Thursday, April 5, 2012

Whatever Became of the Snapdragon Family?

For centuries, botanists have grouped similar plants into the taxonomic category of family.  Plant families are a very important way of recognizing relationship and predicting useful characteristics.  For example, if we find a valuable medicinal property in one member of a family, we are more likely to find similar properties in other members of the same family than in species outside the family.   Recently, I wrote about the important Grass Family, and the similar edible properties of many grain species in the family.  Other familiar families include the Rose (Rosaceae), Tomato (Solanaceae), Legume (Fabaceae), and Sunflower (Asteraceae) Families.

Butter-and-eggs, or Linaria vulgaris, is a
close relative of the snapdragon, and
no longer in the Scrophulariaceae.
The Snapdragon Family (Scrophularaceae, also known as the Figwort Family) used to be a happy but rather large family that included snapdragons, mullein, monkeyflowers, foxglove, veronica, torenia, Indian paintbrush, calceolaria and many other attractive garden and wild flowers.  It is not a major family for medicinal plants, but the foxglove is the source of the important heart stimulant, digitalis. Many other members of the family (e.g. snapdragons themselves) provide ornamental bedding plants worth millions worldwide.

Sadly the snapdragon family has suffered a nasty divorce, and what we now call the Scrophulariaceae no longer contains the snapdragons.  The old Scrophulariaceae has in fact been split into at least six smaller families (Olmstead, et. al 2001). The pieces, it was found, were not closely related to each other, some pieces were actually closer to other families, including the mint, gloxinia, and verbena families.

The family is a victim of the more precise analytic tools of the late 20th century and the new phylogenetic taxonomy. The similarities among the members of the old Scrophulariaceae were superficial, it turns out. The general flower shape and form of the seed capsule evolved many times from different ancestors (convergent evolution) because they were adapting to similar pollinators and seed dispersal strategies. In sum, the old family was polyphyletic

The story involves all the drama and complications of modern plant taxonomy.  For two centuries, botanists have worked to define more "natural" families.  Natural families contain genera that share fundamental characteristics, including similar structural features of flowers and fruits.  In the late 19th century the word natural took on the new meaning of evolutionary relationship.  Following Darwin's lead, biologists interpreted fundamental similarities within families, genera, and other categories as due to common ancestry.  For the next century or so interpretations of natural similarity and evolutionary history went hand in hand.  More and more information from anatomy, chemistry and genetics became available, often confirming, but sometimes toppling earlier assumptions about relationship.  The information available became so huge that putting it altogether into a master classification of plants relied on the experience and gut feelings of a handful of the leading taxonomists.  But the classifications of these wise old men often differed markedly, as much of the information could be interpreted in different ways.

In the middle of the twentieth century, there were many attempts to decipher evolutionary history (or phylogeny) with rigorous and objective statistical tools.  The most successful of these was cladistic analysis, a process in which similarity among a group of organisms was distilled into distinct and narrowly defined characters, and the organisms sorted out based on the number of shared characters.  Organisms with the most shared characters came out close together on a tree-like cladogram.  The branches of the cladogram were then grouped into taxonomic categories, and the cladogram was also interpreted as representing the evolutionary history of the group (i.e. as a phylogenetic tree).  Cladistic analysis,now routinely applied to structural, chemical, and genetic data, remains the core of systematic biology.

This lousewort, Pedicularis bracteosa,
 is now in the Orobanchaceae.
So then, where did the snapdragons end up?  The snapdragon genus (Antirrhinum), along with foxglove (Digitalis), Penstemon, Veronica, and butter-and-eggs (Linaria) ended up fortunately together, in what might now be called the new Snapdragon Family, or technically the Plantaginaceae.  The very similar-looking monkeyflowers (Mimulus) are only distantly related and have been moved to the family Phrymaceae.  Indian paintbrush (Castilleja) and Pedicularis now belong to the Orobanchaceae, which contains mostly parasitic species. Torenia is in the Linderniaceae, and Calceolaria is in the Calceolariaceae.  What remains in the Scrophulariaceae are the figworts (Scrophularia), Mullein (Verbascum) and some other original members, with the addition of  some genera that used to be in other families, including Myoporum and Buddleja

Nothing is more snapdragonish than a
monkeyflower, but this common western
American genus is now in a family
no one has heard of - the Phrymaceae.
Confused?  Don't worry, most professional botanists and horticulturists are as well.  Many websites are still using the name Scrophulariaceae in its original broad sense.  It's a trainwreck out there.

Plantago is a genus of weedy,
wind-pollinated herbs, that is
unfortunately atypical of the
new Snapdragon Family. Photo by Bernd Haynold
Source:http://upload.wikimedia.org/
wikipedia/commons/2/29/
Plantago_lanceolata_040807.jpg
The name of the new Snapdragon Family, Plantaginaceae, is a real irritant to many of us old-timers.  It is based on the genus Plantago, a genus of small, inconspicuous, wind-pollinated herbs known as plantains (not the big cooking bananas!).   Because of its highly reduced flowers, its relationship to snapdragons, etc., was not recognized, and it had been in its own family, Plantaginaceae, for centuries. 

Veronica was the basis for the proposed
family name Veronicaceae.  This name was
preferred by many, because at least it was
more symbolic of the types of flowers found
in most members the family. Plantaganiceae,
however had priority.
The name Veronicaceae was originally suggested for the new family (Olmstead et al. 2001), but according to the rules of taxonomy, an existing family names take precedence over a new family names, and since Plantaginaceae has been recognized as a family much longer than the Veronicaceae, the older name must prevail, and so the Snapdragon Family is now officially the Plantaginaceae.  Plantago represents a tiny specialized twig of the snapdragon family tree, and it is too bad to name this family of colorful, distinctively shaped flowers for such an atypical member. This tail-wagging-the-dog result seems counterintuitive and hard to accept, but for now that's the way it is.

The old Scrophulariaceae was polypheletic, and in order to create families that represented genuine evolutionary relationship, it had to be broken up.  Other traditional families have suffered a similar fate, including the Lily Family, Liliaceae.  Daylilies, for example, are no longer in the Lily Family - but that's another story.

Reference: Olmstead, et. al. 2001.  The Disintegration of the Scrophulariaceae.  American Journal of Botany 88:348-361.

2 comments:

  1. If a plant were named specifically for it's beauty, then certainly Plantain would not be a great qualifier. However, if a plant is named or categorized after other constituents,such as chemical compounds, growing habits, or usefulness, then the Plantain would be a winner. Highly nutritious, medicinally important and readily available, Plantain is an amazing species. The question is, does Snapdragon fit in with Plantago in other ways other than beauty or not?

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  2. I just stumbled on this blog after looking up information on the fig-wort family for a paper and finding wikipedia to be woefully out of date.

    I think you should go and freshen it up!

    ReplyDelete