Transcript Plant Taxonomy - University of Windsor

Plant Taxonomy
Sometimes also called Systematics, this is the part of botany
that classifies individual plants into groups, usually species,
but also into larger taxonomic groupings.
Historically, until Linnaeus, classification was largely based
on function – medicinal uses – and used the “doctrine of
signatures”
Shape of leaf, colour of sap, form of root was thought
to indicate how a plant might be used. Examples:
Hepatica – the name from ‘liver-shaped’
leaves, and early belief it would be a
good treatment for liver problems
Bloodroot (Sanguinaria) – the roots produce a red sap that
looks like blood, and once believed useful to treat blood
disorders. It is found in eastern Canada (and eastern U.S.), and
is an herbal medicine still (mistakenly) advocated to treat
some cancers.
Mandrake (Mandragora officianarum)
– the root is thought to look like a
human figure. In Harry Potter,
mandrake gave recovery from trances.
In herbal medicine, it was thought to
improve virility and fertility. Actually,
the root contains alkaloids that can
cause hallucinations, unquenchable
thirst, and persistent extreme light
sensitivity.
Dogbane (Apocynum spp.) was considered by herbalists to
increase creativity. However, dogbane has dangerous and
potentially fatal concentrations of cardiac glycosides.
Apparently, it is still used in green teas (in small doses) with
jasmine flowers in Japan and China. In those doses it is said to
lower blood pressure (probably by acting as a diuretic).
The idea of classifying plants with respect to their medicinal
uses was not limited to Western civilization. The idea arose in
Asian civilizations, among aboriginal American tribes and
elsewhere.
Classification remained centered on herbalism through the
Middle Ages and beyond. Division of botany from herbology
only really occurred during the 18th century.
The key figure was Carolus Linneaus. Initially, Linneaus
developed a polynomial (many names) system of classification
in which many descriptive terms were part of the formal name.
He became frustrated. Even he would forget parts of a name.
So, in the key work in plant taxonomy, he started including a
single marginal name next to the complex descriptions. That
became the ‘species’ name in a binomial system.
Species name
Descriptive terms
Linnaeus’ binomials for many European plants, but also a
number from North America, are still used today. In plant
taxonomy, his ‘masterwork’ was Species Plantarum. He also
wrote and slowly modified a more general treatise, Systema
Naturae. As a prof at the University of Uppsala (Sweden), he
had many students who traveled widely and returned
specimens (animals and plants) to him, e.g.
Daniel Solander was the naturalist on James Cook’s round-theworld exploration.
Pehr Kalm spent 3 years in the American colonies collecting
specimens.
Carl Peter Thunberg was the first western naturalist to visit
Japan in more than a century.
Linnaeus also was a trained physician (much of medicine at
the time was herbal) and became personal physician to
Sweden’s royal family. His practice included study and
treatment of STDs.
Late in life he suffered from depression and, after a series of
strokes in 1774, died in 1778.
The Linnaean system of classification is hierarchical. In plant
taxonomy, many of the higher categories have fixed word
endings that identify the level.
An example: the garden Nasturtium (Tropaeolum majus)
There are rules for naming plants. They are determined in the
International Code of Botanical Nomenclature. The rules
apply to the scientific binomial.
Common names are a separate problem. More than one
species may have the same common name (especially across
large areas), and a single species may have different common
names in different places, e.g.:
Andropogon gerardii
-
big bluestem (on the prairies)
turkey foot (locally)
Your text lists 14 different common names for Osage orange
(Maclura pomifera). Some are:
bow-wood
osage apple
hedge apple
hedge osage
horse apple
mock orange
But the last common name is
more commonly applied
to a different group of
flowering shrubs in the genus
Philadelphus
The naming conventions for a binomial only rarely have to
deal with a new genus.
Genus names are usually chosen either as
1. descriptive of the group (e.g. Myriophyllum for its finely
divided leaves; Panicum for its seed head, which is a broad
panicle),
2. Names the person that described it (e.g. Wisteria – for
Caspar Wistar, an important figure in descriptive plant
anatomy)
3. The name is derived from old Latin or Greek words that
described or named the group (e.g. Pinus from the Latin for
pine trees.
Species names can also be:
1. descriptive of characteristics of the plant (e.g. yarrow
(Achillea millefolium) with finely divided leaves that look
like there are thousands)
2. may name the region where it was found (e.g. Solidago
canadensis)
3. may say something about the
way the species is used (e.g.
Avena sativa – cultivated oats
from the Latin for cultivation
4. may say something about the
character of the species (e.g.
Acer rubrum – red maple,
from the Latin for red – ruber)
To complete the proper naming of a species, the species name
may be followed by a subspecies, variety or cultivar name. For
example, there are a number of varieties of Solidago
canadensis.
The local variety is Solidago canidensis canadensis.
After the formal name is designation, by initial or short form,
of the person who first described the species. If the taxonomic
position of the species was changed, or if the descriptive
information did not place it in a specific genus, the name of
the person who placed the species follows.
In the case of the goldenrod, Linnaeus named and placed the
species within the genus, so the full proper name is:
Solidago canadensis canadensis L.
Nomenclature at higher taxonomic levels may also be
descriptive of group characteristics. A few examples:
Hydrocharitaceae – with that first syllable, where do you think
they live? They are aquatic plants, often submerged.
