Journal Number 100
August 2006

ORIGINAL PAPERS

To Split or to Lump?  That is the question
by Bruce Irwin, Tauranga

Graeme Jane's "Plant Names" [J98 p10] discussing Caladenia alata, explained succinctly some relevant rules of the International Code of Botanical Nomenclature (ICBN), and how they should be interpreted. But clearly the rules of nomenclature were resolved by experienced botanists for the guidance of other botanists. Taxonomy is not a primary school subject, but some understanding of it is necessary when discussing an apparently new species.

One very real difficulty in achieving the correct interpretation of the rules, is the fact that people, like plants, can and do exhibit considerable variation. For instance many amateur botanists, finding an orchid which shows a noticeable difference from others in the same colony, consider it to be  a separate species. They apparently overlook the very many similarities it shares with all the others in the colony. Such people may be regarded as "splitters"

Other generally more experienced botanists, though they may see that the plant shows an apparently significant difference, notice also the many more important similarities.
Such people may be regarded as "lumpers". Which attitude is correct?

Perhaps these terms should be applied only when a person splits or lumps without having given the matter sufficient thought, or has done so against ICBN rules or sound advice from others.
A botanist should split when it is clearly appropriate to do so. Let us ponder the problem for a while.

The first thing we should consider is that differences and similarities should be of structure, not of colour. Colour alone is not accepted as indicating a separate taxon. Colour is magic. Clear blues, reds and yellows can combine to make a deep glowing black. I have demonstrated this truth to many students of watercolour. They have read that this is so, but need to see it happen before they really believe it. Yes, colour is magic, but don't be seduced by it as so many splitters have been. I shall make one concession. Unusual colours may indicate that structural differences may also be present.

Referring again to students of watercolour, they know that trees are green, and they know that blue and yellow combine to make green, so their early attempts to match foliage result in a horrid hue resembling bile. They find it difficult to accept that leaves contain a certain amount of red. Below a certain strength, red barely affects the appearance of green, but being a very powerful pigment, at greater strengths it can overpower the greens.

Many of you will notice that some Pterostylis plants, such as P. agathicola, P. irsoniana and
P. irwinii, appear to have red or brownish stems, and their flowers and leaves are striped red, whereas others in the same colony may show only pinkish sepal tips and are otherwise completely green. A very small variation in strength of red pigment causes a significant change in appearance. See Dan Hatch's note in J99 p16.

Splitters will argue that rare and endangered species cannot be adequately protected until their existence is documented and they are formally named. On the face of it, that seems logical. But however conservationists may plan to protect them, deer, pigs and possums are not impressed. If a plant is a tasty morsel they will eat it, named or not. Life is a struggle for many small plants, and they are often found in poor soils. Is that what they prefer?

Perhaps not. I am inclined to think that competition from more vigorous plants often dictates where they can grow. To protect orchids it may be necessary to control more vigorous plants. Possibly to avoid competition, orchids are sometimes discovered in swampy habitats, so it is presumed that that is what they prefer.

Thelymitra aemula is such a plant. It comes as a surprise to find it flowering happily alongside
T. matthewsii on sun-baked eroded sandstone, where it has few competitors. Such plants should not be thought of as distinct species merely because they have chosen to grow in a very unusual habitat.

It is important not to lose sight of closeness or distance in relationships between species. Relationships are the very basis of the binominal system of naming plants. We need not be concerned about the higher taxonomic categories. Generic and specific names are our concern.

The name Corybas conveys a general impression of plants within the genus, because it groups together plants which are very closely related. The specific name trilobus defines the plant which differs sufficiently to be considered a separate  species.

One difficulty is that there are roughly as many concepts of a species as there are botanists. Hence the existence of splitters and lumpers. Once orchid enthusiasts have become familiar with the names of species in the genus Corybas, it is disconcerting to find that Australian splitters, with the bit firmly between their teeth, have split the genus Corybas into several smaller genera.

Several species were transferred to Nematoceras (an early name for Corybas in New Zealand), but other New Zealand species have recently been given quaint generic names such as Anzybas, Molloybas and Singularybas.

Hopper and Brown point out that these could have been placed in separate sections within Corybas or treated as subgenera, in which case the need to learn a new name would be avoided, as would the outcry from botanists throughout Australia and New Zealand. The ICBN seeks to maintain stability of plant names.

Another point worth remembering is that it is not mandatory to accept a new name just because it has been published. A validly published old name remains valid provided that when used, it is followed by the author's name or an abbreviation.

My contention that 7 or 8 separate taxa were lumped under the name Corybas rivularis s.l. branded me a splitter - a rather reluctant splitter. I had set out to map the distribution of the 2 forms of C. rivularis I then recognised, but time and time again, quite different forms showed up which could not be placed within either of the first two plants, now named Nematoceras iridescens and N. papa.

Now I should like to indulge in a little lumping - I predict that Thelymitra "darkie" which can be found on well drained hillsides as well as in rather moist habitats, will be recognised as identical with T. "ahipara", which was discovered  in exceptionally wet habitats, and presumed  to be confined to them. Why do I say this?

• Both plants have the same unusual  chromosome number -  4n = 60, a number not shared by any other New Zealand species.
• The columns of both are indistinguishable.
• The rather paler colours of T. "ahipara" cannot be regarded as a reliable diagnostic character.

Do I prefer lumpers to splitters? Both have a place within taxonomy. The problem is keeping them in their place.

I thank Graeme Jane and Dan Hatch for helpful comments, and Dan for putting this on disk.