Journal Number 100
August 2006

ORIGINAL PAPERS

When Is A Species A Species?
By Graeme Jane, Tauranga

Many people assume that a tag name implies the existence of a species. That is not at all true.

For a name to be accepted a species it must be formally described according to the International Code of Botanical Nomenclature. This derives from the original work and concepts of Carl Linnaeus some 150 years ago.

Originally Linnaeus set out to provide a better system than that of common names which often provided several names for the same plant or used the same name for several different plants, especially across international borders. He could also see floral and other similarities between many common plants which provided a framework for identifying and naming them.

This led to the binomial concept where similar species were grouped in genera. The binomial name (or perhaps surname) provided a clear link between similar plants. At a higher level the genera were grouped in families, families in orders etc. As knowledge expanded some of these groups became very large so subgenera and subfamilies etc were added.  Also as the species became better understood subdivision was found desirable to describe the range of variation. Thus the species concept evolved to include subspecies, varieties and forms.

The last perhaps too recognised that many different cultivated plants derived from the same species through plant breeding (eg cabbage, cauliflower, brussel sprouts, etc) are all derived from the same species.

Today, the concept of a species is based on a formal description in Latin  (sometimes quite brief) setting out the key characters the author sees as distinctive about it, or sometimes only how it differs from a similar species.

A single preserved specimen (for plants, usually pressed) is then normally designated as the type specimen. It is usually a typical example, but where the plant is named before its full range of variation is known this may not be true.

In the past, a range of specimens showing the author's concept of the species may have been designated as a type, and prior to about 1930 a type  was not necessarily identified and must be now selected from the range of material the author had available at the time he prepared the description. This has occasionally led to what are now regarded as separate species being represented in the original type collection.

In other cases the original material has been lost (eg the Paris and Berlin herbaria were bombed during World War II). In cases where the description is clear and collection records are sufficiently precise, fresh material from the original collection site can be designated (as a neotype).

Perhaps the point of the above detail is to show the care that is taken in formally describing a species. Informal names (tag names) are widely used in New Zealand with over 200 tag names in use.  They often arise where an observer is not satisfied that a particular population of plants seen (perhaps on a single field trip) fits easily within the range of variation of a described species. It provides a label until more is known about the taxon.

Some tag names are used for varieties described in the flora which some people regard as distinct species. Sometimes their origin can be found in footnotes in the flora.

Sometimes the tag names are short lived because the population is later identified to have arisen through active hybridism (ie parents can be identified) or is seen in other areas to grade into a particular species. Also, perhaps consultation with colleagues and herbaria enables the population to be identified as falling within the range of variation of an existing species, possibly at one extreme end.

In many cases the name may be sustained for many years until someone finds the time (and money) to investigate the variation and show definitively that a particular status (not necessarily species, it could be a variety or subspecies) is appropriate. The status of some taxa is particularly difficult to resolve even through cultivation, breeding experiments and DNA profiling.

Hence many years, sometimes decades may be required to sort out a series of taxa (with separate tag names).  

Daisies can be particularly difficult because a high level of self fertilisation gives very uniform populations which produce a wide range of hybrids  when outcrossing occurs (sometimes with other genera).

In a few cases (it seems often in NZ) tag names are created by orphaning. The Australians (applying Aussie rules) often leave New Zealand taxa without a name when revising a genus.

This sometimes occurs where the distribution of an Australian plant formerly stated to include New Zealand no longer does so (ie the action is passive), or the author specifically states that the New Zealand plants formerly regarded as the same as the Australian are not.  In both cases the author is basically saying "you sort out your own mess"! Here the species may add an aff. (affinities) or cf. (compare with) to the original name (eg Thelymitra aff. ixioides).

Thus the use of a tag name does not define the plant as a species because it may not be supported by and identified with a herbarium specimen and certainly has not passed through the rigorous sieving process required ensure a sound decision has been made. Thus the status, whether species or variety (or sometimes even which genus it belongs to) has not been properly resolved.

The simplest first steps to sorting out relationships between apparently different taxa is to grow them under the same conditions either by cross-transplanting or by marking and observing the same plants over several years. Growing orchids from seed collected from the distinctive plants can also sort out how stable the variation is.

If the seed does not produce plants like the parent then you have a problem. These are useful steps a keen amateur can carry out perhaps to resolve some of the debates over the validity of tag names in use.