Flowers and Their Evolution - PowerPoint Presentation

Slide1

Flowers and Their Evolution

Spring

2014Slide2

Flower

= a short, determinate shoot bearing highly

modified leaves, some of which are fertile (i.e.,

bearing either microsporangia or

megasporangia

),

with

the microsporangia in

stamens

and the

megasporangia

in

carpels

.Slide3

Flower

REPRODUCTIVE STRUCTURE – Evolutionary requirement to reproduce by sexual means. Pollen transfer and seed dispersal needed.

MODIFIED FOLIAR APPENDAGES – all function together to form the reproductive organ known as the FLOWER.

MODIFICATIONS OF LEAVES – All floral organs are modified LEAVES.

Four terminal WHORLS of modified leaves:

- Two outermost

whorls (sepals, petals)

are sterile (

non-

meiotic

tissues)

- Two innermost whorls (

sporophylls

) are “fertile” with

tissues capable of undergoing meiosis

SPOROPHYLLS – those modified leaves with meiotic capacity.

-

Microsporophylls

– stamens – produce pollen in anthers

-

Megasporophylls

– carpels – produce eggs in ovulesSlide4

Fig. 6.2 from SimpsonSlide5

Floral Whorls

Attached to RECEPTACLE

Sepals

(collectively the Calyx)

Petals

(collectively the Corolla)

Stamens (anthers + filaments)

collectively the Androecium

(

andros

= male; -

oecium

= house)

“Pistil” – carpel(s) [fused or not

] collectively the Gynoecium

(

gynos

= female; -

oecium

= house

)Slide6

Floral Parts: Major whorls

pistil

(1-many carpels)

-

gynoecium

stamens - androecium

petals - corolla

sepals - calyx

receptacleSlide7

young

leaves

XS of

flower

bud

Sepals and petals are

relatively leaf-like.

sepal

petal

stamen

pistilSlide8

Fig. 6.5 from Simpson

“ABC”

Model of

Floral

developmentSlide9

Floral AnatomySlide10

Evolution of the Androecium

DERIVED FROM MODIFIED LEAVES

- Microsporangia (meiosis

 microspores 

pollen grains) on lamina originally

INCREASING LEVELS OF REDUCTION

- Lamina becomes filament

- Sporangial tissue becomes anther wall

- Provides for release of pollen

CAN

BE IN A SINGLE WHORL OR MULTIPLE WHORLS - Tremendous variation in flowering plants. - Often associated with specific type of pollinator. Slide11

laminar

stamens

Stamen evolution

microsporangiaSlide12

Fig. 9.26

Fig. 9.25Slide13

Floral AnatomySlide14

Evolution of the Carpel

MODIFICATION OF MEGASPOROPHYLL

- Evolution of

megasporophyll

structure traced back to seed ferns – 200 to 300

mybp

LEAF WITH MARGINAL MEIOTIC ZONES FOLDS

- Ovules located at margins of

sporophylls

- Lamina curves inward (toward the floral axis -

adaxially) - Carpel is formed by folding – conduplicate

- Margins fuse, enclosing ovules - Carpel(s) = gynoeciumFUSION OF CARPELS

- Unfused (separate) carpels - apocarpous

- Fused (united) carpels - syncarpous POSITION OF THE GYNOECIUM relative to other floral whorls is important in describing floral structures.

PLACEMENT OF OVULES (placentation) within the gynoecium is also important; shows evolutionary origins of the carpel.Slide15

The Ovule =

integumented megasporangium

integuments

female

gametophyte

(derived

from a single

spore)

sporangium

micropyleSlide16

Carpel evolution

(Ovules)

(

megasporophyll

)Slide17

Folding of

megasporophyll

to form simple carpel

S = suture; formed

by fusion of leaf

margins; receptive

to pollen

Folding of

one

megasporophyll

receptacleSlide18

Carpel evolution

stigmatic

crest

stigmaSlide19

Fig.

9.30 from Simpson

3 pistils

1 pistilSlide20

Simple Carpel –

One PistilSlide21

Apocarpy

– Separate

Carpels = 5 pistils in this exampleSlide22

Apocarpous

gynoecium –

Ranunculus

sp

.

with many pistils

elongated receptacleSlide23

Magnolia

LiriodendronSlide24

Fig. 9.31 from Simpson

Simple vs. compound ovarySlide25

Syncarpous

gynoecium – One pistil, 3 carpelsSlide26

Various gynoecia –

Apocarpous

vs.

Syncarpous

(Hint: stigma number usually = carpel number)Slide27

Syncarpy

–

How many carpels?

Locules

?Slide28

Adnation

: Fusion of different

whorls

Stamens (filaments)

adnate

to

petals,

petals

adnate

to sepalsSlide29

Connation: Fusion of

parts from the same whorl

Fusion of filaments into a staminal tubeSlide30

Fig. 9.32

from Simpson

Ovary position relative to other parts

The hypanthium (floral cup) requires

b

oth connation and

adnation

.Slide31

Ovary

s

uperior

Citrus

sp.

Parts

hypogynousSlide32

Ovary superior, parts

perigynous

(floral cup or tube = hypanthium present)

Rosa

sp.Slide33

Ovary inferior,

p

arts

epiperigynous

(hypanthium present

)

Fuchsia

sp.Slide34

Ovary

i

nferior,

p

arts

epigynous

Vaccinium

sp.Slide35

Ovules and Placentation

OVULES CONTAIN THE MEGAGAMETOPHYTE

- Provides for fertilization of egg cell in

megagametophyte

and

protection during development.

- Ovule matures into the SEED.

ATTACHMENT OF THE OVULES VIA FUNICULUS

- Analogous to the mammalian “umbilical cord”

- Point of attachment on inner ovary wall is the PLACENTA

- Can vary depending on type of flower. PLACENTATION IS OFTEN DIAGNOSTIC - Plant families typically have one placentation type. - Often best seen with cross section through ovary.

PLACENTATION REFLECTS EVOLUTIONARY DEVELOPMENT - Fusion of carpels, presence of vascular bundles, etc. can support hypotheses about evolution of particular

flower structures.Slide36

Fig. 9.33

f

rom

SimpsonSlide37

Fig. 9.33,

Part A onlySlide38

Axile

Parietal

PlacentationSlide39

Floral Symmetry

Radial

Bilateral

Zygomorphic

ActinomorphicSlide40

Merosity

= basic number of parts

in each whorl

-3 sepals, 3 petals, 6 stamens, 3 carpels = 3-merous

(or

trimerous

)

-4 sepals, 4 petals, 6 or 8 stamens, 2 or 4 carpels =

4-merous (or tetramerous)

-5 sepals, 5 petals, 5 or 10 stamens, 3 or 5 carpels = 5-merous (or

pentamerous)Slide41

Interpretation of Floral Structures

OBSERVE STRUCTURES IN EACH

WHORL

- How many whorls are there?

- How many parts are present in the calyx? Corolla? - Describe the androecium, then the gynoecium.

DETERMINE

POSITION

OF THE

FLOWER PARTS RELATIVE TO THE OVARY

-

Hypogynous? Perigynous? Epigynous? Epiperigynous?GYNOECIUM

- Apocarpous? Syncarpous? If so, how many carpels? - Position? Superior or inferior or half-inferior?

- Placentation? ADNATION or CONNATION? - Fusion of floral parts can sometimes be diagnostic.

UNUSUAL OR REMARKABLE FLORAL STRUCTURES? - Specializations for pollination?