THE PLANT KINGDOMS
A basic knowledge of plant classification is necessary for understanding the relationships that exist between morphology and anatomy. When classification schemes were first developed, all living organisms
could easily be placed in a general category, like Kingdom Plantae or Kingdom
Animalia.
General categories, such as Kingdoms
still work well in classification but they break down
when some organisms in one category have characteristics which are similar to organisms in another category. A case in point is
the one-celled organism, Euglena, which bears both animal and plant
characteristics.
The establishment of a third Kingdom, proposed by J. Hogg and Ernst
Haeckel around 1860, which contained organisms that did not
develop complex tissues somewhat solved this
problem. The kingdom which was called Protoctista, or Protista, describes a
heterogeneous variety of organisms including algae, fungi, and sponges.
A better but not perfect solution was proposed some 50 years later, when Copeland assigned
the name Monera to all single celled organisms with prokaryotic cells
and the remaining organisms with eukaryotic cells were placed in the
Kingdom Protoctista.
Copeland's four kingdom system of classification was considered to be
a definite improvement but his system did not recognize the character of nutrition which is
a major distinctive element. All differences
in the mode of nutrition among organisms were lumped into
Kingdom Protoctista and this still posed a major classification problem.
In 1969, R. H. Whittaker proposed a five kingdom system which is favored by many biologists. In Whittaker's system, three kingdoms of
more complex organisms are classified according to the three forms of
nutrition: photosynthesis, food ingestion and food absorption. The
other two kingdoms are distinguished on the basis of differences in
cellular structure.
The five-kingdom arrangement still has some problems.
More recently, Woese, a microbiologist, responded to these problems by proposing to
divide the Kingdom Monera into two kingdoms, based on some previously
unrecognized fundamental differences between the major groups of
bacteria.
Much more information still remains to be acquired and until
this occurs, taxonomic categories will remain subject to different
interpretations. In this study, Whittaker's five kingdom system will
be followed.
Note here about the plants selected in this Survey.
Click here to review the Whittaker System.
Here begin the study of Kingdom Monera
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