Position, (Botanical Museum and Herbarium, Utrecht) Played An

Remarks on the position, the delimitation and the subdivision of the Rubiaceae C.E.B. Bremekamp (Botanical Museum and Herbarium, Utrecht) (received October 22nd, 1965) Introduction It is often assumed that the delimitation and the subdivision of the various families which have been distinguished in the Angiosperms, do no longer offer serious difficulties. They would belong to those objects of study for which already long ago a fairly satisfactory solution was found. If we wish to be acquainted with this solution, the would have would be look such works only thing we to do, to up as Bentham and Hooker’s “Genera Plantarum” and Engler and Prantl’s “Natürliche Pflanzenfamilien”. Some improvements might still be desirable, but these would be of minor importance only. These as- sumptions, however, are to be regarded as dangerous illusions. That the serious of the found in very nature shortcomings the delimitation and subdivision of these families, especially of the larger is is ones, so often overlooked, apparently due to an attitude of mind which is observed in a comparatively large part of the taxonomists, viz. lack in the a of interest development of a truly natural classification. This is not incomprehensible. Most of them spend the major part of their time in the elaboration of floras covering areas of more and or less limited extent, they are but rarely aware of the fact that the of the families which is obtained in this remains knowledge way, necessarily incomplete. Moreover, in the elaboration of a flora the most essential point is the construction of serviceable keys to the species as well as to the groups of higher rank, not the exact deli- of the latter end mitation these groups: to usually more material is has required than the compiler of a flora at his disposition. However, we must not overlook the fact that a key, in order to be serviceable, need not reflect the degree of affinity between the units with which it is dealing; in reality, such keys are often entirely or almost entirely artificial, and this applies therefore also to classifications which are I discuss based on such keys. To illustrate this, will here some of the characters by the aid of which in the Rubiaceae very suitable keys have been but which when subse- to the genera constructed, they quently were used for the elaboration of a classification, led to entirely unsatisfactory results. To the characters which for a long time have played an important in the subdivision of the the either part Rubiaceae, belong presence of uni- of their kind of which or pluriovular ovary cells, fruits, to 1 2 C. E. B. BREMEKAMP this end divided in and and were dry fleshy ones, the nature of their seeds, of which also two kinds were distinguished, viz. winged and ones. even a of the that wingless However, superficial study groups have been distinguished by the aid of these characters, will show that the most of them are entirely unnatural. As differences are morpho- of this have been logically hardly any value, might expected. The number of ovules cell shows continuous of per ovary a range there variation, and so long as is no reason to assume a correlation between a definite number ofovules and one or more other characters, it is therefore not justified to attach to the presence of one or two ovules cell taxonomic value than that of per ovary a greater to three that or of another number of them; we know, in fact, the number of ovules cell within the limits of per ovary may vary a single genus of the (see my “Monograph genus Pavetta L” in Fedde, Repertorium 37: 10. and remarks the Anotis DC 1943, my on genus and the Cruckshanksieae in the last of the chapter present publication) as well in that account of their features as genera on many common are to be as so in Tarenna Gaertn. and Pavetta L regarded nearly related, e.g. (see p. 7 of my “Monograph of the genus Pavetta L”). the That difference between dry fruits and fleshy ones can not be used for the characterization of natural is also groups easily com- This distinction is an not a prehensible. ecological, morphological one, and in both kinds of fruits quite considerable morphological differences are found; in some instances the differences between a dry and fruit a fleshy may even be smaller than those between two kinds of fruits two kinds of In the dry or fleshy ones. genus Mussaenda L species with dry fruits are found side by side with species producing if fleshy ones; even these species are divided over two genera, as sometimes is done, this does not make much difference, for in that case we will have to admit that the two kinds of fruits are found in related very nearly genera. The same applies to the distinction between winged and wingless seeds: this too is an ecological, not a morphological distinction. From the morphological point of view these wings are by no means all alike; in the the tribe in which the with seeds Cinchoneae, genera winged were are in the which be brought together, they genera may rightly regarded as near allies of Cinchona L, in position as well as in the structure of the cells of which they are mainly composed, entirely different from those that are found in the genera which were trans- ferred by me to the Rubioideae. Another drawback of the classifications accepted in the works mentioned above, is that they are based mainly on earlier classifications which drawn when much smaller number of were up a genera were known, and that the authors often assumed that the subfamilies and even the tribes based on this more limited number would suffice for the of the discovered This incorporation subsequently genera. ap- is the of the fact that so often has been parently explanation a genus into tribe into which it does fit. In the of the squeezed a not case Rubiaceae there number of of which it is are even quite a genera POSITION, DELIMITATION AND SUBDIVISION OF THE RUBIACEAE 3 extremely doubtful whether they really belong to this family. This point will be discussed in the second chapter. Many taxonomists, moreover, seem to feel a certain reluctance to accept subfamilies which contain but a single tribe, and tribes which contain but a single genus. This reluctance, however, is entirely unjustified. We know several families and even some orders which contain but a or small number of and there is single a very genera, accordingly no reason whatever for assuming that a subfamily or a tribe should contain than of the always more one group next lower is rank. Whether a taxon to be classified as a subfamily or a tribe number evidently depends upon the and the importance of the charac- it ters in which differs from its nearest allies and on nothing else, and the where our predecessors haveoverlooked presence of some differences or undervalued theirimportance, it is doubtlessour duty to correct them. With regard to what has been said in the preceding paragraph, it is, of course, of importance to find ways and means for estimating the taxonomic value of the of groups characters that are to be used for the distinction of the tribes and subfamilies and, naturally, of the families too. In the case of the latter the number of diagnostic characters is often extremely small and their value not rarely dubious. With regard to the Rubiaceae this point will be dealt with in the chapters one and two, but at this point it is perhaps worth while to draw the attention to the fact that in the description of this family given in do the works mentioned above we not find a single character that be This of can regarded as a truly general one. is, course, due to the fact that this family, in the delimitation accepted in these works, comprises elements which do not really belong to it. The inclusion of such has often led elements, moreover, to entirely false conclusions with regard to the affinity of the families. In the case ofthe Rubiaceae, for the inclusion of the Bth. instance, genera Henriquezia Spruce ex and Platycarpum Humb. et Bonpl. has led to the assumption that there should be a comparatively close affinity between this family and the when these two it Bignoniaceae. However, genera are excluded, ap- pears that not a single argument is left which might possibly be adduced in favour of this view. After the exclusion of the genera Carlemannia Bth. and Sylvianthus Hook. f. the affinity with the Capri- and their allies has become less and if the foliaceae pronounced, genus Dialypetalanthus Kuhlm. had been left in the Rubiaceae, this would have been a good argument for assuming a rather close affinity with the ! It of Myrtales is therefore great importance that such misclassifications are corrected. Several other of which examples genera were incorpo- rated in the Rubiaceae on insufficients ground, will be given in the chapter dealing with the delimitation of the family. of It can, course, not be denied that the number of characters which related taxa have in decreases common, with the increase in rank of the taxon to which they belong; it is certainly no wonder families that have, as a rule, but a very small number of general characters. However, groups based on a single general character should always be regarded with some distrust. 4 C. E. B. BREMEKAMP Verdcourt (Bull. Jard. hot. de 1’fitat, Bruxelles 28: 228.

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