Download - Overview of land plant phylogeny (more detail)

Last Week
-The land plant clade
-The Tracheophytes
-The fossil record
- Overview of land plant phylogeny (more detail)
- 4 central functions all land plants ‘do’
- Importance of physical laws in shaping plant form
Function, and evolution
- hydraulics
Lecture 8
Feb. 6th, 2007
Overview Today
(1)
Cope’s Rule - why is bigger better?
Plant size and plant hydraulics
Basics of plant hydraulics that rely on vascular ‘tubes’
Hagen - Poiseuille equation describes
how selection should govern the evolution
of plant hydraulics
(2)
PaleoBotany
Early split in vascular plant evolution
‘Leaf’ Evolution
Convergent evolution
Several important paleo plants
Each major plant clade has increased in max. size over time
Cope’s Rule (E.D. Cope 1896)
Evolution of Angiosperms
Evolution of Tracheophytes
Fossil record - rapid evolutionary increases in the
size and height of sporophytes
Continued colonization on land required adaptations for
Efficient internal transport
Desiccation resistance or avoidance
Reproduction without water
Effective dispersal
Competition (for multiple resources)
What enabled plants to continue to increase in size?
Two fundamental constraints influencing plant hydraulics
and gas exchange
(1) Increasing cost of resistance with increased height
(2) Photosynthesis/transpiration compromise
First ‘pipe’
The tracheid
Second pipe
- All tracheophytes
The vessel
- Mostly Angiosperms
Tracheid diameter
Throughout the evolution
of the Tracheophytes . . .
. . . with increases in transport distance (size) tracheid
and vessel dimensions have changed
Likely enabled plants
to increase in size
Engineering principles the most direct method is through ‘pipes’
Hagen - Poiseuille equation
8"li
Zi = 4
ri
Resistance of fluid flow = Zi
li
ri
Length of pipe = li
Radius of pipe = ri
η = fluid viscosity
What parameters can selection
act on?
What happens to resistance with changes in
length vs. increases in radius?
8"li
Zi = 4
ri
Resistance decreases linearly
with decreases in length
But it decreases as r-4
Consider the advantage of the evolution of
vessels in angiosperms…
Tracheid diameter
Throughout the evolution
of the Tracheophytes . . .
. . . with increases in transport distance (size) tracheid
and vessel dimensions have changed
Selection to lower
resistance of transport . . .
Likely enabled plants
to increase in size
Flux density of water through plants (Transpiration)
On land . .
Plants require 138.8 moles of water (lost)
per mole of CO2 that has been photosynthetically fixed
BUT AVAILABLE WATER MAY BE LIMITED
Increase transpiration <-> increase photosynthesis
Decrease transpiration <-> decrease photosynthesis
Photosynthesis/Transpiration compromise
Paleo Botany
B
Lycopods Horsetails Ferns
Bryophytes
Gymnosperms Angiosperms
L -> A
Tracheophytes
B
Zosterophyllophyta
Trimerophya
Rhyniophyta
Antheridia and Archegonia
All the ‘action’ happens within the Devonian!
Tall and Diverse Floras by the Carboniferous
Early Vascular Plants
The Evolution of the Leaf
•Leaves essentially govern terrestrial biogeochemical and
Ecological processes.
•Early land plants and vascular plants had photosynthetic
stems with low stomate densities
•‘Megaphyll leaves’ appeared ~ 360mya (end of Devonian)
about 40my after the first land plants
•These ‘Megaphyll leaves’ characterized by
greater stomate densities
•Greater densities of stomates = greater transpiration
rates (water use) = greater carbon flux
•Evolution of the leaf corresponds with dramatic drop
in atmospheric CO2
‘Leaves’ - are not all the same!
Three analogous structures
(1) ‘Leaves’ on gametophytes of nonvascular plants
(2) Enations/microphylls of Zosterophyllophytes
and Lycophyta
Vascular system grows into Enation
after development of ‘leaf-like’ extension
(3) Megaphylls - true leaves that evolved from
branch systems. Present in all seed plants
Leaf develops with vascular system
during development
Two distinct lines of Land Plant Evolution
Evolutionary Split in Vascular Plant Evolution
(2)
Megaphyll
(1)
Microphyll
Remember
that early
split we talked
about??
Extant Lycopods
Sporangia
Clubmosses
All you see is Sporophyte!
Within both lines many examples of
convergent evolution
Traits similar to seed like plants evolved
independently with the Microphyll line!
