Paleobotanical Taxonomy and Nomenclature: the Need for a New Approach Author(S): S

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Paleobotanical Taxonomy and Nomenclature: The Need for a New Approach Author(s): S. V. Meyen Source: Taxon, Vol. 24, No. 1 (Feb., 1975), pp. 251-254 Published by: International Association for Plant Taxonomy (IAPT) Stable URL: http://www.jstor.org/stable/1219049 . Accessed: 13/04/2014 09:44

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This content downloaded from 212.238.43.46 on Sun, 13 Apr 2014 09:44:18 AM All use subject to JSTOR Terms and Conditions names as validly published, cannot logically be defended. Therefore, proposals 41 and 42 (Petersen, Taxon 23(4): 657. 1974), dealing with vernacular terminations, although not referring to family names, should also be rejected.

Proposal 53: This is a definite improvement over the present wording. It helps to eliminate questions which at various times have been put in writing to the secretary of this subcommittee.

Summary: The Subcommittee for Family Names recommends adoption of Proposal no. 53 and referral of Proposal no. 18 to a panel of linguistic experts; on the other hand, it does not recommend the adoption of the following proposals: without no. (Paclt), 16-17, 39-40. GiuNTHER BUCHHEIM, secretary

PALEOBOTANICAL TAXONOMY AND NOMENCLATURE: THE NEED FOR A NEW APPROACH*

S. V. Meyen**

Summary The failure of paleobotanists to appreciate parallelism and character-variation in their materials underlies the present confusion and instability of paleobotanical classification and nomenclature. On the other hand, application of the Code in its present form does not bring about stability either, and rewording of part of Art. 3 is proposed.

Taxa of fossil plants should be recognized on the basis of the totality of our knowledge of whole organisms, rather than on one or the other of their parts. Moreover, only those characteristics that can be demonstrated by actual petrifactions or impressions should be used in delimiting taxa, rather than hypothetical data derived by extrapolation from such remains. The most ideal classification will recognize taxa that are further elucidated by subsequent research and new data, rather than constantly modified totally or to a major extent by the new evidence. To achieve these objectives we need, at various stages, both "artificial" and "natural" classificatory schemes, the first gradually giving way to the second as more facts become known and the totality of the taxa is better understood. The degree of "naturalness' or "artificiality" of plant taxa, whether fossil or Recent is highly subjective and even with a very complete understanding of a group, subjective judgement still plays a role and we must admit that a truly "natural" classification is illusory. So, for various reasons, we produce and accept compromises as we delimit taxa. Moreover, the discontinuities recognized in a multi-taxon spectrum with strong clinal characteristics vary greatly in relation to the experience of the taxonomist, the purposes for his classification, and especially his preconceptions concerning the group. Of course, unlike extant plant taxonomy, where potentially most of the pertinent data are available or attainable, paleobotanists necessarily work with only bits of the record. A classification based on an incomplete knowledge of the fossil plant can be termed "formal" [artificial] and the taxa involved, "form-taxa". Inasmuch as no taxon, living or fossil, can be known totally, all classification has such a "formal" quality, to one degree or another. The extent of formalness or of naturalness is itself a cline, the points along which are entirely subjectively determined and relative.

* Abbreviated version of a more detailed paper which could not be published because of its length. Xerox copies of the original paper (typescript) are available, upon request, from the Editor of Taxon. [Ed.]. This paper was received on time and could not be printed earlier for technical reasons. The rapporteurs request the Committee for Fossil plants to study the proposals and to report at Leningrad. ** Geological Institute of the USSR Academy of Sciences, Pyzhevsky per. 7, 109017 Moscow-17, USSR.

