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2/23/11
2/23/11
What is a land plant?
Embryophytes
Any photosynthetic eukaryote that can survive and sexually reproduce on
land
All land plants are embryophytes (= embryo bearing plants)
•  Defined by a true alternation of generations with multicellular diploid
and haploid phases, and the two phases remain physically
connected.
Notes available from website
• 
• 
Diversity and evolution of major groups of land plants
Gametophyte (haploid) stage
Sporophyte produces
sporangia which make
haploid spores
Gametophyte produces haploid
gametes, which unite in the
archegonium of the gametophyte
Sporophyte (diploid) stage
Robin Allaby
(http://www2.warwick.ac.uk/fac/sci/whri/research/archaeobotany/)
A brief history of time
Notes available from website
Overview
Evidence of first land plants: 480-360 Mya
•  cuticles & stomata
•  archegonium & sporopollenin walled spores
•  vascular systems
•  Origin of land plants
•  Evolutionary history of land plants
–  Major morphological innovations:
alternation of generations
cuticles and stomata
vascular tissues
heterospory
seeds
leaves
flowers
•  Resultant phylogenetic tree of plants
•  Some evolutionary trends
convergence
polyploidy
genome expansion
(417)
(440)
1 cm bar
545
495
Cambrian
Ordovician
• 
417
Silurian
354
Devonian
292
Carboniferous
251
Permian
202
Triassic
Jurassic
142
65
Cretaceous
24
Palaeogene
458
1.8
Neogene
Q
Vascular tissues: evolution of xylem and phloem
What is a land plant?
Invasion of land was really an invasion of the air
•  dessication and support are the principal problems
•  adaptation to dessication requires :
a cuticle (and consequentially stomata)
spores and seeds (ultimately)
vascular tissue (when plants are above a certain size)
440
(495)
Circa 415 Mya Cooksonia paranensis (Gerrienne et al 2006)
Heterospory
embryophytes
Any photosynthetic eukaryote that can survive and sexually reproduce on
land
better adapted for moist
environments than
tracheophytes
amplification of
gametophyte
poikilohydric
amplification of
one stage must
reduce the other
better adapted for dry
environments than
bryophytes
unisexual
gametophytes,
manifest as
heterosporous
amplification of
sporophyte
397 - 391 Mya
(Eifelian)
homoihydric
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non vascular
vascular
(bryophytes)
(tracheophytes)
mosses,
liverworts and
hornworts
ferns, lycopods,
horsetails, and
seed plants
See Proctor 2007
phyletic trend for taller
sporophytes, bisexual
gametophytes,
homosporous
plants that release spores = pteridophytes (fern like - includes lycopods (L), Horsetails (H)
and Ferns (F))
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Heterospory
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Heterospory
The late arrival of leaves: 360 Mya!! (end of
Devonian)
Pollen tubes by early Carboniferous
•  Seems odd - reduces the chances of fertilization by separating
egg and sperm. Cannot be good in a harsh environment, this is
a cost.
•  Once separated, makes sense to increase energy investment in
the “female” gametophyte which must support the sporophyte,
and maximize chances of successful fertilization by making
male spore numerous, (and consequently small).
•  Gives rise to out-crossing. Perhaps this is the advantage (?).
•  That it is an advantage is proven by the convergence on the
habit - possibly as many as 11 times! (Bateman & DiMichele
1994).
homospory
heterospory
Leaf evolution associated with falling CO2 levels (first plants evolved in a CO2 rich
atmosphere)
(Rothwell 1972)
The logical progression of heterospory
e.g. Barinophyton citrulliforme
e.g. Chaleuria cirrosa
e.g. Cystosporites devonicus
Seed habit - the next step after heterospory
(Beerling 2005)
A snapshot of the Carboniferous
•  retain megaspore in megasporangium
•  reduce functional megaspores to 1
•  retain megagametophyte (elimating requirement for external water
for fertilization)
•  modification of megasporangia to receive microspores
•  modification of microspores to enable them to deliver sperm cells to
eggs (ie pollen tube)
•  integument develops around megasporangia (later)
Lycopod trees
(Lepidodendron)
Angiosperms appear 144 Mya (early Cretaceous)
Equisetoid trees
(Calamites)
e.g. Archaeopteris & Selaginella
increasing investment in
megaspore causes
reduction in megaspore
number
all seed plants = spermatophytes
first seed plants = gymnosperms (naked seeds)
Asteropollis sp. Pollen (Laurales) (Friis et al 2005)
Oldest seed plant 385 Mya (Mid Devonian)
Basic Gymnosperm architecture
Evolution of Angiosperms
Explosion in Angiosperm speciesGnetales is
gymnosperm group closest to flowering plants
salpinx
•  Angio = container - megasporangium (and integuments) enclosed
in carpel.
•  Flower structure (a determinate shoot built from leaves).
•  2 integuments not one (as in gymnosperms).
•  Double fertilization (resulting in triploid endosperm).
•  Xylem structure (vessel members and sieve tubes).
•  Other features to such as endopolyploidy ability (weed technology!),
vegetative reproductive ability (weed technology!).
•  Very versatile - numerous floral strategies possible - a single
mutation can result in sexual isolation and new species formation.
•  Introduction of animal based pollination strategies.
integument +
megasporangium
uncovered
megasporangium
Angiosperms
220 000 species
Bryophytes
22 400 species
Pteridophytes
9 000 species
Gymnosperms
750 species
Fabaceae alone have 14000 species
Also only land plant group to reinvade
the sea (Zostera sp.)
Integument does not
fully enclose ovule
Runcaria heinzelinii (Gerrienne et al 2004)
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The diversification of angiosperms: Darwin’s
abominable mystery
Oldest flower fossils circa 125 Mya.
