Abstract: in this conversation between two imaginary cactophiles, some aspects of the Cactaceae taxonomy of the past 40 years, are critically reviewed.
THE THORN IN THE SIDE
Conversation about the taxonomic abuses on the concept of species
It is nowadays even more important to become aware of the
connection between Science and Philosophy and of the
superability of any philosophic position........
Bruno DE FINETTI, L'invenzione della verità, Trieste, 1934.
– My dear MARIA, I accept the fact that you refer to your beloved plants with nicknames and affectionate words, but don’t expect me to understand what’s the plant that’s becoming yellow and makes you worry if you keep calling it ‘my little bag’.
I could give you a better advice if you could at least indicate to which family or botanical genus it belongs. And please, don’t ask me to visit you, right now I’m too far from you!
– I understand, it’s an old argument between the two of us, you want me to memorize some unpronounceable names, and, when I have finally learned them, you old sages change them once again, telling me that those that were right the day before are wrong today.
– I agree, my friend, you have some good reasons!
Usually a taxonomic or name change is supported by arguments based on new observed data or, at least, on a new system whose criteria are made clear by the authors, but unfortunately this is not always the case.
– LUCIO, as usual you start with difficult words and I have troubles understanding you!
– I’ll try to make myself clear with an example. You’ll recall that Turbinicarpus jauernigii was described by FRANK with the species rank, and shortly after ZANOVELLO and BATTAIA recombined it as Turbinicarpus lophophoroïdes ssp. jauernigii treating it as a subspecies. In that case, to justify this recombination (name and status change), they adduced the fact that jauernigii is sharing, during its development from the seedling stage to the adult plant, not only the stem and root morphology (nothing exceptional so far), but even the morphology of the areoles and the spines with that of T. lophophoroïdes and has a distribution range close to that of T. lophophoroïdes, i.e., in the recombination, they emphasised some affinities that were indicating the two entities were sharing a common ancestor not too different from them and not too far away in time. Some years later, you’ll recall again, DONATI concluded, in a revision of the genus Turbinicarpus, adopted by DONATI and ZANOVELLO in their book Rapicatus and Turbinicarpus, that, even if the two entities are very similar, treating them as conspecific was inappropriate, and also in this case, they produced explicit reasons for their choice. A rather hasty recombination the first one, but with the undisputed merit of turning the attention on the ‘juvenile phases’, that are now receiving more consideration even abroad, and a return to the rank of species of T. jauernigii the second one. As you can see, the rank change has required a trinomial combination first, and then a binomial one. Sometimes the binomial must be changed for not strictly botanical reasons, but for reason connected with the International Code of Botanical Nomenclature (ICBN) and thus not very interesting altogether and tedious albeit certainly useful, and I don’t want to bore you with that.
– So you admit that I have some good reasons............
– Sure. You see, the systematic botany, like any other science, is a structure that reorganizes itself continuously, like an insect that as a grub eats and grows, and keeps changing even if this is not so evident, and eventually it undergoes very showy changes, passing through various stages, until it becomes an adult insect. The only difference is that Science never reaches the ‘adult’ stage. Research keeps producing new knowledge that not only accumulates, but sometimes requires deep reorganizations (Physics provides very good examples of this). Back to taxonomy, in some cases it happens that a very fruitful and convincing choice applied to a certain area, generates a great temptation to extend its application in an ‘ideological’ and un-scientific way. This gives birth not only to useless recombinations, but also to superficial revisions of entire genera and, bit by bit, of a vast portion of a family, and this only to make the nomenclature match with the ideology, with the typical mechanism of putting the cart in front of the oxen, but I’ll tell you more about this later.
– No, wait! Firstly you throw the stone in the pond and then you think you’ll leave me without an explanation? Give me at least an example that clarifies what you mean by ideological taxonomy!
– OK. Although I’m glad to hear you, we are on the phone, so I’ll try to summarize my thoughts as much as possible.
There was a time when new genera were created within the Cactaceae family with total confidence on the basis of often weak characters and even using heterogeneous criteria. But how weak they were or how strong these differentiating characters must be to allow the erection of a new genus? You understand that’s not easy, within such a large botanical family, to define some homogeneous and widely accepted criteria. So, we end up with very personal judgements, even today. I think that to discuss about the taxonomic rank of the genus today is equivalent to voluntarily putting oneself fingers into a clamp, so I prefer to discuss about the species rank instead. By this, I don’t want to imply that the concept of biological species is clear, without any dispute and unresolved problems. You’ll get it another time, when we’ll have more chance to reason. But let’s go back to our Cactaceae family. During the mid-sixties of the past century, the forefront of cactology was mainly made by German scholars and the synopsis of the family was contained in C. BACKEBERG’s most important work 'Die Cactaceae'. Quite soon, it became evident that the existence of some genera and species was sometimes scarcely justified, so it became fashionable (a sort of pigeon shooting) to mock the “splitter’s” way of thinking. Finally, the International Organization for Succulent Plant Study (IOS) was created with the purpose of simplifying and stabilizing the nomenclature of the succulent plants (particularly that of the Cactaceae). I’m sure you are aware that the simple fact of meeting with this purpose it’s by itself an ideological operation. Actually, I agree with many of the proposals brought forward by the IOS Cactaceae members and I repute these botanists the most prepared, by formation and often by profession (many are biologist specialized in various disciplines and some in botany). But really I can’t accept the fact that people meet around a table with the aim of ‘simplifying and stabilizing’! I just can’t swallow it! To justify this operation, it was said that the family’s structure was misshaped due to the combined synergy of two effects: the massive presence of enthusiast growers and the interference of nurserymen, a synergy that caused the proliferation of genera, species and varieties. Nobody can deny that these two groups had some effect in the erection of some new genera and new species, but how important this effect has been? Out of curiosity, I have asked myself: how do things go in other botanical families? There are many growers and nurserymen interested in orchids and maybe that’s why the proliferation of genera, species and even lower taxonomic ranks is even higher than in the Cactaceae, but maybe it’s the nature of this family to cause this mess. Among the orchidophiles too there’s a strong debate among splitters and lumpers and the same could be said about mycologists, but I never heard of an organization headed by lumpers. Maybe BACKEBERG and associates have really exaggerated!
– From what you say, I would think yes! You have convinced me, the splitters have created a mess!
– Again out of curiosity, I have browsed some books and calculated the ratio R (species/genera) of some botanical families in alphabetical order. Here’s the result: Agavaceae R = 36; Anacardiaceae R = 7.8; Apocynaceae R = 8.3; Asteraceae R = 22.7; Bignoniaceae R = 7.0; Bombacaceae R = 9.0; Bromeliaceae R = 57; Cactaceae (according to BACKEBERG) R = 9.4. And here I stopped. Why? Because I found a curious thing, as much as three families (Agavaceae, Asteraceae, and Bromeliaceae) show a ratio R (species/genera) definitely higher than that of the Cactaceae, even though they are likely to sustain the same pressure from enthusiasts and nurserymen. Not only, four families have a ratio markedly lower (many genera compared to the species) than that of the Cactaceae, even though, I’d guess, they are much less desirable to collectors. I have then asked myself: why the genus Euphorbia, one of the more sought-after by collectors and nurserymen, hasn’t been divided into many genera, even though it’s made up by a lot of species?
– Are you suggesting, my dear, that somebody has played dirty in order to prevail?
– MARIA, this seems too much to me, generally speaking, but I will soon give you some examples where it would seem that you are at right.