FEBRUARY 1975 251

This content downloaded from 212.238.43.46 on Sun, 13 Apr 2014 09:44:18 AM All use subject to JSTOR Terms and Conditions In the present discussion of classification, I have purposefully omitted "phylogenetic" ones, because I do not believe that such classifications exist, at least not in botany. For example, it is often assumed that coniferophytes are phyletically related to progym- nosperms, but whether these taxa were connected directly or through the cordaitalean complex, or some other unrecognized groups, we are entirely ignorant. In studies of Recent groups, taxonomists distinguish the constituent taxa and then arrange them in a linear, "phylogenetic" sequence. But in many cases, paleobotanical data obtained later have negated such "phylogenies", and yet they have continued to be used. Although construction of phylogenetic hypotheses never loses its fascination, we have no right to mix speculation with factual information without clearly identifying that which is speculative from the hard facts derived from correct observations of specimens. A fuller discussion of the phylogenetic approach in systematics is given by Lubischew (1963, 1968). From the very beginnings of paleobotany, classifications have been constructed on the basis of fragments, plus very considerable conjecture about the missing parts, the latter usually derived from studies of what appeared to be analogous structures in better- known plants. In the last century, paleobotanists encountered fossil leaves indistinguishable from those of ferns but lacking the sporangia ferns should have. Later on, anatomical data suggested a possible cycadalean relationship but then remains with organic connection to seeds were discovered and pteridosperms were recognized. Thereafter, when fern-like leaves were found without sporangia, paleobotanists assumed they were seed-ferns. To our surpise we now discover that some of these are true ferns and the circle has been completed! This sort of taxonomic confusion is a part of the history of a great many fossil taxa. There are two principal causes of such errors in judgement which are so common in paleobotany: (i) Unwarranted extrapolations from the meagre data usually available to paleobotanists in reconstructing the entire plants on the basis of conventional coordination of parts ["extrapolation of habitual correlations"]; that is, if one morphological condition is evident, then other conclusions are made about the morphology of the plant on pure speculation by comparison with other "similar" plants, Recent or fossil. (2) Biased assumptions about the affinity of fossil plants based on one or a very few characters that are considered to be invariably diagnostic of the particular group. Of the first sort of logical error, I have already written above and elsewhere. The second is especially well-illustrated by glossopterid leaves, the majority of which do have simple leaves with netted venation. However, this does not mean that all glossopterid leaves were simple and net-veined nor does it follow that all simple leaves with netted venation must be assigned to this group. In fact, there are data indicating that some glossopterids had simple or pinnate leaves and closed or open venation. I refer to this assumed uniformity of characters of a group as "unjustified homogenization". These two kinds of logical errors rarely occur in a pure state but more often together in various proportions. The first type produces taxa that are unduly heterogeneous because of the inclusion of discordant elements; the second type of error results in unnaturally homogeneous taxa because they are recognized in ignorance, or in disregard, of normal biological variability of characteristics. Together, these faults of logic, plus normal observational mistakes, have produced chaos in paleobotanical classification and nomenclature. And the problem is further compounded by paleobotanists studying relatively few organisms in a single geographical area. For example, some one studying the Upper Palaeozoic in Siberia deals with leaves which are superficially similar to the European Cordaites, the only suitable group apparently to which the Siberian leaf remains may be assigned. But associated fructifications prove that the leaves from the two continents are really quite distinct and the assumption that European and Siberian cordaitalean leaves belong to a common family, or even a common order, is at least poorly founded! There are many examples of these and related problems, as well as the philosphical bases for attempting to solve them, which I have written about elsewhere (I970b, I97I-d, and in press) but I would also refer those most concerned to Krenke ('933-35) and to Urmantsev (I970, I972). Always difficult, the concept of what constitutes a genus is unquestionably most

