lecture9 2006 handout - botanical information and ecology...
TRANSCRIPT
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