lecture9 2006 handout - botanical information and ecology...

The Angiosperms

The Angiosperms

Angiosperm diversity & dominance

Key innovations

Evolutionary trends

Angiosperm phylogeny (part I)

What are Angiosperms?

Flowering Plants!

Gymnosperm

= “naked seed”

Angiosperm

=“hidden seed”

ovules (seeds)

carpel (ovary)

15,000Mosses

1250Lycopods

257,000Angiosperms

820Gymnosperms

12,500Ferns

9000Liverworts

Diversity of angiosperm species...

Diversity of...

growth form

environments

pollination

dispersal

biotic interactions

Dominance...

Angiosperm cover most of the earth!

Why are Angiosperms so diverse

and dominant?

Key evolutionary innovations

1. Vessels

2. Double fertilization

3. Carpel

4. Fruit

5. Flower

Vessel elements

Tracheids

Vessels

Function

• rapid conduction of fluids

Consequences

• rapid growth

• but: more susceptible to freezing damage

Lianas

• exceptionally large vessels

• rapid growth

• up to 1/4 of

species in some tropical forests

Drimys (Winteraceae)

Where are vessels disadvantageous?

Tropical high mountains

• secondary loss of vessels

Cold temperate forests

• mostly gymnosperms

• no lianas

Angiosperm megagametophyte

• 8 nuclei

• only egg cell and central cell will develop

• other cells degenerate

Central cell formed from fusion of polar nuclei

Ovule(the whole thing)

Double fertilization

. . .gives rises to embryo & endosperm

becomes

Endosperm

becomes

Embryo

Wheat grain (seed)

Endosperm• = starchy interior of seed• triploid (3n)• formed from fusion of second sperm nucleus (1n)

of microgametophyte and central cell (2n) of megagametophyte

• nourishes developing embryo

Double fertilization

Function

• Results in endosperm

• Endosperm provides food for initial growth of seedling

Consequences

• Faster germination and growth of

seedling

• Increased survival

ovules

carpel (ovary)

= 1 or more CARPELS

POLLEN TUBE

POLLEN

Evolution of the carpel

leaf-like, separate

enclosed, with fusion of

multiple

carpels

Archaefructus• early Cretaceous, ~140 mya\

• leaf-like reproductive structures

show “folded leaf” origin of carpel

1 mm

carpels

Illicium

(Star Anise)

One ovary with 2 fused carpels

One ovary with 5 fused carpels

Ovary = 1 or more fused carpels

Examples of separate carpels

Paeony Strawberry

Examples of fused carpels

Tomato

Mallow

Moneses

The Carpel

Function• Control access by pollen to

embryo

• Protect developing ovules • Provide package for dispersal

(=fruit)

Consequences

• Promote outcrossing• Increased survivorship of seeds

(on and off maternal plant)

= Mature seeds + ovary (or ovaries), along with any accessory tissues

The Fruit

Fruits from a single flower

Flower of three fused carpels

Fruits from

many flowers

Fig

many flowers

...on the inside!

The Fruit

Function• protect seeds• packaging for seeds (sometimes in

large quantities)• attract dispersers

Consequences• prevent seed predation• efficient dispersal to favorable sites

for growth and germination• higher survivorship• isolated populations with large

ranges

COROLLA

(all petals)

CALYX

(all sepals)

The parts of a flower

= 1 or more CARPELS

STAMEN

PERIANTH

POLLEN TUBE

POLLEN

Specialized Pollination

Pseudocopulation(Chiloglottis orchid, thynnine wasp)

Foot-long nectar spur of Angraecum sesquipedale(orchid)

The Flower

Function

• attract pollinators

• assist in pollen transfer

• restrict access by non-pollinators

Consequences

• efficient, controlled pollen transfer

• increased potential for out-crossing

• increased potential for reproductive isolation

• increased speciation

The Angiosperms

Angiosperm diversity & dominance

Key innovations

Evolutionary trends

Angiosperm phylogeny (part I)

Evolution of the carpel

leaf-like, separate

enclosed, with fusion of

multiple

carpels

Evolution of the stamen

leaf-likeclearly differentiated into specialized

filament and anthers

Evolution of the

Angiosperm flower

• Carpels: many, separate

to few, fused

• Perianth parts: all alike,

to clearly differentiated

sepals and petals

• Petals: many, free to

few, fused

• Ovary: superior to

inferior

Floral reduction and fusion

General evolutionary trends

• Fusion

• Reduction

• Differentiation (of form and function)

AN

ITA

gra

de

Mag

noliid

s

Monocots

basal

eudic

ots

Rosids Asterids

Cary

ophyl

lale

s

Angiosperm

phylogeny

the simplified version!

