A Modern Understanding Of The Plant Kingdom

Botanists now have advanced tools to help them understand the evolution of, and relationships among, plants. In the past, systematic botanists—those who study classification and evolutionary relationships between plants—depended mostly on characteristics from morphological studies (analyses of the form and external structure of a plant) as well as analysis of their different chemical compounds to produce classification systems. Today, modern molecular tools for studying the composition of DNA—deoxyribonucleic acid, which contains the genetic code essential to the development and functioning of all living organisms (except viruses)—have revolutionized botanists’ ability to classify plants. Now a botanist can classify a plant by the DNA sequence found in an individual species.

Plant Kingdom

The process is similar to what’s used to help solve a crime or absolve the accused. This technology, along with new analytical approaches, has provided a wealth of information that can be analyzed using phylogenetics—the study of evolutionary relationships among organisms (in this case, plants). Perspectives obtained from phylogenetic analysis can be used to clarify and test plant classification systems and to further understand the plant kingdom and the groupings of its components.

Beginning in the late 1990s, a group of systematic botanists created the Angiosperm Phylogeny Group (APG) to produce a more precise classification system for flowering plants (angiosperms). APG retains some parts of the Linnaean system, plant orders and families, and requires that plants be grouped by their descendants from a common ancestor; this is known as the monophyletic approach. As a result, the placement of many families has changed. The term clade—a lineage—is used to group naturally related orders, families, genera, and species.

This work has led to the placement of some plant families within others, resulting in species that were formerly in one family now being recognized as part of another. Information on these new concepts can be found through an online search of “Angiosperm Phylogeny Group.”

Studying plants this way, at the molecular level, has truly revolutionized our ability to determine the relationships between and among species, genera, families, orders, and other groupings used to categorize plants—giving us a much greater understanding of plant classification. The closer scientists get to understanding how plants evolved and are related, the greater the ability of those who work on applied aspects of plant biology—including plant breeders, medicinal chemists, biofuel scientists, conservationists, and others who apply plant biology—to help feed, clothe, heal, fuel, and protect a growing world population and its environment.

For example, consider Taxol (paclitaxel), an extremely valuable plant-based medicine originally isolated from the endangered tree Taxus brevifolia. The quantity of bark needed for the production of a single therapeutic dose meant that there weren’t adequate supplies for patients’ needs; scientists eventually found compounds in a related, widely available Taxus species, allowing this vital medicine to be produced in the quantities needed. Having a precise understanding of plant relationships provided new insights into the search for biologically active molecules needed to make a drug in short supply. Far from an ivory tower exercise, obtaining an understanding of the evolution and relationships of plants, combined with an accurate classification system, greatly benefits us all.

Through DNA analysis, plant scientists have determined that chocolate (Theobroma cacao) belongs to the mallow family (Malvaceae), which also includes cola, cotton, and okra.

Through DNA analysis, plant scientists have determined that chocolate (Theobroma cacao) belongs to the mallow family (Malvaceae), which also includes cola, cotton, and okra.