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-the-world 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-woodosage applehedge applehedge osagehorse applemock orange

But the last common name ismore commonly appliedto a different group offlowering shrubs in the genusPhiladelphus

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 calyxglobose – spherical, globe-likeurceolate – urn shapedfoliaceous – leaf-like in flatness, color and textureanthesis – the time when the flower is fully expanded and

functional

Here are some pictures to identify those characteristics:

persistent sepalsprolonged 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 kgor 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?