Origins of Angiosperms - PowerPoint Presentation

Slide1

Origins of Angiosperms

Spring

2014Slide2

OutlineOrigin of the angiosperms

Characters of angiosperms

Brief history of angiosperm classification

Major groups of angiosperms

ANITA gradeSlide3

Origin of the AngiospermsSlide4

Conifers

Ginkgo

Cycads

Gnetophytes

Angiosperms

Divergence estimated at

ca. 325

mybp

Progymnosperms

(“seed ferns”)Slide5

Geologic TimeSlide6

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 mybpSlide7

Figure 7.1Slide8

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/seedsSlide10

Origin of Angiosperms

Modification of a “seed fern” such as

Caytonia

?

Caytonia

fossil: ovuleSlide11

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 aboveSlide12

Characters of AngiospermsSlide13

Fig. 6.1Slide14

What makes a plant an angiosperm?

Flower

(usually with perianth)

Carpels

with a stigmatic surface for

pollen tube

germination; ovules enclosed within carpels; fruit

Ovules with two integumentsReduced female gametophyte, usually 8 nuclei in 7 cells – no archegonium

Double fertilization with the production of 3N endospermStamens with two pairs of lateral pollen sacs (microsporangia);

pollen (male gametophyte) 3-nucleateXylem – most with vessels (evolved within angiosperms)

Phloem – sieve tube members with 1 or more

companion cells derived from the same mother cellSlide15

Flower

Figure 6.2Slide16

Spiral undifferentiated

perianth parts = tepals

(plesiomorphic)

Magnolia

MagnoliaSlide17

Differentiated sepals and

petals (each in whorls)

(apomorphic)

AbutilonSlide18

connective

microsporangium

filament

Laminar stamens

in basal

angiosperms

(

plesiomorphic

)

paired pollen

sacsSlide19

Early carpel with

stigmatic

crest

(

plesiomorphic

)…

…to the derived carpel

with a style and an

apical

stigma (

apomorphic

).

Figure 6.9 from the textSlide20

Female gametophyte in angiosperms

ovule

-no waiting time as in gymnosperms!

-note 2 integuments (bitegmic; some angiosperm lineages

have lost one integument)

-gymnosperms have

only 1 integument

(unitegmic)

mature ovuleSlide21

And it’s off

to the races!

Indirect

pollination

(due to presence

of carpels)Slide22

-no waiting time as in gymnosperms!

Seed development in angiosperms

seed

double fertilizationSlide23

Avocado

(

Persea

, Lauraceae)

seed

endocarp

mesocarp

exocarp

pericarp

Flower

fruitSlide24

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

Vessels in AngiospermsSlide25

Origin of vessels from tracheids

Figure 6.16B from the textSlide26

Angiosperm phloem

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

sieve tube members

+

companion cells

stmSlide27

Brief history of angiosperm classificationSlide28

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

Slide29

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 primitiveSlide30

Englerian ‘Primitive Taxa’

“Amentiferae”

Quercus sp.

Juglans sp.

Betula sp.

Slide31

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 UniversitySlide32

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 ancestorsSlide33

Besseyan ‘Primitive Taxa’

Nymphaeaceae

MagnoliaceaeSlide34

Figure 6.1 from the textSlide35

Major Groups of Angiosperms

Basal Angiosperms (ANITA grade)

-

Amborellaceae

-

Nympheaceae

-

Illiciaceae

Magnoliid Complex -

Magnoliales - Piperales

-

Winterales

MONOCOTSEUDICOTS (

tricolpates) Slide36

Major Groups of Eudicots

Basal

Eudicots

-

Ranunculales

and allied families

Caryophyllales

& Saxifragales

Rosid Clade - Fabids

- Malvids

Asterid Clade

- Basal Asterids

-

Lamiids - CampanulidsSlide37

ANITA gradeA

mborella

(Amborellales)

N

ymphaea

(Nymphaeales)

I

llicium (Austrobaileyales)Trimenia

(Austrobaileyales)Austrobaileya (Austrobaileyales)Slide38

ca. 125 mybp

Fig. 6.1

Grade

= a paraphyletic (or

Polyphyletic) group whose

members share a similar

level of morphological or

physiological complexity.

ANITA Grade

or “basal”

angiospermsSlide39

Major Angiosperm Clades

Amborellaceae

Nymphaeales

Austrobaileyales

MAGNOLIID

COMPLEX

MONOCOTS

EUDICOTS

[TRICOLPATES]

ANITA grade (basal groups)

Soltis et al. 2000,

APG II 2002,

Judd et al. 2002Slide40

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)Slide41

Basal Angiosperms:

Amborellaceae (Amborella Family)

Amborella trichopodaSlide42

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!!