Search

The first comprehensive phylogenetic study of the Australasian shrubby everlastings Ozothamnus, Cassinia, and their satellite genera is presented based on the nuclear ribosomal external and internal transcribed spacer and three chloroplast spacer regions ( mat K- psb A, psb A- trn H, ycf6- pbs M). While the hypothesis of the monophyly of the sequence copies found in Cassinia cannot be rejected, sequences from Ozothamnus are found to be non-monophyletic in three possible taxonomic circumscriptions of that genus. Cassinia, Calomeria, Odixia and Haeckeria are nested in a narrowly circumscribed Ozothamnus. Ozothamnus section Hebelaena, a sub-shrubby group long recognized as potentially misplaced in the genus, is more heterogeneous than expected and is found to be potentially polyphyletic. Perhaps more surprisingly, a group of four species previously considered part of 'core' Ozothamnus is found to be more closely related to other genera. It includes the subalpine 'cascade everlastings' of south-eastern Australia. Although many characters traditionally used for the delimitation of genera are homoplasious, connivent involucral bracts and presence of paleae are synapomorphies for Cassinia. Except for the robust shrubby habit, no morphological synapomorphy for core Ozothamnus/ Cassinia is currently evident. Future studies are needed to test these results with additional data, to identify morphological and anatomical synapomorphies for individual clades and to resolve species-level relationships with more extensive sampling to address the possibilities of incomplete lineage sorting or reticulate evolution. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article about phylogenetic classification of evolutionary divergence.