Spring 2014 Flower a short determinate shoot bearing highly modified leaves some of which are fertile ie bearing either microsporangia or megasporangia with the microsporangia in ID: 748139
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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?