Eudicots

AN

ITA

gra

de

Mag

noliid

s

Monocots

basal

eudic

ots

Rosids Asterids

Cary

ophyl

lale

s

Eudicots

The “ANITA grade”

The “ANITA” grade

rest of the angiospermsA

mbore

lla

Nym

pheale

s

(wate

r lilies)

3 o

ther

fam

ilie

s

The “ANITA” grade

A - Amborellales

N - Nymphaeales

I - Illiciaceae

T - Trimeniaceae

A - Austrobaileyaceae

The “ANITA” families

•Trees and shrub, also floating aquatic plants

•Floral parts spirally-arranged, often numerous, irregular in number

•Perianth parts poorly differentiated into sepals and petals, if at all

•Carpels separate, leaf-like

•Stamens leaf-like

•Vessels absent in some

AmborellaAmborellaceae•shrub of New Caledonia

•no vessels

Nymphaeaceae (water lilies)

AN

ITA

gra

de

Mag

noliid

s

Monocots

basal

eudic

ots

Rosids Asterids

Cary

ophyl

lale

s

EudicotsMagnoliids

•Mostly trees and shrubs

•1000s of species, mostly tropical

•Carpels separate, numerous or in 3s

•Perianth poorly differentiated, parts mostly in 3s

Magnoliaceae

•Numerous, spiralled stamens and carpels

•Perianth parts apparently spiral � actually multiple groups of 3

Other Magnoliid families

Myristicaceae (nutmeg family)Lauraceae (avocado family)

Winteraceae PiperaceaeAnnonaceae

Magnoliid fruits

Myristicaceae (nutmeg family) Lauraceae (avocado family)

Drimys

(Winteraceae) MagnoliaAnnonaceae

multi-carpellate, or reduced to single carpel

AN

ITA

gra

de

Chlo

ranth

ales

Mag

noliid

s

Monocots

Rosids Asterids

Eudicots

The Monocots

basal

eudic

ots

Monocots

• flower parts in 3s• ovary of 3 fused carpels

• 1 cotyledon (first leaf)

• parallel leaf veins• mostly herbs

• scattered vascular bundles • lack true secondary growth

Monocot ovary

Monocots

• flower parts in 3s• ovary of 3 fused carpels

• 1 cotyledon (first leaf)

• parallel leaf veins• mostly herbs

• scattered vascular bundles• lack true secondary growth

Monocot

non-Monocot

Monocot leaf is homologous with petiole of

other angiosperm leaves

leaf blade

petiole

non-monocot leaf

hypothesized evolution of monocot leaf

?

Typical monocot flowers:

• Perianth in 3s

–3 sepals + 3 petals, or 6 all alike

• Six stamens

• Ovary of 3 fused carpelsLiliaceae

Amaryllidaceae

Poaceae (grasses)

Sugar cane

•economically most important plant family: wheat, barley, rice, corn, etc.

•flowers highly reduced, adapted

to wind pollination

Grass spikes: each contains several spikelets

(flowers)

Arecaceae (palms)

individual flowers•note parts in 3s

•Tree-like habit without true secondary

growth

•fibers elongate from single terminal

meristem

Orchidaceae3 sepals

2 petals

lip (modified

3rd petal)

• 1st or 2nd largest family

(25-30,000 species)

• most tropical epiphytes

• extremely specialized

pollination

Questions

1. Name the parts of the flower

2. What are the main synapomorphies of Angiosperms?

3. Which of these traits might have favored the dominance(abundance and biomass) of Angiosperms over much of the earth? Where are Angiosperms not the dominant group of land plants? Why?

4. Which of these traits might have favored the evolution of so many species of Angiosperms? How?

5. Summarize the differences among the ANITA grade, Magnoliids, and Monocots in terms of number, fusion, and arrangement of reproductive parts