation and germination.

(1) Germination

• Abiotic conditions favor growth, a seed sprouts
  as the embryo begins to divide and grow into a
  new seedling.

(2) Seedling

• New young plant that has emerged as an embryo
  through the seed coat.

(3) Cone (found among the 4 phyla of gymnosperms)

• Reproductive structure made of hard scales,
  bearing the seeds on the open surface. (serve
  similar roles in gymnosperms as flowers do for
  angiosperms)

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(A) Phylum Cycadophyta (100 species remaining)

• Gymnosperms native to the tropics and have
  fern-like, leathery leaves at the top of a short,
  thick trunk. (male and female plants bear large
  cones)

• Some cycads are suggested to have been alive for
  over a thousand years, and grow very slowly yet
  sometimes large60 feet in height.

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(B) Phylum Ginkgophyta (1 species remaining,
Ginkgo biloba)

• Fan-shaped leaves that fall from the tree at the
  end of each growing season, with large seeds and
  tall heights80 feet. (NOTE Most gymnosperms are
  evergreens and retain their leaves year-round)

• Ginkgos are known as the living fossil because
  it closely resembles fossil ginkgoes that are 125
  million years old.

(1) Deciduous

• Trees that lose their leaves at the end of the
  growing season.

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(C) Phylum Coniferophyta (1,000 species
remaining)

• Woody plants, most with needles or scale-like
  leaves, and usually bearing both male (staminate)
  and female (ovulate) cones.

• Conifers include pines, cedars, redwoods, firs,
  spruces, junipers, cypresses and sequoias.

• Most massive tree is Sequoiadendron giganteum,
  the Giant Sequoia, which reaches heights of 350
  feet tall and weighs approximately 6,200 tons.

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(D) Phylum Gnetophyta (20 species remaining,
Ephedra genus)

• Unusual group of gymnosperms that have vascular
  systems that more closely resemble angiosperms
  with jointed stems.

• Examples include Ephedra, a genus of desert
  shrubs and Welwitschia, a another genus found in
  the deserts of southwestern Africa.

(1) Ephedrine

• Decongestant drug (also a stimulant) derived
  from the cones of plants belonging to the Ephedra
  genus.

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(E) Phylum Anthophyta (240,000 species, the
flowering plants)

• Angiosperms, the other class of seed-bearing
  plants, are characterized by the presence of a
  flower and fruit.

• Angiosperms can be herbaceous plants like
  violets or shrubs like rose bushes. Still others
  are vines, like grapes and ivy.

• Oak, aspen, and birch trees are all flowering
  plants that have woody stems, although the small
  flower are almost undetectable. Likewise,
  grasses are also angiosperms, but their small,
  highly modified flowers are rarely
  noticed(Worlds Largest Flower is made by
  Rafflesia arnoldii)

(1) Ovary

• The female part of the flower that encloses the
  egg, and when ripened, becomes a fruit of the
  plant.

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(F) The Evolution of Angiosperms (why such
success?)

• In angiosperms, seeds germinate and produce
  mature plants, which in turn produce new seeds,
  all in ONE growing seasonhuge advantage over
  gymnosperms which often take ten or more years to
  reach maturity and produce seeds.

• More efficient vascular system (and more
  mycorrhizae) and an advanced and diversity of
  seed dispersal strategiesoften with animal
  carriers.

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(G) Monocots and Dicots (all angiosperms are
divided into two classes)

• Flowering plants are classified based upon the
  number of cotyledons present in the plant embryo,
  as well as a few other features.

(1) Cotyledons

• Seed leaves found in in the plant embryo, either
  one (monocot) or two (dicot) leaves are present.
  (NOTE By comparison, gymnosperms typically have
  two or more cotyledons)

(2) Parallel Venation (monocot leaves)

• Most mature monocot leaves have several main
  veins or bundles of vascular tissue running
  roughly parallel to each other.

(3) Net Venation (dicot leaves)

• Most dicots have one or more non-parallel main
  veins that branch repeatedly, forming an
  interconnected network.

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