252 TAXON VOLUME 24

This content downloaded from 212.238.43.46 on Sun, 13 Apr 2014 09:44:18 AM All use subject to JSTOR Terms and Conditions perplexing among those studying fossil plants. This is true because before preservation occurred, the individual plants disintegrated into few to many parts (which will be called "organs" hereinafter) whose original interconnections are partly or altogether unknown. The situation is further complicated by the fact that we usually have such a small sample of the whole plant. Because of parallelism, what seem to be very similar or even identical organs may, in fact represent different genera, families, or orders. At the same time, the range of variation in any organ of a single genus generally remains unknown. These peculiarities of paleobotanical taxonomy were recognized by Ad. Brongniart who introduced the now universally adopted standards for the study of fossil plants. Realizing that the organs of a plant are usually unassociated, he introduced an independent nomenclature for different plant organs, even though they may have come from the same plant originally. His views and their impact on paleobotany have been thoroughly analyzed by Stafleu (I966, 1967; see also Faegri, 1963). Recognition of organ- genera, form-genera, and their introduction into the Botanical Code logically capped Brongniart's contributions to paleobotany. In the Stockholm and Paris versions of the Code, the concepts of "form-genus" and "organ-genus" were described but not defined. Article PB. i contained two notes: the first sanctioned the use of separate generic names for different modes of preservation; the second note proposed practical criteria for recognizing organ- and form- genera. The ambiguity, even logical inconsistency, of these "definitions" was properly criticized by Faegri (I963). The Montreal Code went further toward delimitation of these concepts by stating that an organ-genus is assignable to a family while a form-genus is not, but this "solution" has been criticized (Faegri, 1963; Stafleu, 1967; Krassilov, 1967, 1969a; Meyen, I97ob, 1971a, d). It is also important to note that the Montreal Code lacks a clear reference to form-genus, a concept that originated with Brongniart more than a century ago. The Seattle Code preserves the Montreal approach. It now seems desirable to revert to the more flexible definitions of the Paris Code but to make them more complete and logically consistent. If my proposed improvements (see below) are adopted, it will be seen that, depending on the situation, a paleobotanical genus may be organ- and form-genus at the same time. For example, Lycospora will be an organ-genus in relation to Lepidostrobus and a form-genus in relation to Densosporites. In the present ICBN, both kinds of genera are treated as if they are separate, independent categories within which the affinity of all the species of a genus to a particular family are equally well-established. On the contrary, we know that often the affinity of only one of the constituent species is known; similarly, different species commonly referred to a single genus may be representatives of different families. One can easily imagine or find actual examples in the literature demonstrating that when the affinity of a genus is unproven, the present provisions of the ICBN do not contribute to the nomenclatural stability of fossil plants. Moreover, if we follow the Code strictly, there would be no organ-genera because it does not define what is meant by "the genus is assignable to a family" or how one should go about such an assignment. To resolve the confusion that exists in the present Code, I propose to reword the Note in Art. 3 as follows: I52. "Names of species and consequently of higher taxa of fossil plants are usually based on fragments, whose mutual connection can be rarely proved. Accordingly they cannot be classified in the same way as entire plants. Therefore it is permissible to introduce generic names (organ-genera) for different parts (organs) of the plant body and for different modes of preservation of the same part. It is also admissible to introduce a common generic name (form-genus) for morphologically uniform fragments, although they have been parts of plants of quite different taxa. Any generic name of a fossil plant may represent either an organ- or a form-genus: It will be an organ-genus when considered in relation to other generic names introduced for parts (organs) of different morphological nature or type of preservation; but it will be a fom-genus when considered in relation to generic names introduced for parts (organs) of the same morphological nature or type of preservation. Establishment of organic connection of two or more organ-genera does not mean, necessarily, that one or other need be abolished. Example: Genus Lycospora J. M. Schopf, Wilson et Bentall (established on miospores)

