Fickle Plant Classification

<i>Alstroemeria saturne</i>
Alstroemeria saturne

One of the flowers that will live longest after it is cut is the Peruvian lily, or “lily of the Incas”. The blooms will last two weeks in the vase, but the leaves will not, so you are advised to strip off the leaves before putting them in water.

The popular names of this plant are, in this case, more or less accurate. Which is to say, they do originate in the Andes, but they have two centers of diversity: one is a winter-blooming group in central Chile, and the other is a summer-blooming group in eastern Brazil. From these points of origin approximately 90 wild species have developed, ranging from Venezuela in the north down to Tierra del Fuego.

They are also, in fact, lilies. The genus Alstroemeria, after some taxonomic revision over the last decade, has been, placed in the family Alstroemeriaceae. (They were once placed in the Amaryllidaceae with the daffodils.) The family also includes the genera Bomarea, Schickendantzia and Leontochir, and is part of the order Liliales in some taxonomies and included in the order Asparagales (in the class Liliopsida) in others.

Systematics is a part of natural science where controversy will never truly go away. Although all biologists agree that all living species can be traced back to a common ancestor, there is no common, all-inclusive consensus as to how everything is related.

When Linnaeus established the binomial nomenclature in the 18th century and began grouping living organisms together, he wasn’t even thinking of them as having a common ancestor. Rather he was just trying to bring some organization to the classification of organisms. Most Enlightenment naturalists felt that they were in the business of perceiving the logic of the divine plan, not describing a branching evolutionary scheme. It was believed that the similarities among species were a product of variations on themes that existed in the proverbial mind of God. Darwin’s theory of natural selection introduced a mechanism that provided a means for defending the idea that species were similar because of common descent rather than due to repeated tweaking of a heavenly mold.

Through the last half of the 19th century (On the Origin of Species appeared in 1959) taxonomies (i.e. theories of systematics) were based on identification of shared morphological traits. The more traits shared, the more closely related the taxa. The arguments in that era were over which traits were the right ones to use and what weight to give each trait. The early 20th century development of the field of genetics largely verified and clarified the taxonomies of the previous century, but the introduction of molecular genetics in the 1960s and the eventual analysis of shared genes by the 1980s, changed the study of taxonomy.

Willi Hennig
Willi Hennig

While relatedness was implicit in post-Darwin classifications, the systems were called ‘phenetic’ because they were based on traits that could be observed in organisms, but the ordering of the traits was entirely based on the erudition of the classifier, not a mathematical model. The presumption of evolutionary relatedness was brought to the fore with to the development of cladistics and phylogenetics. Multi-variate statistics were brought to bear on the question of which traits to use and how much weight to give each one. As more powerful computers became more accessible to more people, the analysis of data in this way became more commonplace and the phylogenetic approach became pre-eminent.

Arthur Cronquist
Arthur Cronquist

Arthur Cronquist, a botanist at the New York Botanical Garden, developed the most widely used phenetic taxonomy of plants beginning in the 1960s, before the advent of cladistics. He published the first edition of his The Evolution and Classification of Flowering Plants in 1968 (second edition 1988), 11 years before Willi Hennig issued Phylogenetic Systematics, the inaugural work of the cladistics movement. Cronquist’s system is still used by some botanists, but many have adopted the taxonomy of the Angiosperm Phylogeny Group (APG), which was published in 1998 and revised in 2003 as APG II. The APG system is based on the cladistic analysis of the DNA sequences of three genes, two chloroplast genes and one gene coding for ribosomes. It has drastically revised some parts of Cronquist’s system, particularly his Liliopsida class, which included all the monocotyledon-bearing plants.

The United States Department of Agriculture still uses the Cronquist system and still has Alstroemeria in the Liliaceae, while the Daviswiki, the “creative commons” for the California city that is home to the premier horticultural arm of the state university system, and the Atlas of Florida Vascular Plants keep the genus in the Amaryllidaceae. The International Society of Horticultural Scientists (ISHS), of course, uses Alstroemeriaceae name and is busy working out ‘genetic linkage maps’ among the wild species. The APG II (unchanged from the APG, in this case) recognizes the family and puts it in the order Liliales in the clade monocots.


One thought on “Fickle Plant Classification

Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s