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The genera of Leguminosae-Caesalpinioideae and Swartzieae

L. Watson and M. J. Dallwitz


The following Introduction was prepared with reference to the original Delta package (cf. Watson, 1981; Watson and Dallwitz, 1983), which reflected severe constraints imposed by the computing facilities then available. It has not been re-written to account for editing of the package (see Revision history).


This interactive package is generated from a DELTA database (Dallwitz 1980; Dallwitz, Paine, and Zurcher 1993). It comprises an interactive system for identification and information retrieval using the program Intkey (Dallwitz, Paine, and Zurcher 1995, 2000; running under MS-Windows 95/NT or later), along with descriptions, illustrations, references, and other subsidiary material.

Observations were encoded in the DELTA format (Dallwitz, 1980), and manipulated using the associated programs CONFOR and KEY to generate keys, natural language descriptions and classifications. The DELTA system permits inclusion of ‘comments’, both in the character list (where they are used to qualify state definitions and to provide references) and in the descriptions. This is a most important facility, since any system under which organisms could be described only in terms of a pre-defined character list would lose much valuable information. The comments in the descriptions are not directly available for key-making and classificatory analyses, but they often foreshadow the addition of new characters to the basic list.

The character list (q.v.) includes features of general morphology, seed chemistry and germination, leaf anatomy, wood anatomy, pollen fine structure, cytology, geographical distribution and taxonomic group. Most of the morphological characters are botanically unexceptional and self-explanatory, covering aspects of variation customarily mentioned in descriptions of caesalpinioid genera, plus others which are commonly overlooked such as shoot organization, phyllotaxy and insertion of pinnae. The leaf anatomical characters are also mainly straightforward and easy to observe: they have been discussed and illustrated elsewhere in the course of introducing an earlier version of the character list (Watson 1981). Redundancies in the character list were for convenience in connection with particular operations, or else they reflect the poor quality of some data then available. For example, published descriptions are frequently imprecise about whether or not flowers are bracteolate; therefore, a catch-all character, which is more readily ascertainable from the literature, is also included with a view to its possible usefulness in key-making. The combination of these characters conveys the precise condition obtaining in those genera where 36 is recorded. A similar situation regarding stipules sometimes results in clumsy descriptions. Redundant characters and certain others which have been included with particular applications in mind, should be omitted (masked out) when their use is inappropriate (e.g. for classificatory analyses).

The generic descriptions represent a laborious exercise involving compilation and original observation. The data on leaf anatomy were obtained from leaf sections and epidermal preparations of the species listed in the List of Taxa Studied Anatomically. Most of the material came from herbarium specimens, and some of the characters listed ought to he pursued further in fresh leaves. The data on pollen ultra-structure were provided by A. Graham and G. Barker, while those on cotyledon types are D. L. Smith’s (see Polhill and Raven 1981). Useful information has been lifted wholesale from the new descriptions and keys presented by various authors in Polhill and Raven (1981).

Of necessity, arbitrary or pragmatic decisions were taken with regard to inclusion of genera. However, all the genera accepted in Polhill and Raven (1981) are described, except in the Cassieae. Cassia is represented by a description of the genus sensu lato, rather than by Cassia sensu stricto, Senna and Chamaecrista as advocated by Irwin and Barneby. This does not imply rejection of Irwin and Barneby’s taxonomic conclusions, merely unavailability of detailed descriptions. Should it seem desirable, the character list and the data could in future be edited to accommodate them. By contrast, the genus Bauhinia is represented by two descriptions: the one sensu lato (which is probably preferable; cf. Wunderlin and Larsen 1981), the other sensu stricto and admitting recognition of the segregate genera Barklya, Bracteolanthus, Gigasiphon, Lasiobema, Lysiphyllum, Phanera and Piliostigma (also included, but scarcely separable and of dubious taxonomic value). The Swartzieae (Aldina, Baphiopsis, Bocoa, Candolleodendron, Cordyla, Exostyles, Harleyodendron, Lecointea, Mildbraediodendron, Swartzia, Zollernia, and Holocalyx are included, not to incur the wrath of Cowan and Polhill (1981), who regard them as Papilionoideae, but mainly because comparative descriptions have been prepared and it seems a pity not to make them available. In any case, the family Leguminosae still needs comprehensive taxonomic reassessment in terms of across-the-board samples and fully comparative data. Such an operation could throw a new light on the classification of genera currently referred to the subfamily Caesalpinioideae, and until it has been undertaken it would he unwise to assume that the Swartzieae have found their final resting place.

The original aim was to prepare comprehensive, properly comparative descriptions of the genera, incorporating all the information necessary to conduct classificatory analyses and to prepare workable printed keys (cf. Watson 1981). The DELTA system was not available until quite late in the development of this database. Consequently, the character list was ill designed to take full advantage of the facilities now offered, and in the earlier stages of data-gathering a great deal of useful information, which would now be recorded as ‘comments’, was lost. Nevertheless, in the context of Caesalpinioideae, the character list is now very comprehensive by any standards, and most of the genera are quite thoroughly recorded against it. The database is adequate for producing conventional keys which are practical, and which work so far as they have been tested (see Watson and Dallwitz, 1983), and a coherent classificatory picture has emerged (cf. Classification). Nevertheless, there is infinite scope for further refinement and development, and much information of a quite elementary kind is still lacking. Some genera have been studied anatomically scarcely or not at all (including Amherstia, Apaloxylon, Augouardia, Bathieaea, Brenniera, Ceratonia, Lemuropisum, Mendoravea, Thylacanthus, Umtiza, Zenia), and many large genera are recorded for the more esoteric characters on the basis of only one or a few species.