FEBRUARY 1975 253

This content downloaded from 212.238.43.46 on Sun, 13 Apr 2014 09:44:18 AM All use subject to JSTOR Terms and Conditions is an organ-genus in relation to the genus Lepidostrobus Brongniart (established on strobili), but is a form-genus in relation to genus Densosporites (Berry) Butterworth et al. (also established on miospores)". To complete the discussion on the genus problem in paleobotany, we should touch on the matter of generic names for reconstructed plants. It seems reasonable to adopt Krassilov's (i969b) proposal. He suggested the use of the name of one of the organ- genera of the plant reconstruction, and, for the sake of exactness, to append to the generic name the term "restitutio" (abb. "rest.") together with the author's name and date of the reconstruction; e.g. Nilssonia Brongniart I825, rest. Harris 1941 (= Nilssonia + Beania + Androstrobus). Krassilov's paper, incidently, reviews fully the methods for the reconstruction of fossil plant life forms. There are also many difficulties in treating suprageneric taxa in paleobotany but these are somewhat different and I will consider them in another paper.

References

FAEGRI,K. 1963 - Organ and form genera: significance and nomenclatural treatment. Taxon 12: 20-28. KRASSILOV,V. A. 1967 - On classification of organs of older plants. In: Tesisy dokladov k XIII sess. Vsesojuzn. Paleontol. Obsch. Leningrad (p. 14-34) (in Russian). KRASSILOV, V. A. I969a - On the definition of the palaeobotanical taxa form-genus and organ-genus. Palaeontol. J. 2: 125-126 (in Russian). KRASSILOV, V. A. I969b - On the reconstruction of fossil plants. Palaeontol. J. 1: 3-12 (in Russian). KRENKE,N. P. 1933-1935 - Somatische Indikatoren und Faktoren der Formbildung. In: Phinogenetische Variabilitit, Abh. Abt. fiir Phytomorphogenese, Inst. fiir Biol., I. Bd. Moskau (p. 11-415) (in Russian, German Summary). LUBISCHEW, A. A. 1963 - On some contradictions in general taxonomy and evolution. Evolution 17: 414-430. LUBISCHEW, A. A. 1968 - Problems of systematics. In: Vorontsov, N.N. (ed.). Problems of evolution, Novosibirsk (p. 7-29) (in Russian, English summary). MEYEN, S. V. 1968 - On the procedure of investigating and describing fossil plants. Palaeontol. J. 3: 103-112 (in Russian) MEYEN, S. V. I970a - Epidermisuntersuchungen an permischen Landplfanzen des An- garagebietes. Paldiontol. Abh. 3B: 523-552. MEYEN, S. V. I97ob - Some theoretical problems of modern palaeobotany. Palaeontol. J. 4: 3-15 (in Russian). MEYEN, S. V. I97Ia - Genus concept in palaeobotany. III Inst. Palynol. Conf., Paper for plenary Session, Novosibirsk. MEYEN, S. V. I97Ib - Modern palaeobotany and theory of evolution. Priroda 2: 48-57 (in Russian). MEYEN, S. V. I97Ic - Parallelism and its significance for the systematics of fossil plants. Geophytology 1: 34-47. MEYEN, S. V. I97Id - Phyllotheca-like plants from the Upper Palaeozoic flora of Angaraland. Palaeontographica I33B: 1-33. MEYEN, S. V. (in press) - Plant morphology in its nomothetical aspect. Bot. Rev. MEYEN, S. V. 1969 - Epidermal studies of Angara Callipteris and Compsopteris. Trudy Geol. Inst. Acad. Nauk SSSR 19o: 59-84 (in Russian). STAFLEU,F. A. 1966 - Brongniart's "Histoire des veg6taux fossiles." Taxon 15: 320-324- STAFLEU,F. A. 1967 - Palynology, nomenclature and terminology. Rev. Palaeobot. Palynol. 3: I5-26. URMANTSEV, Y. A. 1970 - Isomery in living nature. I. Theory. Bot. J. 55: 153-169 (in Russian, English summary). URMANTSEV, Y. A. 1972 - An attempt of axiomatic construction of the General System Theory. In: Systems Research, Yearbook 1971. Moscow (p. 128-152) (in Russian).

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