The Journal of Indian Botany/Volume 1/December 1919/On the use of the term "Variety" in Systematics.
ON THE USE OF THE TERM "VARIETY"
IN SYSTEMATICS.
BY
L. J. Sedgwick, F.L.S.
The remarks which follow are based on practical experience as a field worker only, and the writer hopes that readers of the Journal will accept this limitation when considering them. The main questions brought up for discussion are : (l) whether the term variety as used in our Floras is applied to one natural phenomenon only, or at the worst to several phenomena which are perfectly homologous, and if not, then (2) whether there is any way of separating out the various phenomena hitherto confused under the one term, and assigning to each a separate term ; since it is clearly unscientific to use one and the same term for phenomena which are heterologous.
It is usually assumed that in all taxonomic work the personal equation enters largely, and cannot be eliminated. It is open to question whether the latter part of this assumption is correct so far as species and units lower than the species are concerned. So far as concerns genera, families and all units above the species, since these taxonomic divisions are based on assumed descent, and since for the descent of plants our only material is the very fragmentary palasontological record, it is clear that our results must largely depend upon guess work. And it is for that reason that the tendency of even our deepest systematic thinkers to allow their generic divisions to be (sometimes at any rate) influenced by considerations of convenience is a comparatively venial sin. In the case of species however and all intra-specific units—excluding of course extinct species—there is no possibility of pleading lack of evidence. If into our discrimination of species the personal equation enters the fault is ours. We are hampered by weakness of power of perception, by shortage of workers, by lack of time, and by idiosyncrasies that could be eliminated. But the truths are there if we could only unravel them. In the case of most "critical" species the number of available individuals is legion. Mendelian and other experiments could be carried out. Even if the species or group of species is in an active state of evolution at the moment its different forms and developmental tendencies could be enumerated and charted. For instance, to take an imaginary case of an Indian genus believed to be in an active condition of evolution, if the State cared to engage 100 trained observers to collect, observe and measure, and 10 trained systematists to examine and collate results for five years, facts would emerge at the end which would establish, at any rate for the time being, the limits of species and lower units and their developmental tendencies. The writer is not for a moment advocating such a course of action as a practical way of spending the State finances! The illustration is merely given by way of showing that so long as the evidence is completely available no problem is absolutely beyond solution. In short, where we find in the floras so-called "critical species" their critical character is duo to human infirmity, and is not absolute.
Generally speaking all Indian workers seem to find that where the Flora of British India gives many varieties a mixture of species may be suspected, which patient collecting and collection of material will (and as a fact often does) clear up. Conversely it must be admitted that some species in the Floras can be broken down by patient collection of transitional series. Those two facts would go a long way towards establishing the truth of the proposition enunciated in the preceding paragraph. But unfortunately, partly owing to post-Linnasan and especially modern Mendelian researches into the origin of species, and partly owing to the extremely minute examination to which certain particular genera have been subjected in the West, and the recognition thereby of numerous intra-specific forms, there has been of late years a strong tendency to cast scorn upon Systematics, and even to take the final step of asserting that the individual is the only ultimate unit. Fortunately, however, both the economist who obtains products from plants and the field-worker who observes and collects them, know that the individual is only the unit in the same sense that no two members of one nation or even of one household are exactly alike, and that just as human beings can be and must be grouped into larger units on various scientific and social basses, so among plants there are units containing millions—often countless millions—of individuals, whose common characters can and must be described, and to which the application of a "barbarous binomial" is both convenient and necessary.
The unit commonly accepted and used for more that a century and a half is the Linnaean species. And it is this particular unit upon which soma students of genetics to-day seem to cast such scorn, regarding it as an erroneous conception and no true phenomenon. Now this view is one which the writer believes to be wrong. The practical field-worker knows that in a region with which he is familiar he can at once assign to their Linnaean species all but au infinitesimal fraction of the plants that he sees around him. Of that fraction many are simply freaks or sports ; and as there is a tendency for such freaks to he collected and to find their way into herbaria it follows that herbaria may often give an exaggerated impression of the range of variability of species generally. Into the genetic phenomenon of freaks this paper cannot enter.
Over and above freaks we have to recognize a number of other types of variability.
First there is the phenomenon of geographical change, which may be either gradual or sudden. As an example of the first, the colour of the spikelets of many Cyperacece and GraminecB is paler in North India and gradually darkens as one goes south, until on the Nilgiris it is almost black. As an example of the second, Ageratum conysoides Linn, is on the Nilgiris a delicate-stemmed plant with pure mauve flowers, while in the Dharwar District of the Bombay Presidency it is a coarse-stemmed and coarse-leaved plant with dirty white flowers. The causes of geographical change are very obscure. Complex climatic factors have to be reckoned with, as well as geological formations. There is also the phenomenon of isolation of "lines," which are discussed below.
