Checking through the index for Journals 1 to 101, the Column stalled on key word entry, "species define" with no less than nine entries because this basic precept of biological science still eludes clear definition, ever since the absolute species expectation, inherited by Linnaeus, fell from favour as Darwinism became the darling of the scientific community.

Let's have a look at these nine entries and see if a clear definition can thus be gleaned:

J54:23 June 1995. Bob Bates, [1]

The term "species" is applied to any group of genetically isolated organisms sharing the same gene pool. Individuals within species all look similar and breed freely with each other. They do not normally interbreed with members of other species: it's not that they can't, it's just that they don't, under normal circumstances because of a combination of the .following - geographical isolation, different flowering times, different pollinators, sexual incompatibility (from mechanical, chemical or genetic barriers).

Bob's definition of differing species can thus be summarised in the phrase which the Column has used before: Different species are taxa following different evolutionary paths.

Bob had been campaigning since 1981 [J40:10] to get some six (reduced to five, J79:30) South Australian taxa of Linguella (was Pterostylis) nana agg., recognised as distinct. They all had minor structural differences but principally, the four bulleted reasons above ensured that these taxa remained isolated so Bob held out against stolid conservatism that they should be different species.

His five tagnamed taxa are covered principally in J37:21; 40:10; 49:26; 79:30; 84:12 and 88:26. The five do not include Hoffman & Brown's nine L. aff. nano variants from southwestern Australia [2]. Even in 2002, David Jones and Mark Clements, using DNA and morphological criteria [3], recognised only one Linguella nana among a total of four only Aussie Linguella's, however David Jones' 2006 text [4] recognises about 30 Linguella taxa, all but five unnamed. So it would seem that in the intervening four years, Bob's well researched plea for basic species definition is now being taken seriously.

J56:28 September 1995, Dr. C. Bower, [5]

(Species are) groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups.

Dr. Bower goes on, "Although somewhat technical, this definition stresses reproductive isolation which means that, if two closely related orchid variants cannot interbreed because they are reproductively isolated, they are different species."

Dr. Bower and Bob Bates are "singing the same song" it would appear but for different reasons: the former re an increase in Chiloglottis species from five in 1987 to 29 in 1995 and the latter because of tardy recognition of at least five South Australian Linguella aff. nana taxa.

J68:13 September 1998, Bruce Irwin. [6] first quotes B.D. Jackson [7] from 1928;

(A species is) the aggregate of all those individuals which have the same constant and distinctive characters.

Then Bruce quotes from a 1963 Chicago publication [8] which stated, "A species is a population of individuals that are more or less alike and are able to interbreed and produce fertile offspring under natural conditions."

But neither is clearly definitive especially for Bruce who was then well known for defining eight of the Nematoceras rivulare agg., (J47:8 & J55:24), three reviving early descriptions (N. longipetalum, N rivulare s.s. & N. orbiculatum) but only two others of the eight have been recently described from his work (N. papa & N. iridescens) because, we are told, the other three look too similar as herbarium specimens (J79:16). So Bruce wrote his own definition as...

"A species is a group of individuals which may show minor variations among themselves. There may be quite considerable variation between their extremes but individuals within the group exhibit a more or less smooth transition between those extremes. There should be a distinct gap between the group and members of any other species in the genus."

Still not an absolute definition and it clouds the distinction between similar species such as Pterostylis australis, P. banksii and P. patens which have often been reported as transitioning from one to the other in adjacent colonies, [Nsltr 23:11; J70:6; 78:15; 79:3].

Bruce elaborates in his article on some of his definition's perceived shortcomings, in particular, self pollinating species and spontaneous creation of polyploids; i.e. Drymoanthus adversus with 4n = 76 chromosomes being almost certainly an autotetraploid derivative of the diploid, D. flavus with 2n=38 chromosomes. Bruce favoured "subspecies and varieties" [pers. comm. 4 Dec. 2006] to cover isolated taxa that Bates, Bower and the Column would prefer as species.

J79:30 June 2001, Doug Bickerton, [9] introduces allozyme electrophoresis for gene analysis and differentiates among some of Bob Bates's Linguella aff. nana species but doesn't get into species definition.

J79:33 June 2001, Henrick Pedersen [10] also delves into genetics and states --

Species are designated taxa complying with the biological species concept in a modern, botanically focused sense. In addition to mutual reproduction isolation they are distinguished by basically different genome compositions - a fact that can be utilised when assessing the rank of allopatric (from distinct areas) taxa. It is tentatively suggested that autotetraploid taxa should he treated as co-specific with their diploid progenitors. [i.e D. adversus = D. flavus, what?]

Henrick's spin in "the biological species concept in a modern, botanically focused sense" fogs his definition and his opinion that autotetraploid's be classified the same as the diploid parent seems to be a result of identification problems with multiple Dactyloriza orchid species in Europe.
See J93:38 for an update.

J91:4 June 2004, an anonymous contributor to the web, puzzles over yellow shafted and red shafted flicker birds hybridising in eastern North America and he or she writes, The definition of a species is that individuals belonging to one species .shouldn't be able to mate easily and produce vigorous, reproducing off-spring with individuals belonging to another species.