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Evolutionary Trends: convergence (on tree habit)
Evolutionary Trends: convergence (on cactus habit)
Evolutionary trends: polyploidy
Evolutionary trends: genome obesity
•  The rapid appearance of so many species of angiosperm was a
problem for Darwin’s theory
•  In his version of events, evolution proceeds gradually, selecting
minute changes
•  Saltation was an opposing view point – gives more emphasis to
mutation (internally driven) than Natural Selection (externally
driven)
•  Darwin discovered the reason, and founded ‘pollination biology’
Water lily (Nymphaeales) (Friis et al 2001)
Angiosperms diversified because of floral
morphology and pollinator co-evolution
Floral evolution – protection to attraction
Bisexual flowers
Nectar reward, bees, predominate
birds, moths, bats
wind pollination
First pollinators:
beetles in small
inconspicuous
flowers
Unisexual flowers
predominate
Blanc and Wolfe 2004
Friis et al 2006
basal
buttercups, poppies
grapes
cactus
Docks, rhubarb & sorrels
witch hazel, stone crops
mistletoe
water lillies
pepper (spice)
magnolia
basal complex:
primitive dicots
bay laurel
geraniums
Oldest tricolpate
pollen 120 Mya
basal
core
Obesity in the Liliales
Fritillaria (Liliales) 127 000 Mb
wood sorrel
beans, peas, acacia
Large cells, slow replication - good for
bulbs
roses, apples
cucumber, melons &pumpkins
monocots
Oaks, birch, beech
evening primrose
Cabbages, Arabidopsis
asparagus
Arabidopsis (Brassicales)
157 Mb
cotton, lime trees
Lillies, daffodils etc
oranges, lemons
30 Mya CO2
levels crashed:
C4 metabolism
evolved 62 times
independently!!
26 in monocots
and 36 in eudicots
Angiosperm
Phylogeny basal
yams
dogwood
asterids
heather, rhododendron, primrose
Small cells, fast replication good for weed habit
palms
pineapples/air plants
Endangered species?
rosids
Euphorbia, willow
peace lillies
Based on DNA
sequences such
as rbcL, matK,
nadh, atpB, 18S
rDNA
Leitch et al 2005
Potato, tomoto, deadly nightshade
coffee
Mint, basil, rosemary, thyme etc., olives
reeds and rushes
grasses
ginger, bird of paradise plants
Tricolpate
Angiosperms
Why is there an over-representation of large genomes in the plant Red List?
holly
carrots, parsley. fennel
honeysuckle, elder
daisy, asters, thistles, bellflowers
Vinogradov 2003, but read also Cavalier-Smith 2005
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Suggested reading
Crane PR, Friis EM, Pedersen KR (1995) The origin and early
diversification of angiosperms. Nature 374: 27-33.
Friis EM, Pederson KR, Crane PR (2005) When the earth started
blooming: insights from the fossil record. Current Opinion in Plant
Biology 8:5-12.
Judd WS, Campbell CS, Kellogg EA, Stevens PF (1999). Plant
Systematics: A Phylogenetic Approach. Sinauer Associates, Sunderland,
Massachusetts.
Kenrick P and Crane PR (1997) The origin and early evolution of plants Cavalier-Smith T (2004) Only six kingdoms of life. Proceedings of the
on land. Nature 389:33-39.
Royal Society of London Series B. 271:1251-1262.
Niklas K (1997) The evolutionary biology of plants. University of
Friis EM, Pederson KR, Crane PR (2001) Fossil evidence of water
Chicago Press, Chicago.
lilies (Nymphaeales) in the early cretaceous. Nature 410: 357-360.
Friis et al 2006 Cretaceous angiosperm flowers: Innovation and
evolution in plant reproduction. Palaeogeography,
Palaeoclimatology, Palaeoecology 232 (2006) 251–293
Other source material
Friis et al 2010 Diversity in obscurity: fossil flowers and the early
Bateman RM and DiMichele WA (1994) Heterospory: The most
history of angiosperms. Phil. Trans. R. Soc. B 2010 365, 369-382
iterative key innovation in the evolutionary history of the plant
Gerrienne P, Meyer-Berthaud B, Fairon-Demaret M, Streel M,
kingdom. Biological Reviews of the Cambridge Philosophical Society
Steemans P (2004) Runcaria, a Middle Devonian Seed Plant Precursor.
69:345-417.
Science 306:856-858.
Beerling DJ (2005. Leaf Evolution: Gases, Genes and Geochemistry.
Gerrienne P et al. (2006) An exceptional specimen of the early land
Annals of Botany 96:345-352.
plant Cooksonia paranensis, and a hypothesis on the life cycle of the
Blanc G, Wolfe KH (2004) Widespread paleopolyploidy in mode plant earliest eutracheophytes. Review of Palaeontology and Palynology
species inferred from age distributions of duplicate genes. The Plant
142:123-130.
Cell 16:1667-1678.
Leitch IJ, Soltis DE, Soltis PS, Bennett MD (2005) Evolution of DNA
Cavalier-Smith T (2005) Economy, sped and size matter: evolutionary amounts across land plants (Embryophyta). Annals of Botany
forces driving nuclear genome miniaturization and expansion. Annals
95:207-217.
of Botany 95:147-175.
Proctor M (2007) Ferns, evolution, scale and intellectual impedimenta.
New Phytologist 176:504-506.
Rothwell GW (1972) Evidence of Pollen Tubes in Palaeozoic
Pteridosperms. Science 175:772-774.
Vinogradov AE (2003) Selfish DNA is maladaptive: evidence from the
plant Red List. Trends in Genetics 19:609-614.
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