Secondly there is a type of variability of a purely edaphic character within the same geographical region. Thus Flueggea hucopyros Willd. would seem to be merely an edaphic (xerophytic) form of F. microcarpa Bl.; Leucas Montana Sr. would seem to be the xerophytic form of L. mollissima Wall. Ihe various edaphic forms of many species not hitherto split off by the Floras are well known.
Thirdly there are distinct cases of variability in life-period. Thus Fimbristylis diphylla Vahl., a perennial, has an annual form var. annua (sp.) R. and S. : and similarly Cypents Iria L. (see p. 693 of Journ. Bom. Nat. Hist. Soc. Vol. XXV No. 4). Cypcrus fiavidus Retz. would seem to be only an annual form of C. Haspan L.
Fourthly there would seem to be plants which exhibit a sort of seasonal dimorphism, not of course homologous with the same phenomenon in insects. Thus some species of Smithia have small flowers when they mature in the rains and large ones when they mature in the dry weather. S- flava Dalz. (var. in Cooke. F. Bom. Pres.), if not a valid species is apparently a seasonal form of S. sensltiva Ait. ; while last winter the writer found at Yellapur in North Kanara a plant which corresponded exactly with S. bigemina Dalz. except that it was much larger in all its parts especially the flowers, and had matured in the winter instead of the rainy season.
Fifthly there is the much more difficult phenomenon of "lines". That these are due to the interplay of Mendelian characters is now apparently established. As said above; geographical changes of an abrupt type are probably caused by isolation of lines. The result of isolating lines is well seen in the cultivated cereals. In natural conditions isolation is much less frequent; in fact it would not be too much to say that Nature abhors a pure line, just as she abhors the inter-specific cross. And it is these two facts alone which secure the stability and continuity of the Linna^an species. Nevertheless varieties due to isolation of lines without geographical isolation almost certainly do occur,—for instance Scirdus supinus var. uniondis Cke, and Cyperus lria var. panicifonais Cke.
Sixthly there are the not infrequent cases of species and genera which are in an active state of evolution, producing a maze of forms among which clear specific lines of demarcation are not discernible. These forms may be the De Vriesian mutants. It would be beyond the scope of this paper to discuss this point; but it is necessary for the argument to say that whereas "lines" seem to be the product of isolation and combination of already existing, stable allelomorphs, the changing evolutionary forms now referred to would seem to be caused by instability of the allelomorphs themselves, which in such cases are disappearing and reappearing with changed properties.
Seventhly (although they stand on quite a different footing) it is necessary to refer to interspecific hybrids, which though normally abhorred by Nature, do occur, and will ultimately be detected in India as they have been in Europe.
Now, omitting hybrids, our floras have for the most part in the past called all these varied forms of whatever origin by the one word variety. It is true that in cases of species with a very great range of variability the forms have sometimes not been given a varietal name, but simply listed under numbers or letters. But it would appear that this has been due more to convenience than to a clear discernment of the different phenomena.
Before considering the use of terms for units below the species it is desirable to consider whether we are justified in using the same term "species", undifferentiated, for the Linnaean group of individuals in which the allelomorphs are stable as well as for those in which they are unstable. The writer would suggest that the two phenomena be distinguished as "species (constaus)", and "species inconstans", omitting in practice the word constans.
For units below the species the following scheme is suggested:—
A. For freaks or sports no special term, each one to be separately described.
B. (1) For geographical forms, where sharply distinguishable, the trinomial system now used by ornithologists. (2) For edaphic forms the term varietas followed by the ordinary ecological term such as ophytica halophytica, etc.
(3) For life-period forms varietas annua, biennia, etc.
(4) For seasonal forms varietas hyemalis, aestivalis, etc.
(5) For "lines" varietas Mendeliana followed by the letters of the Greek alphabet.
(6) For forms of inconstant species forma is the ultimate unit, to be grouped about recognizable lines of evolution in various ways. For this case it is not possible to suggest hard and fast rules. The study of these inconstant species is a special one, for which the name micro-systematics might be used. A good many European and American genera have been studied in minute detail, and recently Ammannia and Rotala in India by Blatter and Hallberg in Journ. Bom. Nat. Hist Soc.
C. For hybrids the usual multiplication sign.
It will be argued that we do not know which variant forms are to be assigned to which class in the above scheme. And this is true. But temporary ignorance is no valid excuse for continuing to confuse under one term phenomena which are not homologous. Gradually the truth will emerge.