Tuesday, August 8, 2017

Families Matter

You probably remember from introductory biology course, that the official way of naming a species is the binomial ("two-name") system. Each species name is composed of the genus name and the specific epithet.   For example, Quercus alba is the name for the white oak.  Quercus is the genus, which contains a number of other species of oaks, and alba is the specific epithet that refers exclusively to this one species.

In almost all scientific communication and labeling practices, however, a third identification tag, the family name, is added - e.g. Quercus alba (Fagaceae). This greatly increases the utility and comprehensibility of the naming system.

The binomial system itself evolved from a fundamental human instinct to recognize categories of things, and specific types within those categories. Before Linnaeus established the formalized latin system that gave us Quercus alba, there were "white oaks, red oaks, etc. (and the equivalent in various other languages), just as there  were John Smith, William Smith, etc. Referring to just a "white" or "John," or "William," doesn't tell us much at all.

The  binomial gives some context to a name, and helps us interpret new information.  If someone describes a new species, Quercus antarctica (hypothetical) for example, we immediately know that it is another species of oak.  We can predict that it will be a woody tree or shrub with simple leaves, and that it produces acorns. The family name adds another layer of recognition and predictiveness.

Suppose, for example, someone comes into the room raving about the spectacular specimen of Trigonobalanus doichangensis she'd seen at a botanical garden in Singapore.  I myself would have stared blankly at her, having no idea what that gibberish stood for.  But then she tells me that Trigonobalanus is a genus in the family Fagaceae.  A big light bulb turns on in my head. Fagaceae is the family to which Quercus belongs, along with Castanea (chestnuts), Fagus (beeches), and several other genera. Suddenly I have an approximate idea of what this plant is.

The family name is therefore extremely valuable for recognizing, characterizing, identifying, labeling, storing, retrieving, and providing relationship context for plant specimens. Sometimes it is of more value than the genus name for providing a rough idea of what a plant is and where it fits in relationship to other plants, as in the Trigonobalanus example above. This requires, of course, some knowledge of plant families. Learning the characteristics of families is a routine part of studying plant taxonomy, but will also be highly useful to anyone with an interest in plants.  Even the use of common names like "the orchid family" or the "iris family," etc., will be helpful when communicating with a lay audience.

The taxonomic system is a hierarchy of taxonomic categories, or taxa. Genus and family are two levels of taxa.  Theoretically, we could also append the names of higher categories, like orders, classes, phyla, etc. You will find those in textbooks, but for everyday use, they would amount to information overload. We can refer casually to important higher categories, like angiosperms, gymnosperms, green algae, etc., without really worrying about their technical names or their rank (their level within the hierarchy).

In this botanical garden label, the binomial, Galium odoratum, is most prominent.  Much additional useful information is also included, but most importantly, the family name, Rubiaceae, is included, in this case at the top left.  Incidentally, purists will point out that the binomial, by convention should be italicized, but that is not always possible.  Often, the machines that make labels do not have an italic font capability.  In fact, the formatting tools for the host service under which this blog is created does not allow for italics in the title, as can be seen in my posts on moss genera.
Photo copyright Oxford University, fair use. 

Familly names for plants have been standardized with the "aceae" ending, which is attached to the name of the first named genus in the family  The Asteraceae (sunflowers, etc.) gets its name from the genus Aster.  So you'll know when you're seeing a family name.  Some older names were different, ending in "ae,"  and using a descriptive term instead of a genus name as the base.  The old name for the Asteraceae was the "Compositae," referring to the composite or compound nature of the flower heads.  You will still see these type of names in the older literature.  Some of the other common ones are "Palmae" (for Arecaceae), "Gramineae" (for Poaceae), "Leguminosae" (for Fabaceae), "Labiatae" (for Lamiaceae), "Crucferae" (for Brassicaceae) and "Umbelliferae" (for Apiaceae).

The point(s) of these remarks are several:

1. For botany instructors and students, learning the characteristics of the plant families that occur in your area, and using plant family names when labeling or referencing specimens, has a huge practical value.

2. When identifying plants, recognizing the family narrows down your search and allows you to skip over what is usually the most difficult part of a taxonomic key.

3. Referencing the plant family when writing or talking about plants puts them into a context of relationship.  The taxonomic system is not an arbitrary set of names, but reflects the natural evolutionary relationships among plants.

4. For practicing taxonomists, we need to keep in mind the practical value of maintaining a manageable number of stable families with meaningful, recognizable, distinguishing characteristics. That's not always easy, given the directive of modern phylogenetic taxonomy to reorganize plant diversity into strictly monophyletic taxa, which often requires splitting of old familiar families into smaller units, or lumping familiar families into larger families with more diverse characteristics.  

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