John C. Studenroth


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 & chemosynthetic types
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, mycorrhizae

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 species
Division Rhodophyta: red algae, about 4,000 species
The nonvascular land plants: some 23,600 species
Division Bryophyta: mosses, liverworts, hornworts

The vascular land plants:
Division Tracheophyta:
Lower (seedless) vascular plants, about 13,240 species
e.g., club mosses, horsetails, ferns
Gymnosperms, about 720 species
e.g., 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!


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)
Evidence 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 (FUNGI)

PALEOZOIC ERA: 600 to 225 million years ago

CAMBRIAN PERIOD: 600 to 500 millon years ago
algae dominant (PROTISTA)

ORDOVICIAN PERIOD: 500 to 430 million years ago
marine algae dominant
some modern groups of algae and fungi
first land plants (?) in Upper Ordovician (PLANTAE)

SILURIAN PERIOD: 430 to 395 million years ago
algae dominant
vascular plants appear
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
Zosterophyllophyta, ancestors to our Class Lycopsida?
Division Trimerophyta, ancestors to the "progymnosperms and to our
Classes Filicopsida (ferns) and Sphenopsida (horsetails)?
heterospory 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
club mosses (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, Ginkgos
a time of major extinctions

MESOZOIC ERA: 225 to 65 million years ago

TRIASSIC PERIOD: 225 to 195 million years ago
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
angiosperms originate and spread
gymnosperms decline
another time of major extinctions

CENOZOIC ERA: 65 million years ago to present

TERTIARY PERIOD: 65 to 2.5 million years ago
rise of monocotyledons
grasslands develop
forests decline

QUATERNARY PERIOD: 2.5 million years ago to present
extinction of many species
decline of woody plants
rise of herbaceous plants
many desert forms appear


How does it all fit together?


For all macroevolutionary schemes
Origin of eukaryotes
Origin of angiosperms
Frequent invoking of convergent evolution'

A few problems for all varieties of creationists, too!
Several major extinctions - what was God doing?


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" photosyntehsis!


A smaller jump, but too big for us to emulate with random mutations


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 Plants.
Ithaca: Cornell University Press.
- history of paleobotany with biographic emphasis.

Andrews, Henry N. 1961. Studies in Paleobotany.
New York: John Wiley and Sons.
- a good introductory textbook of paleobotany.

Arnold, Chester A. 1947. An Introduction to Paleobotany.
New York: McGraw-Hill. ]
- cited several times by Anderson & Coffin in Fossils in Focus; for many years the standard college textbook.

Banks, Harlan Parker. 1970. Evolution and Plants of the Past.
Belmont, 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 257(3): 76-83.

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 265:233-235.

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 Devonian.
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 land plants.

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 Supply Co.

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 American 250(2):48-57.