In this article Bruce Bayer responds to the notion that apparent leaf twist arrangement is a defining characteristic and further explains his disagreement in recognizing the Buffeljags plants as a new species. (Also see Haworthia flowers – some comments as a character source, Volume 7, Chapter 4:- What is typical Haworthia mutica?, and Volume 7, Chapter 2:- Further exploration in Haworthia. Further to finale.) The species definition Bayer uses is that populations are fractal and DNA is governed by mathematical non-linearity. What does that mean? We have space with two dimensions latitude and longitude, and we have time with two dimensions – calendar time, and the speed (instability) of the arrangement of the DNA base pairs. At any moment in linear calendar time there will be an arrangement of the DNA depending on the stability of the DNA. At one time there will be a clear set of ‘species’ and at another time a different set as the mix of characteristics continually change within and between the populations. ~ Lawrence Loucka
Haworthia mutica (groenewaldii) and its twisted leaves.
By M.B. Bayer
There is some argument about the status of this population of plants at Buffeljags. I have explained my opinion of it based on a species definition that I use. I also have reported on three other populations a short way away at Rotterdam. Furthermore I have discussed the flowers at length in a flower report. These are all available free on Haworthiaupdates.org. Gerhard Marx does not agree. The disagreement first has its roots in what constitutes a species and Marx stays with the standard view that characters are what define species. I opt for the view that species are systems related to geographic distribution and to all the elements that drive vegetation and change (evolution + equals change from some unknown initial condition). I think these patterns of change and difference are fractal i.e. detailed pattern repeating itself. Perhaps it would be more correct to say that the organization of pattern is according to a mathematical function which is non-linear. This means that the end product has many different outcomes. But this is complexity just of argument that none of us can deal with.
What comes into the geographic nature of species is also the nature of habitat. What happens is that we have a set of apparent species in Haworthia with a known distribution range. These species are primarily H. retusa and H. mirabilis. There is clear evidence that H. pygmaea and H. mutica emerge from a milieu of populations of those two and that H. floribunda is also involved. Buffeljags is geographically central to this arrangement and the habitat (wrongly described in the description of H. groenewaldii) is very unlike those where the named species generally occur. It is thus no surprise that the plants appear different. The Buffeljags population and its habitat also differ to a small degree from the west side of the river, but both are essentially geologically fairly recent river alluvial deposit.
Marx is insistent that the plants at Buffeljags are so different as to be a discrete species and I disagree. My disagreement is based on my experience of characters in plants. In Haworthia I think these are few and obscure. Thus it is almost impossible to delineate or circumscribe a species by characters and no one has succeeded in producing an identification key that can work. All the differences of opinion and argumentation about names come down to this issue of a species definition and the characters available to recognize them.
The essential points made for H. groenewaldii as a species is the shiny leaf surface and the flowering time. H. mutica does flower four months earlier – agreed. But H. marginata in the same close area also flowers similarly out of synchronicity with H. marginata elsewhere, as H. minima was also observed to do. In elaborating differences for H. groenewaldii, Marx offered the facts that the plants had fish-tail buds and that H. mutica did not. Very soon after he stated that he did not actually know what the case was in H. mutica.
Fig. 1 to 9, MBB7801 Haworthia mutica (groenewaldii), Buffeljags.
In addition he maintained that the leaves in H. groenewaldii were different as follows…”In terms of the angled newer leaves of H. groenewaldii, have a look at the plants again and you’ll see the young leaves are consistently twisted sideways. A spiraling effect. This never shows up in H. mutica”. I find this statement very odd because such a structural difference would come down to a difference on the level of genus or even family. So I looked at the plants I have in my possession and provide illustrations here to demonstrate no significant deviation in respect of twisting. I have even included a picture of a mature plant (fig. 10) of H. mirabilis to show the same “character”. The spiralling effect is universal in the aloids and is even visible in those species with distichous leaves. In the retusoids, where H. mutica belongs, the leaves have been said to be 5-farious. More usually it is possible to see them as trifarious. In young seedlings the leaves are bifarious as the very basic spiral effect comes into play.
I do not think this is a character one can use to distinguish a species at all. There are many cases where it is fairly possible to characterize populations by a wide range of so-called characters. My opinion is that generally in the many species (by my definition) of Haworthia this can virtually only be done at individual plant level. The Buffeljags and Rotterdam populations are simply the western counterparts of populations around Albertinia (eg H. mirabilis ‘splendens’, H. pygmaea ‘fusca’, H. pygmaea ‘esterhuizenii’) that emanate from the relationship of the prime species that I named above.