EVOLUTION OF PLANTS
John C. Studenroth
SETTING THE PARAMETERS
What do we mean when we speak of
"plants" or "algae?
These terms span four of the five
kingdoms of living things!
KINGDOM MONERA: prokaryotes
Bacteria: includes photosynthetic &
Cyanobacteria: formerly called "bluegreen algae'
KINGDOM PROTISTA: unicellular eukaryotes
Protozoa: includes some photosynthetic
types, even though "animal-like"
important in zooplankton
Algal protists: e.g., unicellular algae
important in phytoplankton
KINGDOM FUNGI: very diverse group of eukaryotic heterotrophs
important as symbionts, e.g., lichens,
KINGDOM PLANTAE: multicellular eukaryotic autotrophs
The "higher algae" or "lower plants"
Division Chlorophyta: green algae,
about 7,000 species
Division Phaeophyta: brown algae, about 1,500
Division Rhodophyta: red algae, about 4,000 species
nonvascular land plants: some 23,600 species
mosses, liverworts, hornworts
The vascular land plants:
Lower (seedless) vascular plants, about
mosses, horsetails, ferns
Gymnosperms, about 720 species
conifers, cycads, Ginkgo
Angiosperms, about 275,000 species!
flowering & fruiting plants,
both monocots & dicots
about 6x the number of species of all other
plant groups combined!
SCANNING THE FOSSILS
What has a century of paleobotany told
us about the appearance of these
four kingdoms over time?
PRECAMBRIAN ERA: 3.8 to 0.6 billion years ago
Evidence of first bacterial cells about
3.5 b.y. ago (MONERA)
of first cyanobacteria about 2.8 b.y. ago (MONERA)
Evidence of first
eukaryotes about 1.45 b.y. ago (PROTISTA)
Evidence of primitive fungi
PALEOZOIC ERA: 600 to 225 million years ago
CAMBRIAN PERIOD: 600 to 500 millon
algae dominant (PROTISTA)
ORDOVICIAN PERIOD: 500 to 430 million
marine algae dominant
some modern groups of algae and fungi
first land plants (?) in Upper
SILURIAN PERIOD: 430 to 395 million years ago
tracheids found in as yet unidentified sterile stems
Division Rhyniophyta, ancestors to our Division Tracheophyta
DEVONIAN PERIOD: 395 to 345 million years ago
major diversification of
vascular plants in Lower Devonian Division
ancestors to our Class Lycopsida?
Division Trimerophyta, ancestors to
the "progymnosperms and to our
Classes Filicopsida (ferns) and
and microphyllous leaves in Lower Devonian
evidence of secondary growth
in Middle Devonian
arborescence, seeds, progymnosperms, and
megaphyllous leaves in Upper Devonian
CARBONIFEROUS PERIOD: 345 to 280 million years ago
(Lycopsida) and horsetails (Sphenopsida) dominant in the
Lower Carboniferous (Mississippian) 345
to 320 my. ago
forests of ferns
(Filicopsida) and socalled 'seed ferns (actually gymnosperms,
extinct order Pteridospermales) in the
Upper Carboniferous (Pennsylvanian) 320 to 280 my. ago
many bizarre forms
that are now extinct
PERMIAN PERIOD: 280 to 225 million years ago
first conifers, cycads,
a time of major extinctions
MESOZOIC ERA: 225 to 65 million years
TRIASSIC PERIOD: 225 to 195 million
forests of gymnosperms
and ferns dominate
(e.g., conifers, cycads, Ginkgos, etc.)
JURASSIC PERIOD: 195 to 135 million years ago
similar to Triassic
(ferns, cycads, etc.)
CRETACEOUS PERIOD: 135 to 65 million years ago
another time of major extinctions
CENOZOIC ERA: 65 million years ago to
TERTIARY PERIOD: 65 to 2.5 million
rise of monocotyledons
QUATERNARY PERIOD: 2.5 million years
ago to present
extinction of many
decline of woody plants
rise of herbaceous plants
SOME PUTATIVE SCENARIOS
How does it all fit together?
SOME MAJOR PROBLEMS
For all macroevolutionary schemes
Origin of eukaryotes
Origin of angiosperms
Frequent invoking of
A few problems for all varieties of creationists, too!
