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Origins of Angiosperms Spring 2010 Outline Origin of the angiosperms Characters of angiosperms Brief history of angiosperm classification Major groups of angiosperms ANITA grade Origin of the Angiosperms Conifers Gnetophytes Ginkgo Cycads Angiosperms ? Progymnosperms

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outline
Outline
  • Origin of the angiosperms
  • Characters of angiosperms
  • Brief history of angiosperm classification
  • Major groups of angiosperms
  • ANITA grade
slide4

Conifers

Gnetophytes

Ginkgo

Cycads

Angiosperms

?

Progymnosperms

(“seed ferns”)

Divergence estimated at

ca. 325 mybp

timing of angiosperm divergences
Timing of Angiosperm Divergences
  • The timing of the origin of the angiosperms still is uncertain, but most would agree on a Triassic or Jurassic initial divergence, although there is no unequivocal fossil evidence
  • A demonstrable “burst” of phylogenetic radiation is found in the fossil record beginning in the mid- to-late Cretaceous, 140 - 100 mybp
slide8

Origin of the Angiosperms

  • pollen grains from ca. 140 mya (early Cretaceous) but already major radiation!
  • earliest flowers 130 mya
  • likely no extant group of seed plants is very closely related to the angiosperms!
slide9

Origin of Angiosperms

  • Cycad-like plants: Bennettitales?
  • large, flowerlike strobili:
    • pollen-producing organs surrounding an axis bearing naked ovules/seeds
slide10

Origin of Angiosperms

Modification of a “seed fern” such as Caytonia?

Caytonia

fossil: ovule

slide11

Origin of Angiosperms

  • Archaefructus
  • ca. 130 mya
  • ancestral flowering plant or
  • extinct off-shoot of an extinct lineage?
  • aquatic plant (dissected leaves)
  • elongate reproductive axes:
    • -paired stamens below
    • -several-seeded carpels above
slide13

Angiosperms (Flowering Plants)

“Dicotyledons”

Magnoliids

Monocots

Eudicots

-- likely evolved WITHIN angiosperms

Reduced male and female gametophytes!

ALSO:

-- nonmotile sperm!

(evolved independently in certain non flowering taxa)

what makes a plant an angiosperm
What makes a plant an angiosperm?
  • Flower (usually with perianth)
  • Carpels with a stigmatic surface for pollen germination; ovules enclosed within carpels; fruit
  • Ovules with two integuments
  • Reduced female gametophyte, usually 8 nuclei in 7 cells – no archegonium
  • Double fertilization with the production of 3N endosperm
  • Stamens with two pairs of lateral pollen sacs (microsporangia)
  • Xylem – most with vessels (evolved within angiosperms)
  • Phloem – sieve tube members with 1 or more companion cells derived from the same mother cell
slide15

Flower

Figure 4.16 from the text

slide16

Spiral undifferentiated

perianth parts = tepals

(plesiomorphic)

slide17

Differentiated sepals and

petals (each in whorls)

(apomorphic)

slide18

Laminar stamens

in basal angiosperms

paired pollen

sacs

connective

microsporangium

filament

slide19

Early carpel with

stigmatic crest…

Figure 4.19 from the text

Figure 4.20 from the text

…to the derived carpel

with a style and an

apical stigma.

slide20

Female gametophyte in angiosperms

-no waiting time as in gymnosperms!

-note 2 integuments (bitegmic; some angiosperm lineages

have lost one integument)

-gymnosperms have

only 1 integument

(unitegmic)

mature ovule

ovule

slide21

Seed development in angiosperms

-no waiting time as in gymnosperms!

double fertilization

seed

slide22

Avocado

(Persea, Lauraceae)

flower

exocarp

mesocarp

endocarp

seed

fruit

slide23

Vessels in Angiosperms

  • are the water (solute) conducting cells of the
  • xylem in most angiosperms
  • ends of cells have openings (perforation
  • plate), cells shorter and wider
  • more efficient, faster rate of flow but more
  • susceptible to air bubbles (embolisms) than
  • tracheids are
  • may have arisen independently in two or more
  • angiosperm lineages but may have had a
  • single origin
slide24

Origin of vessels from tracheids

Figure 4.32 from the text

slide25

Angiosperm phloem

  • sieve tube members + companion cells
  • stm = specialized sugar-conducting
  • cells of the phloem of angiosperms;
  • lack a nucleus at functional maturity
  • cc = parenchyma cells associated
  • with stm
  • -function to load/unload sugars into stm cavity
  • -derived from the same mother
  • cell as its stm

stm

alternative ways of thinking about early angiosperm characters
Alternative ways of thinking about early angiosperm characters…
  • “Old” School (German) - Engler

- “Simple is primitive” (Few floral parts)

- Ancestors are conifers

- Pollination by wind

- Modern relicts = “Amentiferae” (catkins)

  • “New” School (American) – Bessey

- “Flowers with many parts are primitive”

- Ancestors are Cycad-like plants

- Pollination by primitive insects

- Modern relicts = Magnolias and allies

heinrich gustav adolph engler 1844 1930
Heinrich Gustav Adolph Engler(1844-1930)
  • German Botanist at Berlin Botanical Garden-Was the primary European in interpreting the grouping of major angiosperm assemblages-“Few simple flower parts primitive”-Small, unisexual flowers primitive
slide29

Englerian ‘Primitive Taxa’

Juglans sp.

