Hosta an Asparagaceae? Are You Kidding?
Several shifts in taxonomy in recent years have sent those of us who try to keep abreast with such changes into a tailspin. Some of the most surprising changes have happened in the Asparagaceae family.
Changes were brought to my attention while writing outlines for Symposia for National Garden Clubs. I had decided to teach the Asparagaceae family to flower show judges. My research of Asparagaceae led to some unexpected revelations. I learned that several genera were in this family other than Asparagus; notably Agave, Chlorophytum, Cordyline, Dracaena, Hyacinthus, Ophiopogon, Liriope, Sansevieria, Yucca, Hosta, and about 116 other species.
Hosta? Really? You’ve got to be kidding! How is it that such seemingly diverse genera are in the same family? Formerly, Hosta was a member of the Liliaceae (lily) family, and then it was assigned its own family, the Hostaceae. Some taxonomists place Hosta in the Agavaceae family. My goodness!
How did this all evolve? Formerly, most taxonomic systems were based on morphology, or the form and structure of a plant. Newer models are molecularly based systems which more accurately reflect the phylogeny (evolutionary descent) of a plant. None of the above assignments were wrong; they were just different and based on the most accurate and reliable information available at the time. Scientists have learned that Hosta and Asparagus share a common ancestor.
I learned the ranks of plants by memorizing this sentence: King David cried, “Oh, for goodness sake!” K is for kingdom, D for division, C for class, O for order, G for genus, and S is for species. These ranks have been significantly changed in the APG III system. Now the rankings are clade, order, family, genus, and species. A clade is a taxonomic group comprising a single common ancestor and all the descendants of that ancestor. Clades within clades, or nested clades, are included. This arrangement helps to show the origin of each species as part of a very large Tree of Life, starting with the first single-celled organisms and including all life forms.
The Asparagaceae family belongs to the clade monocot and the order Asparagales, which has only recently been recognized with the advent of phylogenetics. Older classification systems placed many of the species now within the order Asparagales into the lily family. The recently added Asparagales order contains 14 families, including Amaryllidaceae, Asparagaceae, Asteliaceae, Blandfordiaceae, Boryaceae, Doryanthaceae, Hypoxidaceae, Iridaceae, Ixioliriaceae, Lanariaceae, Orchidaceae, Tecophilaeaceae, Xanthorrhoeaceae, and Xeronemataceae. Within the 14 families are about 1,122 genera and 26,070 species. The Asparagaceae family contains about 126 genera, including Hosta, Sansevieria, and many others.
A highly respected taxonomic system based on phylogeny is the Angiosperm Phylogeny Group system, called APG III. The APG III system of nomenclature is very recent, so it is not used in many textbooks. However, it is being used as the basis of the World Checklist of Selected Plant Families being compiled at Kew Royal Botanic Gardens. In the UK, the latest edition of the standard flora of the British Iles uses the APG III system. Missouri Botanical Garden’s website APweb (Angiosperm Phylogeny Website) is regularly updated using the APG approach. GRIN taxonomy, my favorite reference, is based, with a few more recent exceptions, on APG III classification. It is likely that it the APG III System of Taxonomy will become more and more influential and accepted as time goes by.
Most gardeners who grow plants for their personal enjoyment care little about plant families, and that is fine. It is those of us who write and teach about plants who worry about such fine distinctions. We must keep in mind that research continues, so a classification presents an opinion at a particular point in time based on current research. Classifications change as a result of research findings. Needless to say, this is somewhat inconvenient to users. However, the APG III publications are increasingly regarded as an authoritative point of reference.
If you are finding confusing data regarding plant family names, blame it on progress. Maybe one day the taxonomists will all be in agreement, but perhaps not. It is the continual research and new findings that keep scientists on their toes. While changes are sometimes frustrating to us laymen, we can feel sure that the scientists are trying to find the truth in matters of plant taxonomy. We are the lucky recipients of their newfound knowledge.
|Authors of the APG System include scientists from the Swedish Academy of Sciences, Uppsala University; Stockholm University, Royal Botanic Gardens, Kew, University of Maryland, Cornell University, University of Florida, Florida Museum of Natural History, Harvard University Herbaria, University of Missouri, St. Louis, and Missouri Botanical Garden. |
| USDA, ARS, National Genetic Resources Program.|
Germplasm Resources Information Network - (GRIN) [Online Database].
National Germplasm Resources Laboratory, Beltsville, Maryland.
URL: http://www.ars-grin.gov/cgi-bin/npgs/html/index.pl (09 December 2013)