|
************************************************************
***************************
How Did the Orchids Get That Way?
March Meeting Recap, Part One - by SEAN EATON
r. Warren H. Wagner, professor emeritus of the U. of M. Department of Botany discussed
the development of orchid complexity and many of the features unique to orchids. The
systematic study of orchids goes back at least to the time of Darwin, and there have been
several theories of how and why they take such diverse forms today. Dr. Wagner began his talk
by outlining how the evolution of plant structures is studied and described generally, then went
on to enumerate a number of interesting characteristics of orchids.
Homology is a term used by those who study the evolution of life forms, essentially an
examination of similarities, gross and fine, that indicate the underlying similarities among living
things. It is the basis for understanding the evolutionary relationships among living things. In
particular, groups of different plants can evolve a similar single feature, (parallelism), or develop
a whole set of set of similar features, depending on habitat. Over time, continual modification
and refinement of the plant forms suggest evolutionary sequences and relationships.
Dr. Wagner described six ways in which the parts of individual flowers progress from lesser to
greater elaboration, and gave examples of familiar plants to illustrate these continua of changes.
The number of flower parts can be indefinite, as in magnolias and water lilies to definite, (that
is a specific number always) in more advanced plants. Individual flower parts can be more or
less undifferentiated from each other, or highly specialized and distinctive, (ie, easily identified
as sepals, stamens, pistils and so on). Flower parts can be reduced in size or in number of
different kinds of flower parts. Certain parts of the plant or flower can be amplified, perhaps to
serve some functional purpose, as with the thorns of a cactus. Flower parts can be elaborated,
as in the columbine, ("a glorified buttercup"). Finally, flower parts can be fused together, as they
are in orchids. Broadly speaking, these are the changes observed in flowering plants.
It is believed that there are approximately 275 thousand different flowering plants. There are
still many gaps in our knowledge of them, and to understand something of their tremendous
diversity we need more botanists who specialize in entire organisms, (as opposed to those who
focus on the microscopic or molecular level). Especially critical is our gap in knowledge of the
tropical orchids, especially given the rapid development of rainforest areas of the world.
Orchids show all of the types of elaboration and differentiation of flower form described above,
so much so that they are clearly "out in left field" relative to other flowering plants. It is
suspected that, in terms of evolution, orchids are closest to lilies and irises, developing over time
from simpler, less elaborate "monocots", a group to which grasses, palm trees and other similar
plants belong. With around 30 thousand species, orchids form the largest family of plants,
(though they may be rare in locales). Orchid flowers range from the beautiful to the weird,
from barely 1 millimeter in size to 16 inches across.
Why are orchids such a large and successful group of plants? Probably the answer lies in their
tremendous diversity of form and adaptation. Dr. Wagner went into considerable detail about
the structures and functions of the different parts of a typical orchid plant. This will be covered
in "part two"of the March Meeting Summary.
************************************************************
|