Fallacies and false premises—a critical assessment of the arguments for the recognition of paraphyletic taxa in botany

Abstract

One of the central controversies in contemporary taxonomy and systematics revolves around whether to accept or to reject paraphyletic taxa. The present review is the result of a survey of the ongoing discussion in botany over the past ca. 15 years, and attempts to systematically and critically assess all individual arguments presented for the formal recognition of paraphyletic groups in the classification of life. Where arguments are found to be without merit, rebuttals are presented in the hope of excluding them from further discussion, which can then concentrate on those that have merit. Where arguments are found to be sound, their implications and possible solutions are discussed. The controversy around paraphyletic taxa can be broken down into three questions: whether their rejection or acceptance would lead to a classification better reflecting patterns of biological diversity and evolutionary history; whether their rejection or acceptance would lead to a more practical, useful and predictive classification; and whether their rejection is compatible with ranked and binary Linnaean taxonomy. All available arguments for paraphyletic taxa relating to the first question are demonstrated to be based on various logical fallacies or false premises, especially misunderstandings of the principles of phylogenetic systematics. The issue of usefulness is harder to resolve, as different classifications serve different needs. It is presumably unavoidable but also preferable that phylogenetic and non‐phylogenetic ways of classifying species continue to coexist, serving different needs. Finally, an insistence on monophyletic taxa is found to be incompatible with binary taxonomy under a set of very specific circumstances and assumptions whose presence and accuracy are not universally accepted. © The Willi Hennig Society 2011.

Total evidence phylogeny of Pontederiaceae (Commelinales) sheds light on the necessity of its recircumscription and synopsis of Pontederia L.

“…Nonetheless, until very recently (Pellegrini 2017a), the taxonomy of the family remained dogmatic and outdated, with the recognition of several non-monophyletic taxa. The arguments used as the basis for maintaining such assemblages are based especially on misunderstandings of the principles of phylogenetic systematics (Schmidt-Lebuhn 2012). According to Simpson (2006), one of the main paradigms of modern phylogenetic systematics is the proposal of classification systems that accurately reflect the evolutionary history of the studied group, being simultaneously easy to use.…”

A community‐derived classification for extant lycophytes and ferns

“…The stability of names is thus of great importance, and it is critical to consider existing classifications when determining taxa worthy of recognition and the ranks at which to treat them. A focus on natural groups is similarly important, as it results in classifications that reflect evolutionary history (Schmidt‐Lebuhn, ) and ultimately lead to greater stability. Although we acknowledge the validity of some arguments presented in favor of maintaining paraphyletic taxa (see, e.g., Hörandl & Stuessy, ), we ultimately reject this practice and aim to recognize only monophyletic lineages at the genus level and above.…”

Monophyly or Paraphyly– The Taxonomy of Holcoglossum (Aeridinae: Orchidaceae)

“…Evolutionary classification recognizing paraphyletic groups argues the following: (1) there are two criteria for biological classification, i.e., similarity and common descent [12]; (2) many species are paraphyletic [1], [12]–[14]; (3) paraphyletic groups are natural transitional stages in the evolution of taxa and are natural units of biological classification [4]; (4) cladistic classification is incompatible with the Linnean hierarchy system [1], [4], [7], such as diachronous groups and (5) classification based only on common descent often fails to reflect divergence and natural selection. In contrast, cladistic classification states the following: (1) only monophyletic groups in their strictest sense (holophyly) that are evidenced by synapomorphous characters are recognized in biological classification; (2) only species and clades are objective, and supraspecific taxa are terminals in cladistic classification [15], [16]; (3) there are no objective criteria to circumscribe paraphyletic groups, and paraphyletic groups are artificial classes created by taxonomists to emphasize some particular characters or divergence [5], [16]–[18] and (4) cladistic classification can be accommodated within the Linnaean system except for monotypic higher taxa and historic groups [19], with the former being neither paraphyletic nor monophyletic and the latter being dismissed [16], [19]. However, as there are many theorical and lengthy discussions anywhere [1]–[11], a discussion of the merits and fallacies of each school of classification is not the major aim of present paper.…”