Umbelliferae – their flowers are organized into a flat headed
group that bears a resemblance to an umbrella
There are also descriptive terms that define:
• inflorescence types
• fruit types
• stature (bush, shrub, herbaceous)
• petal or corolla types (fused, without petals (or apetalous)
• and shapes of petals (e.g. spatulate or spade-like)
Linnaeus’s initial classification was very controversial,
because he developed it from the sexual characteristics of the
male parts, and did it (in Latin, of course) by close analogy
with human sexuality.
stamens were “husbands”
pistils were “wives”
hermaphroditic flower “husband and wife share the
same bed”
two stamens fused together = “two brothers in love”,
which modern botany calls diadelphous (less
controversial?)
You can imagine how some of the terminology, e.g. the last
one, must have gone over with religious scientists (and
basically at the time all were).
Your text has a quote from Johann Siegesbeck in response to
this approach to taxonomy:
“such loathsome harlotry as several males to one female
would not be permitted in the vegetable kingdom by the
Creator…Who would have thought that bluebells, lilies, and
onions could be up to such immorality?”
Are we now in a position to test our ability to taxonomically
categorize plants? Let’s find out. What follows is the
description of the Rose family that is the basis of taxonomy
for the group…
Rosa L.
Hypanthium globose to urceolate with a constricted orifice; sepals
usually long-attenuate or prolonged into a foliaceous tip, often persistent
in fruit; petals large, spreading at anthesis, white to yellow or red,
stamens very numerous, inserted near the orifice of the hypanthium on
relatively short filaments; ovaries mostly numerous, inserted on the
bottom or also on the sides of the hypanthium; styles usually barely
exerted, distinct or united. Mature hypanthium commonly coloured,
pulpy or fleshy; shrubs or woody vines, usually prickly; leaves pinnately
compound with 3-11 serrate leaflets…
Terms:
hypanthium – basically a tubular calyx
globose – spherical, globe-like
urceolate – urn shaped
foliaceous – leaf-like in flatness, color and texture
anthesis – the time when the flower is fully expanded and
functional
Here are some pictures to identify those characteristics:
persistent sepals
prolonged into a
“leaf-like” tip
Mature hypanthium
“pulpy or fleshy”,
red-coloured
leaves pinnately compound
petals large,
spreading at
anthesis
Stamens yellow,
inserted near the
orifice of the
hypanthium on
relatively short
filaments
styles distinct
ovaries numerous
shrubs or woody vines,
usually prickly
Why be concerned about taxonomy?
1. Understanding the order in life is necessary to
understanding evolution and ecology
2. Without taxonomic structure and identification we would
not be able to measure biodiversity or assess extinction
3. (Think here of “Medicine Man”) To find new food and
medicines we need to know exactly what species produced
the useful product. To adopt biological control strategies, we
need to know what species are involved in ‘useful’
interactions.
4. There are many toxic or harmful plants out there. To protect
ourselves, we need to be able to identify them.
The taxonomic diversity we see today arose through evolution.
You need to understand the underlying principles of
Darwinian evolution to:
1. make sense of plant ecology,
2. understand approaches to agriculture consider here what a
mess Minchurin and Lysenko made of Russian agriculture
with their belief in and policy decisions based on the
inheritance of acquired traits),
3. make sense of many of the controversies about moving
species around (for example, in the construction of the
Windsor parkway, or in broader approaches to conserving
rare or endangered species)
4. and about genetic engineering of species.
There are four underlying components to Darwinian evolution:
1. There is variation evident among members of a species.
Darwin understood that this variation must be heritable for
evolution to work, even though he did not understand the
mechanism of heredity.
2. Every species is capable of growing in numbers to the point
of overpopulation. The number of offspring produced is in
excess of the number that can survive.
3. Given limited resources (that is the reason not all offspring
will survive), there will be “a struggle for existence”. We
call this intra- and interspecific competition.
4. Among the variants present, some are better suited to their
environment and/or the competition among them. What
results is “the survival of the fittest”.
We call that last statement “natural selection”.
Natural selection is the basis for most (though not all)
evolution.
Is natural selection the only form that selection can take?
No! An important part of the way Darwin came to understand
natural selection was to recognize that humans have
caused/driven selection for traits we want. When we drive the
selection, it is called artificial selection.
How do we do it?
By selecting and retaining individuals who bear the traits we
want. Darwin knew about artificial selection from doing it in
raising pigeons.
Varieties of pigeons from Darwin’s The Variation of Animals
and Plants under Domestication…
There is another example of artificial selection that should be
even more familiar to you.
How did we arive at the large number of breeds of dog we
now raise? Artificial selection, of course!
Brussels griffin – 3
kg full grown
Golden retriever ~ 30 kg as a full
grown adult
malamute – ~40 kg
or more
Artificial selection is also the way we get highly productive
milk cows. Sires that father highly productive cows have very
valuable sperm that is collected by fooling the bull into mating
with an artificial cow rear-end and harvesting the sperm.
Cows are artificially inseminated with that sperm.
The process of artificial selection is progressive. In each
generation we push the process a little further, until the
response declines.
Note that we are selecting traits we want and breeding
individuals carrying them, independent of natural fitness.
In addition to selecting among natural variants in artificial
selection, we can now induce variation and use it.
Discussion question: How does induced variation fit into
concerns about genetic engineering?