DNA analysis is being used to refine the classification of ferns and to further define the relationships between them. In some instances, this work at the molecular level reinforces what has previously been established from morphology and other investigations. On other occasions, however, scientists find that the molecular DNA analysis is telling a different story and suggests that further work needs to be done.

Classifying ferns

Traditionally, organisms have been classified according to their observable features, their morphology. Frondsrhizomes and reproductive structures are all important in classifying ferns.

As technology has advanced, other techniques have become available, and these have been useful in refining fern classifications. In the 1960s, for example, the scanning electron microscope became more widely available. This microscope enabled scientists to look in great detail at the shape and character of fern spores. It was quite a revelation when scientists saw the huge variation in spores. In fact, they discovered that you could identify many genera and species of New Zealand ferns simply by the pattern of their spores.

More recently, using molecular techniques, scientists can extract and examine DNA from fern cells. This technology is being used to confirm species classification, as well as to determine how closely related different species are. It allows detailed analysis that can reveal information about the evolution and the relationships of different species.

DNA technology is very powerful, and it’s contributing to a renewed interest in taxonomy and biosystematics. As molecular information becomes available and as evolutionary relatedness is being determined at a DNA level, this is leading to revisions in classification.

Reclassifying ferns

Ferns have traditionally been classified into ‘ferns’ and ‘fern allies’. You’ll see this terminology in many textbooks and school reference material. These 2 groups reflected what scientists observed – there were some very odd ferns that didn’t quite fit the ‘fern’ classification criteria, so these were grouped together as fern allies. This meant that, while they weren’t recognised as being true ferns, they were closer to ferns than they were to anything else.

With DNA analysis, it became clear that some of those fern allies were in fact true ferns. An example of this is the Tmesipteris fork ferns. These were previously grouped with the fern allies, which also included the lycophytes Lycopodium and Selaginella. With DNA analysis, scientists established that fork ferns are actually more closely related to ferns than the lycophytes.

DNA analysis and family (phylogenetic) trees showing relatedness of ferns have resulted in the classification of extant (living) ferns being revised recently. Rather than distinguishing fern allies (which included the fork ferns) from ferns, the revised classification distinguishes ferns (now including fork ferns) from the lycophytes. It is also now known that the ferns are more closely related to the seed plants than they are to the lycophytes. The revised classification reflects the current understanding and is based on both morphological and molecular data.

Nature of Science

New technologies make it possible for scientists to extend their research and discoveries. The revised classification of extant ferns came as a result of molecular DNA analysis. Our current understanding of fern classification may be revised in the future as technologies advance.

Published 14 October 2010