The contributor is clearly not versed in orchids where species and genera interbreed quite vigorously when given the opportunity but, like flicker birds, interbreeding is less common in nature where diversity is championed.

J98:19; February 1998 & J100:14 August 2006, Dr. Graeme Jane sets out the requirements of the International Code of Botanical Nomenclature for describing a species including the brief Latin diagnosis etc. but doesn't deal with the crucial issue of what defines a distinct species in the first place.

Discussion

Did we get a clear definition of "species" after considering all these learned attempts? The answer can only be, not quite but nearly. One of the major stumbling blocks has been the attempts to define a species instead of the difference between species.

The Column's contraction of the Bates/Bower definitions, that Different species are taxa following different evolutionary paths, is submitted as the key to deciding which are distinct species and which are not although this still leaves the decision to the taxonomist's personal opinion and that must be conditioned by what referees are asking for these days in the way of morphological differences, DNA checks and chromosome numbers.

So similar looking taxa will still remain classified as one species, won't they? Also, taxa may need a millennium or two of trivial mutations and adaptations to show enough morphological and/or molecular differences to clearly separate them.

Bruce Irwin [J 100:18] mentioned a good test case with two such close taxa in Thelymitra "darkie" and T. "Ahipara" both with 4n=60 chromosomes. Bruce opined that they were actually one species. Well, T. "Ahipara" is paler in colour in stem, bracts and tepals but otherwise it is very similar morphologically to T. "darkie. However, there are differences which could have evolved over the millennia; e.g. T. "Ahipara" prefers wet lake sides (but still grows on tracksides at Albany Scenic reserve) and thrives on seasonal inundation but T. "darkie" avoids the inundation. T. "darkie" flowers do open, if rarely, from mid October to early November whereas T. "Ahipara" is cleistogamic i.e. self fertilising without opening (except in a steaming car boot J67:24) but reaches maturity later in mid November [11].

The Bates/Bower/Column definition of species difference, would class these two taxa as distinct. Molecular confirmation of one stance or the other would be of some distinct interest.

Some of the possible contrary arguments mentioned above are discussed here including ---

1. Self pollinating species .

These are mostly fall-back self pollinators, e.g. Thelymitra longifolia which still open their flowers to attract the more successful evolutionary process of cross pollination whenever possible. For example, occasional crosses are purported to have occurred, with T. longifolia as one parent, such as the amphidiploid (doubled chromosome J68:28) hybrids T decora, T. hatchii and T pulchella, according to Molloy and Dawson.

In addition, the rare successful mutations in self pollinators that have occurred over the millennia (from DNA transcription errors, damage from cosmic rays due to cataclysms in the galaxy etc.), produce slightly different colonies in numerous areas. These do not gain the advantage of cross fertilising out the weaker genes but the differing colonies would still compete for territory.

Some must gain ascendancy (although never as speedily as with cross pollinating species) as
separate taxa such as T. aff. longifolia (insect pollinated and steadily deposing putative parent
T longifolia from the far north), T. purpureo-fusca Col., Bruce's subalpine T. "Whakapapa" and numerous other lesser variants at present all lumped as T. longifolia.

2. Polyploidy.

Successful natural polyploids such as tetraploid Drymoanthus adversus, which is notably more successful and more widespread than putative parent and diploid, D. flavus, is also structurally different and prefers a distinctly different habitat. They are indubitably following different evolutionary paths thus should surely retain the right to distinction.

Hexaploids (6n chromosomes) are rarer but Dan Hatch hypothesises that Thelymitra "rough leaf" ( Fig. 31 ) with 6n=84 chromosomes, is an hexaploid hybrid of diploid T. aff pauciflora (2np=26) and tetraploid T. "darkie" (4nd=60). This gives base numbers np=13 and nd=15, thus np+nd=28 and 3x28=84 chromosomes as for T "rough leaf'.

The arithmetic is right but some molecular confirmation would be of notable interest. In any case, polyploid T. "rough leaf' is a quite distinct taxon on a different evolutionary path from its putative parents so it is definitely a candidate for specific status just like the amphidiploids.

3. Similar appearance of herbarium specimens or the rumoured reason for continued non-recognition of three of Bruce's Nematoceras rivulare agg., doesn't add up.

Bruce's immaculate drawings clearly show internal structural differences which would show in sectioned specimens even when pressed or in spirits. Bruce reminded the Column (pers. comm. 4 Dec.2006) that he didn't ever "claim that they were specifically different." However, there are clear distinctions even if whole flowers deformed by the pressing could look similar.

But taxonomists are no longer wedded to the hallowed herbarium specimens when modern transport and methods can whisk live specimens around the world (with CITES approval!) before they wilt and photography can easily show the living differences.

Conclusion

With DNA analysis now in the ascendancy, one can only hope that our top world taxonomists can agree upon a definite and indisputable definition of species difference from molecular studies.

Perhaps an agreed mean nucleotide difference between specified genes for plants of like chromosome counts? Just think of all the host of new classifications such a decision would deliver to us!