Transcript ginkgo2 - University of Kentucky

ID 157670
GINKGO TREES ARE LIVING CORDAITES
Donald Chesnut, Retired, University of Kentucky, Lexington, KY 40506-0107 [email protected]
Ginkgo biloba Linnaeus 1771 is the only extant member of the once
flourishing Mesozoic and Tertiary Ginkgophyta group of gymnosperm plants.
Ginkgo trees, now abundant in temperate cities around the world, were thought to
exist in nature only in a small refugium in China. Their dispersal to the rest of the
world by botanists, diplomats and other interested parties began about 300 years
ago. Their natural refugium may no longer exist. During the Mesozoic and
Tertiary the ginkgophytes were cosmopolitan. Early members of the group can be
traced to the Early Permian.
The phylogenetic origin of the enigmatic Ginkgo has puzzled botanists for
the last 150 years. Similarities in wood, reproductive structures and leaf venation
between ginkgophytes and Cordaitales (as well as with cycads) has been noted
for many years. The cosmopolitan Cordaitales existed in the Carboniferous and
Permian periods. They were important constituents of the coal floras of the
Carboniferous, but became extinct before the Mesozoic began.
Leaf venation of both groups is always parallel, branch dichotomously and never anastomose.
Willem Meijer (personal commun., ca 2000) pointed out that cross sections of the leaves of
Ginkgo were identical to those of Cordaites from Carboniferous coal balls.
B. Leaves
Ginkgo
Cordaites-like Ginkgophyte leaves
Cordaites
For simplicity, all parts of the “Cordaites” tree are called Cordaites here.
E. Reproduction
A. Trees
In both cordaites and Ginkgo, the male and female structures are born
on separate cones. Further, in Ginkgo, the male and female cones are on
separate trees (i.e., Ginkgo is dioecious). We do not know if cordaite
cones were on separate trees.
Cordaites
Cordaites principalis,
from Stewart, 1983.
Some types of Cordaites had mangrove-like prop roots. Adventitious
roots have also been noted for Ginkgo.
Baiera, Jurassic, from
Stewart, 1983.
A. Eretmophyllum, Jurassic. B.
Sphenob-aiera, Jurassic, from Taylor
1981.
A, B. Sphenobaiera, Permian-Jurassic. C, D. Arctobaiera. from Stewart, 1983.
Ginkgo biloba, deciduous leaves in winter.
Ginkgo
Cordaites
Ginkgo
C. Branching
.
In both cordaites and Ginkgo, the leaves emerge in a helical pattern.
Ginkgo
Cordaites
Branch with numerous spur shoots. Shoots about 1 cm diameter.
B. Ovules. C. Pollen-bearing organs.
Reconstructions of Cordaites. A. From Scott, 1909. B. From
Cridland, 1964. Note mangrove-like prop roots.
Paired ovules.
Pollen-bearing organs.
Both from General Bio. Supply, in Stewart, 1983.
Cordaites
Ginkgo
Ginkgo at Henry Clay’s estate,
Lexington, Kentucky: circum-ference
3.8 meters at one meter above
ground. Note person
D. Wood
In both cordaites and Ginkgo, the bulk of the wood is secondary wood typical of the
gymnosperms. .
Cordaites
Helically-arranged leaves and
cones, from Stewart, 1983.
Helical leaf scars on spur
shoots. About 1 cm dia.
Two new spur shoots on
old spur shoot.
New branch on old spur shoot.
Ginkgo
A
Dessicated “fruit”
Seed
Cordaites seeds. From Newberry, 1873.
The fleshy “fruit” of the Ginkgo is actually a seed-coat layer and not a
fleshy ovary. Some cordaites may have had fleshy seed coats as well. Some
of the wings may have been compressions of this seed coat.
Pith
B
Thin section of Ginkgo branch. From Catholic
University of Leuven, Belgium.
C
Cordaite pre-pollen
Cordaitina,
Permian,from
Hart in
Tschudy and
Scott, 1969, p.
276.
Florinites, a
mono-saccate
pollen. From
Stewart, 1983.
Florinites,
Carboniferous,
from Kosanke
in Tschudy
and Scott,
1969, p. 248
Ginkgophyte pollen
Cycadopites,
Permian,from
Hart in
Tschudy and
Scott, 1969, p.
278.
A, B, C. Coal-ball peels from
Pennsylvanian of Kentucky.
C. Growth rings in cordaites
wood. All from Phillips and
Chesnut, 1980.
Coal-ball peel from
Pennsylvanian rocks.
P, pith. From Rothwell
in Stewart, 1983.
Conclusions
Ginkgophytes probably evolved from early cordaites in Late Devonian or Carboniferous
times. Ginkgo is here considered to be the only extant member of the Cordaitales much as
birds are considered to be the modern representatives of the Dinosauria. Long, strap-like
leaves, typical in cordaites, are common in tropical, humid environments, whereas small,
compact leaves, as in the modern Ginkgo, are common adaptations to drier, upland
environments. Differences between ginkgophytes and cordaites may be caused by
adaptations to dry-land environments.
Acknowledgements
I am indebted to Dr. Cortland Eble, Kentucky Geological Survey, for his help in
discussions about paleobotany and especially with palynology.
Inspiration for my conclusions derives from discussions with Dr. Willem Meijer
(deceased), University of Kentucky.
The onus of any errors in content, grammar, as well as unfounded conclusions is entirely
mine.
Cycadopites, Ginkgo biloba pollen from
Triassic,from Tschudy in Tschudy and Scott,
Chaloner in
1969, p. 11.
Tschudy and
Scott, 1969, p.
303.
References
Phillips, T.S., and Chesnut, D.R., 1980, Coal balls in lower Middle Pennsylvanian strata of eastern Kentucky:
Occurrences and peat composition [abs]: Geological Society of America, Annual Meeting, Atlanta, Abstracts
with Programs, November 17-20, 1980, v. 11, n. 7, p. 498
Ginkgo and cordaite pollen are monosaccate (one bag).
Ginkgophyte pollen is further characterized as monosulcate
(it has a single furrow). Tschudy (his Table 2-2, p. 15)
placed Cordaitales pre-pollen in the monosulcate category
too (I’m not sure why). Cycadopites probably represent
ginkgophytes, cycadophytes and related groups.
Rendle, Alfred. B., 1904, The Classification of Flowering Plants. University Press, Cambridge University, 403
pp. [Although about flowering plants, this book has an excellent description of the ginkophytes, cycadophytes
and related plants.]
Stewart, Wilson N., 1983, Paleobotany and the Evolution of Plants. Cambridge University Press, 405 pp.
Pith casts (Artisia) of Cordaites.
Section of Ginkgo branch. Showing growth rings in
secondary wood. Diameter 4.5 cm.
Taylor, Thomas N., 1981, Paleobotany, An Introduction to Fossil Plant Biology. McGraw-Hill Book Co., 589
pp.
Tschudy, R.H., and Scott, R.A., 1969, Aspects of Palynology. John Wiley and Sons, 510 pp.