Quercus sp.

“Amentiferae”

Betula sp.

charles edwin bessey 1845 1915
Charles Edwin Bessey(1845-1915)

-Botanist at Iowa State University from 1869-1884 (left in 1884 to teach in Nebraska)-Was a “major player” in interpreting and understanding angiosperm evolution-“Many flower parts primitive”

Bessey Hall

Iowa State University

slide31

Bessey’s “Cactus”

(1915)

Placed plant groups

with many floral

parts in a basal

position as the

‘ancestral’ forms.

Outlined ‘dicta’ for

the construction of

phylogenies using the

evolutionary trends in

character changes.

Polypetalous flowers,

insect pollination,

cycad-like ancestors

slide32

Besseyan ‘Primitive Taxa’

Nymphaeaceae

Magnoliaceae

major groups of angiosperms
Major Groups of Angiosperms
  • Basal Angiosperms (ANITA grade)

- Amborellaceae

- Nympheaceae

- Illiciaceae

  • Magnoliid Complex (incl. “paleoherbs”)

- Magnoliales

- Piperales

- Winterales

  • MONOCOTS
  • EUDICOTS (tricolpates)
major groups of eudicots
Major Groups of Eudicots
  • Basal Tricolpates

- Ranunculales and allied families

  • Caryophyllales & Saxifragales
  • Rosid Clade

- Basal Rosids

- Eurosids I (Fabids)

- Eurosids II (Malvids)

  • Asterid Clade

- Basal Asterids

- Euasterids I (Lamiids)

- Euasterids II (Campanulids)

anita grade
ANITA grade
  • Amborella (Amborellales)
  • Nymphaea (Nymphaeales)
  • Illicium (Austrobaileyales)
  • Trimenia (Austrobaileyales)
  • Austrobaileya (Austrobaileyales)
slide37

ANITA grade

Figure 9.1 from the text

> 125 mybp

Grade = a polyphyletic (or

paraphyletic) group whose

members share a similar

level of morphological or

physiological complexity.

> 140 mybp

slide38

Major Angiosperm Clades

Amborellaceae

Nymphaeales

Austrobaileyales

MAGNOLIID

COMPLEX

MONOCOTS

EUDICOTS

[TRICOLPATES]

“BASAL FAMILIES”

Soltis et al. 2000,

APG II 2002,

Judd et al. 2002

basal angiosperms amborellaceae
Basal Angiosperms: Amborellaceae
  • New Caledonia
  • Understory shrub; plants dioecious
  • 1 species (monotypic): Amborella trichopoda
  • Leaves simple, evergreen
  • Flowers small, unisexual: ♀ apocarpous, with stigmatic crests; ♂ with laminar stamens
  • Significant features: Most basal of all flowering plants; no vessels in wood
  • Special uses: (none)
basal angiosperms nymphaeaceae water lily family
Basal Angiosperms:Nymphaeaceae(Water Lily Family)
  • Widespread, tropics to temperate regions
  • Aquatic rhizomatous herbs, sap milky
  • 70 species; 8 genera
  • Flowers: many parts; laminar stamens; “floating”; colorful perianth; “beetle” syndrome
  • Special uses: ornamentals; sacred lotus
  • Required taxa: Nymphaea (water lily)
slide42

Basal Angiosperms:Nymphaeaceae (Water-lily Family)

  • numerous petals, stamens, carpels
  • laminar stamens
  • pollen monosulcate
  • stigma discoid, radiating
  • berry-like fruit, dehiscent
  • perisperm
  • usually lack vessels (or have tracheid-like vessels)
basal angiosperms illiciaceae star anise family
Basal Angiosperms:Illiciaceae(Star Anise Family)
  • SE Asia, SE USA and Caribbean
  • Trees and shrubs
  • 1 genus, Illicium; ca. 40 species
  • Flowers: many floral parts/tepals; 1 ovule/carpel
  • Special uses: star anise (spice)
  • Required taxa: (none)
illicium star anise
Illicium – Star Anise

Illicium parviflorum

Illiciumfloridanum

as we venture through the various major groups of angiosperms
As we venture through the various major groups of angiosperms…
  • Identify the plesiomorphic characteristics associated with particular groups and note their apomorphies (if any) as well.
  • Try to associate “syndromes” of characteristics with each group (make note of special characters occurring together).
  • One good way to study is to write keys to the groups we cover in any given unit.
  • Names of groups are important! Learn to spell and say them!
  • Ask questions!!