Centrosema pubescens is now Centrosema molle

During the last 2 or 3 decades, agronomists and zootechnists who work with tropical forages have had to endure a series of changes in the scientific nomenclature of these plants. Some of us can remember back to when reference to a forage was like an exercise in spelling (e.g., Stylosanthes guyanensis became S. guianensis); or a taxonomic exercise in determining species (e.g., the forage grass 'Guatemala' was once Tripsacum laxum and is now T. andersonii), genera (e.g., Cassia rotundifolia became Chamaecrista rotundifolia), and even both genera and species (e.g., perennial soybean was first Glycine javanica, then G. wightii, before becoming Neonotonia wightii). Although we might have occasionally felt uncomfortable, in the end, we accepted the changes, trusting that the experts and taxonomists specialized in the respective genera had arrived at their decisions after having conducted exhaustive studies based on specimens deposited in the world’s major herbaria.

Most of these changes occurred because the respective species were discovered as having been previously described under different names by other botanical authors. These older names, according to international standards of botanical nomenclature, have priority. Other changes resulted when original descriptions were later found to have been poorly interpreted, thus leading to confusions in subsequent classifications, as in the case of Centrosema pubescens, a species described by Bentham in 1837.

Only in February 1987, during a workshop on Centrosema held at CIAT, Cali, Colombia, was the observation made that the type material for C. pubescens did not agree with the species agronomically known by this name and represented, for example, by the commercial varieties Common Centro (Australian) and Centrosema Comum (Brazilian) (Williams and Clements 1990). Instead, the type material agreed with what is considered to be C. schiedeanum, a species that had not yet been validly published—it had previously been known as Clitoria schiedeana Schlecht.—and is represented by the Australian commercial cultivar Belalto.  However, no nomenclature change was proposed at the workshop. Instead, Williams and Clements (1990) suggested continuing with the status quo until a more in-depth taxonomic study should establish the correct name for C. pubescens.

Meanwhile, Fantz (1996) postulated that the correct name for the species agronomically known as C. pubescens was Centrosema molle Mart. ex Benth.  Bentham had also described this species in 1837. However, 22 years later (1859), in his contribution to Martius’ Flora Brasiliensis, he no longer regarded it as a separate species but as a synonym of C. pubescens. Fantz (1996), in a study of Central American material of Centrosema, conducted a detailed analysis of the C. pubescens type, and exhaustively examined all taxonomic treatments involving C. pubescens. He showed that, in the past, the names C. pubescens and C. schiedeanum had indeed been confused, that there were two distinctly different species, and that the name C. pubescens should be replaced by the older, and thus of higher priority, name C. molle, which had previously been regarded as synonym.

Consequently, all material of the species agronomically hitherto known as C. pubescens (except cv. Belalto) should be called Centrosema molle Mart. ex Benth., and all material of the species agronomically hitherto known as C. schiedeanum should be called Centrosema pubescens Benth. The change would apply, for example, to all 1208 accessions of C. pubescens and 49 accessions of C. schiedeanum registered in the World Catalog of Centrosema Germplasm (Schultze-Kraft et al. 1989).

For the non-specialist in taxonomy, the principal difference between the two species is the marked pubescence of, for example, the growing points and inflorescences of C. pubescens (the reason why Bentham chose this name for the species!).   Both species are part of the C. macrocarpum group, which includes not only C. molle and C. pubescens but also C. acutifolium, C. capitatum, C. grandiflorum, C. grazielae, C. macrocarpum, and Centrosema new sp. No. 4 (ined.) (Williams and Clements 1990).

This current suggestion to change names is not merely to fulfill the formality of correct taxonomy per se, but also to comply with the raison d’être of taxonomy: to provide a common denominator for referring to species and thus prevent misunderstandings. This role is particularly important when it concerns species that have given rise to commercial varieties such as cv. Belalto for C. pubescens in Australia and, for C. molle, cvs Common Centro and Cardillo in Australia, Centrosema Comum in Brazil, El Porvenir in Honduras, Villanueva in Cuba, and Barinas (= CIAT 15160) in Southeast Asia. Clear communication is even more important when we consider that germplasm of both species continues to be the subject of agronomic research with the consequent, accompanying  exchanges of information.

Bibliography

Bentham G. 1837. Centrosema DC. Commentationes de leguminosarum generibus. JP Sollinger, Vienna. p 53-56.

Bentham G. 1859. Centrosema. In: Martius CFP de, ed. Flora brasiliensis, 15 vols. CFP de Martius, Munich. Vol 15, part 1, p 124-134.

Fantz PR. 1996. Taxonomic notes on the Centrosema pubescens Bentham complex in Central America (Leguminosae: Phaseoleae: Clitoriinae). Sida (Contrib Bot) 17(2):321-332.

Schultze-Kraft R; Williams RJ; Coradin L; Lazier JR; Kretschmer, Jr, AE. 1989. World catalog of Centrosema germplasm. Centro Internacional de Agricultura Tropical (CIAT); International Board for Plant Genetic Resources (IBPGR), Cali, Colombia.

Williams RJ; Clements RJ. 1990. Taxonomy of Centrosema. In: Schultze-Kraft R; Clements RJ, eds. Centrosema: biology, agronomy, and utilization. Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia. p 1-27.