Plant Classification, or Why do they keep telling me the family?

Agnes deLanvallei March 05

Modern Plant Classification: A hierarchical system organizes all living things in a pyramid, so that larger categories are made of a number of smaller ones. (see for example http://tolweb.org/tree/phylogeny.html).) Plants are in the Plant Kingdom, and classified to a particular Division, Class, Order, Family, Genus and Species within that. Most of the plants that dominate our earth today are flowering plants, Angiosperms. Angiosperms form a Division (or Superclass depending on your taxonomist). There are about 215,000 species of flowering plants, divided into about 70 orders and 420 families.

The Angiosperm orders are large and diverse. Historically botanists have used Angiosperm families as points of reference. When they describe a plant, they often give its common name, scientific name and family ( example 1 , example2). The idea is that although you might not know what angelica looks like, if I tell you its in the carrot family, then you will visualize it as "like carrot," with divided fragrant leaves and a flat compound flower stalk, not, like, for example, peas (bean family) with tendrils and narrow asymmetrical flowers or like grasses with thin leaves and inconspicuous flowers.

The current method of assigning plant family names is to use the name of one genus in the family and add -ceae to the root.

Kentucky bluegrass is Poa praetensis, the grass family is the Poaceae; aster is the common name for plants in the genus Aster, one of the biggest plant families is the Asteraceae; orchids include the genus Orchis and the family is Orchidaceae; roses are in the genus Rosa in the Rosaceae etc. [The ceae ending tells you that you are looking at a plant family name.]

In speaking about these groups in English, it is common to call them the grass family, the aster family, the orchid family, and the rose family, respectively. However, the point of including the plant families is to try to relate the plant under discussion to something familiar, so its fine to call the Poaceae the bamboo family; the Asteraceae the sunflower family, or the marigold family or the chamomile family; the Orchidaceae the lady slipper family; and Rosaceae the apple family if that aids communication.

References

Cronquist, Arthur C. 1981. An integrated systm of classification of flowering plants. Columbia University Press, New York.

Judd, Walter S., Christopher S. Campbell, Elizabeth A. Kellogg, Peter F. Stevens and Michael J. Donoghue. 2002. Plant systematics, a phylogenetic approach. 2^nd ed. Sinauer Associates, Inc., Publishers, Sunderland MA.

Woodland, Dennis W. 2000. Contemporary plant systematics. 3^rd ed. Andrews University Press, Berrien Springs MI.