Plant Systematics

Woman Holding a Growing Plant
Yagi Studio/Getty Images

Plant systematics is a science that includes and encompasses traditional taxonomy; however, its primary goal is to reconstruct the evolutionary history of plant life. It divides plants into taxonomic groups, using morphological, anatomical, embryological, chromosomal and chemical data. However, the science differs from straight taxonomy in that it expects the plants to evolve, and documents that evolution.

Determining phylogeny - the evolutionary history of a particular group - is the primary goal of systematics.

Classification Systems For Plant Systematics

Approaches to classifying plants include cladistics, phenetics, and phyletics.

Cladistics. Cladistics relies on the evolutionary history behind a plant to classify it into a taxonomic group. Cladograms, or "family trees", are used to represent the evolutionary pattern of descent. The map will note a common ancestor in the past, and outline which species have developed from the common one over time. A synapomorphy is a trait that is shared by two or more taxa and was present in their most recent common ancestor but not in earlier generations. If a cladogram uses an absolute time scale, it is called a phylogram.

Phenetics. Phenetics does not use evolutionary data but rather overall similarity to characterize plants. Physical characteristics or traits are relied upon, although the similar physicality can reflect evolutionary background as well.

Taxonomy, as brought forth by Linnaeus, is an example of phenetics.

Phyletics. Phyletics is difficult to compare directly with the other two approaches, but it may be considered as the most natural approach, as it assumes new species arise gradually. Phyletics is closely linked to cladistics, though, as it does clarify ancestors and descendants.

How does a plant systematicist study a plant taxon?

Plant scientists can select a taxon to be analyzed, and call it the study group or ingroup. The individual unit taxa are often called Operational Taxonomic Units, or OTUs.

How do they go about creating the "tree of life"? Is it better to use morphology (physical appearance and traits) or genotyping (DNA analysis)? There are benefits and disadvantages of each. The use of morphology may need to take into account that unrelated species in similar ecosystems may grow to resemble one another in order to adapt to their environment (and vice versa; as related species living in different ecosystems may grow to appear differently).

It is more likely that an accurate identification can be done with molecular data, and these days, performing DNA analyses is not as cost prohibitive as it was in the past. However, morphology should be considered.

There are several plant parts which are particularly useful for identifying and segmenting plant taxa. For example, pollen (either via the pollen record or pollen fossils) are excellent for identification. Pollen preserves well over time and is often diagnostic to specific plant groups. Leaves and flowers are often used as well.

History Of Plant Systematic Studies

Early botanists such as Theophrastus, Pedanius Dioscorides, and Pliny the Elder may very well have unwittingly started the science of plant systematics, as each of them classified many plant species in their books. It was Charles Darwin, however, who was the main influence on the science, with the publication of The Origin Of Species. He may have been the first to use phylogeny, and called the rapid development of all the higher plants within recent geological time "an abominable mystery".

Studying Plant Systematics

The International Association for Plant Taxonomy, located in Bratislava, Slovakia, seeks "to promote botanical systematics and its significance to the understanding and value of biodiversity." They publish a bimonthly journal devoted to systemic plant biology.

In the USA, the University of Chicago Botanic Garden has a Plant Systematics Laboratory. They seek to put together accurate information about plant species so as to describe them for research or restoration. They keep preserved plants in house, and date when they are collected, in case that is the last time the species is ever collected!

Becoming A Plant Systematicist

If you are good at math and statistics, are good at drawing, and love plants, you just may make a good plant systematicist. It also helps to have sharp analytical and observational skills and to have a curiosity about how plants evolve!