Several major extinctions - what was
The biggest jump of all
Our ongoing knowledge explosion
Indirect evidence for cyanobacteria (i.e., stromatolites) from 3.5
billion years ago,
yet these organisms were doing "modern"
THE "HATCH-SLACK" OR FOUR-CARBON PATHWAY
A smaller jump, but too big for us to
emulate with random mutations
MICROEVOLUTION AMONG PLANTS
A quick look at some striking examples
Just how far does microevolution go in the botanical world?
Andrews, Henry N. 1980. The Fossil Hunters: In Search of Ancient
Ithaca: Cornell University Press.
- history of paleobotany with
Andrews, Henry N. 1961. Studies in Paleobotany.
New York: John Wiley and Sons.
- a good introductory textbook of
Arnold, Chester A. 1947. An Introduction to Paleobotany.
New York: McGraw-Hill. ]
- cited several times by Anderson &
in Fossils in Focus; for many years the standard college textbook.
Banks, Harlan Parker. 1970. Evolution and Plants of the Past.
CA: Wadsworth Publishing Co.
- a nifty little paperback, part of the
"Fundamentals of Botany" series.
Barrett, Spencer C.H. 1987. "Mimicry in plants." Scientific American
Beck, Charles B., ed. 1976. Origin and Early Evolution of Angiosperms.
New York: Columbia University Press.
Chaloner, W.G., A.J. Hill, and W.S. Lacey. 1977. "First Devonian
platyspermic seed and its implications in gymnosperm evolution." Nature
Edwards, D. and E.C.W. Davies. 1976. "Oldest recorded 'in situ'
tracheids." Nature 263:494495.
Gensel, Patricia G. and Henry N. Andrews. 1987. "The evolution of early
land plants." American Scientist 75:478-489.
- since land plants appear
1.5 billion years after first algae, transition to land is seen as
extremely difficult, yet "convergent" adaptations to life on land
occurred independently in several plant groups.
Gensel, Patricia G. and Henry N. Andrews. 1984. Plant Life in the
Westport, CT: Praeger.
Gillespie, William H., Gar W. Rothwell, and Stephen E. Scheckler. 1981.
"The earliest seeds.' Nature 293:462-464.
Graham, Linda E. 1985. 'The origin of the life cycle of land plants."
American Scientist 73:178186.
- suggests a simple modification of the
life cycle of an extinct green alga as the likely origin of the first
Gray, J. 1985. 'The microfossil record of early land plants: Advances
in understanding early terrestrial ization, 1970-1984." Phil. Trans.
Royal Soc. London B309:167-195.
- argues from microfossil assemblages
of spores in late Ordovician Period that early phases of terrestrial
plant life mav have occurred this far back.
Harborne, J.B., ed. 1970. Phytochemical Phylogeny.
New York: Academic Press.
Meyen, Sergei V. 1987. Fundamentals of Paleobotany. Chapman and Hall.
Pickett-Heaps, Jeremy. 1982. New Light on the Green Algae. Carolina
Biology Reader #115.
Burlington, NC: Carolina Biological
Pickett-Heaps, Jeremy and H.J. Marchant. 1972. 'The phylogeny of the
green algae: a new proposal." Cytobios 6:255-264.
Stubblefield, Sara P., T.N. Taylor, and James M. Trappe. 1987. "Fossil
mycorrhizae: a case for symbiosis." Science 237:59-60.
- one of
barriers to survival on dry land initially would be lack of soil (of
which a key component is decayed plant matter!); provides evidence for
a conjectured symbiotic relationship between roots of early vascular
plants and fungi.
Tschudy, Robert H. and Richard A. Scott. 1969. Aspects of Palynology.
New York: Wileylnterscience.
- palynology = pollen analysis,
reconstructing ancient floras based on observations on pollen grains
and spores in ancient peat and sedimentary deposits. The resistance to
decay of the outer coats of pollen grains, plus their distinctive
sculpturing makes possible both qualitative and quantitative estimates
of species occurring thousands of years ago.
Vidal, Gonzalo. 1984. 'The oldest eukaryotic cells." Scientific