What does convergent evolution suggest?
(1) Microphyll line of evolution
A distinct line of evolution from seed plants
Gave rise to the Lycophyta (Lycopods)
Share common ancestor with Zosterophyllophyta
Enations (leaf-like extensions)
Increased photosynthetic surface areas
Enations = Microphylls
Not the same as leaves but functionally similar!
Reached up to 78cm long (!)
Microphyll Line of Evolution
Not all leaves are the same!
Enations (‘leaf-like’ extensions)
(1) Independent evolution of leaf-like structures
Microphyll Line of Evolution
(2) Independent evolution of true roots
(3) Independent evolution of vascular cambium
and secondary growth
But - vascular cambium could not undergo
radial longnitudinal division
Cambial cells became increasingly wider!
No specimen larger than 10cm thick
Microphyll Line of Evolution
(4) Independent evolution of Heterospory
(5?) Megaspore in some species retained within sporophyll
Similar to ovules and seeds in seed plants
-BUT Sperm still needed to swim
(6) Tree-like habit
Convergent evolution within the Lycophytes
-‘Leaves’
- Roots
-Secondary growth
-Heterospory
-‘Proto’ ovules/seeds
-Tree-like habit
(2)
(1)
Lycophytes dominated in the
Devonian and Carboniferous
-Comprised 2/3 of all plants within the Carboniferous
-Common in swampy areas (restricted to wet environs!)
But there are only 5 genera living today
Lycopodium (club moss)
Extinct Lycophytes
Leaves = microphylls
Lepidodendron
Sporangia within cones (strobili)
Strobili - reproductive structures
which contain a high concentration
of sporangia.
Sigillaria
Monopodial growth
Sigillaria
Lepidodendron fossils
“Enations”
www.twoguysfossils.com/ plants_usa.htm
Early Carboniferous Forests
(2) Megaphyll line of plant evolution
The first plant with ‘true’ leaves (megaphylls)
~ 6m tall!
Archaeopteris fissilis from the archive
kept by Prof. E.M. Friis at the Stockholm
Museum of Natural History
True leaves first became widespread with the
appearance of the genus Archaeopteris,
the first forest tree, and typical of the Late
Devonian period approximately 360-375 Myr ago.
Archaeopteris fissilis had small, dissected leaves
http://www.palaeobiology.org.uk/projects_01.htm
(2) Megaphyll line of
evolution
Trimerophyta Mya ~370 - 380
Pteridophyta (Ferns)
(2)
--> spores
(1)
Two early evolutionary
lines with the Megaphylls!
Early seed plants(5-6 distinct groups)
Progymnosperms (extinct)
Mya ~363
Pteridosperma - ‘seed ferns’ (extinct)
Cordaitles Similar to extant gymnosperms
Seeds in ‘Cone’ like structures
300 mya Late Carboniferous
Early seed plants
Progymnosperms
Apical dominance
growth form
‘Seed Ferns’
Pteridosperma
LEAVES bear ovules -> seeds
Horrible Name! Don’t be
confused - these are not
Pteridophytes (ferns)
Carboniferous plants
363-290mya
Swamp, moist forests
Dominated by 5 major plant groups
Lycophytes
Club mosses (extant - barely!!!)
Spenophytes Horesetails (extant)
Pteridophytes Ferns (extant)
Progymnosperms (extinct)
Early Seed Plants (many extinct)
Carboniferous forest . . . .
Wet - swamp forests
First animals - insects, early reptiles
“Today . . . . Fossil Fuel”
(2) Megaphyll line of evolution continued . . .
Descendents of progymnosperms (Cordaitles) gave rise to
Gymnosperms with two more major evolutionary lines
An evolutionary line which gave rise to
Cycads
Ginko
Swimming sperm!
Elements of a ‘pollen tube’
Another evolutionary line gave rise to
Conifers
Gnetophytes
Sperm non-mobile
Pollen tube
Flowering Plants
Carried to egg by growth of
microgametophyte as a pollen
tube (elaborate)
Spermatophytes
Evolution of the Seed
Questions
•What does the Hagen-Poiseuille equation tell us about
plant evolution?
•What is Cope’s Rule?
•Name as many cases of convergent evolution in the
microphyll line as you can
•What does convergent evolution tell us about plant
evolution and how plants work?
•Compare the microphyll line of evolution with megaphyll line
•Lepidodendron?
•What is the photosynthesis/transpiration compromise?