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• Acceptances

Monday 29 September to Friday 3 October 2003

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Professor Peter F Stevens

Higher-level names: What is it about them that make us fight so much?

Great advances in our understanding of phylogenetic relationships have been made over the last decade and a half. Major clades in many groups, including flowering plants, now show substantial stability both in terms of content and relationships. This makes possible the development of a system in which only monophyletic (= holophyletic) entitities are named. However, some who want such a system argue that use of the conventional (= Linnaean) system is inappropriate because Linnaeus's understanding of nature has necessarily made "his" naming system impossible in any properly evolutionary context.

Some who challenge the wisdom of naming only such monophyletic groups also argue that their position follows from Darwin's intentions, others, that ancestors cannot be incorporated into a Linnaean classification and that ancestors are an integral part of monophyletic groups, while others more generally invoke the need of users for stable names.

Such issues aside, the current nomenclatural system has problems if our goal is indeed to name only monophyletic groups. I argue that most of the apparently more cosmic issues brought up in this naming debate are based on a combination of a misunderstanding of the nature and purpose of language, fallacious reasoning, and a dubious interpretation of history. Thinking of naming systems as some kind of convention may help clarify what we should be doing, if we are not to squander both the time and the reputation of systematics.

Already time is in short supply and our reputation not what it might be; solving the less cosmic issues may involve a self-discipline that also seems in short supply in the systematic community.

Peter Stevens is Professor of Biology at the University of Missouri, St Louis, and Curator at the Missouri Botanical Garden. His research covers several different areas, including investigation of morphological and molecular characters and character states. His work on the history of systematics focuses on how the protean connotations of botany and natural history have affected the development of the scientific disciplines that draw on those disciplines. His taxonomic work is focused on several groups, mostly centered in Malesia or with strong Malesian representation, in particular, Clusiaceae and Ericaceae

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Pauline Ladiges FAA

Australian biogeographic connections and the phylogeny of myrtaceous groups

The phylogeny of the eucalypt and melaleuca groups of Myrtaceae is compared with geological events and ages of fossils to discover the time frame of clade divergences.

The Australasian eucalypt group includes seven genera, of which some are relictual rainforest taxa of restricted distribution and others are species-rich and widespread in drier environments. Based on molecular and morphological data, phylogenetic analyses have identified two major clades. The monotypic Arillastrum endemic to New Caledonia is related in one clade to the more species-rich Angophora, Corymbia and Eucalyptus that dominate the sclerophyll vegetation of Australia. Based on the time of rifting of New Caledonia from eastern Gondwana and the age of fossil eucalypt pollen, it is argued that this clade extends back to the Late Cretaceous. The second clade includes three relictual rainforest taxa, with Allosyncarpia from Arnhem Land the sister taxon to Eucalyptopsis of New Guinea and the eastern Indonesian archipelago, and Stockwellia from the Atherton Tableland in north-east Queensland. As monsoonal, drier conditions evolved in northern Australia, Arnhem Land was isolated from the wet tropics to the east and north during the Oligocene, segregating ancestral rainforest biota.

The distribution of species in Eucalyptopsis and Eucalyptus subgenus Symphyomyrtus endemic in areas north of the stable edge of the Australian continent, as far as Sulawesi and the southern Philippines, may also relate to the geological history of South East Asia-Australasia. Colonisation (dispersal) may have been aided by rafting on micro-continental fragments, by accretion of arc terranes onto New Guinea and by land brought into closer proximity during periods of low sea-level, from the Late Miocene and Pliocene. The phylogenetic position of the few northern, non-Australian species of Eucalyptus subgenus Symphyomyrtus suggests rapid radiation in the large Australian sister group (s) during this time-frame.

A similar pattern, connecting Australia and New Caledonia, is emerging from phylogenetic analysis of the Melaleuca group within Myrtaceae, with Melaleuca being polyphyletic.

Pauline Ladiges is Head of the School of Botany at The University of Melbourne and a Fellow of the Australian Academy of Science. Her research interests are phylogenetic systematics and historical biogeography of Australian plants, and she is best known for her work on the eucalypts. With Gareth Nelson she has developed the biogeographic method of sub-tree analysis.

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Professor Robert S. Hill

Fire, Air, Water and Earth: an elemental prehistory of Australia

Extinction, evolution, and major changes in distribution characterise Australian vegetation history and it is clear that the current vegetation is just one stage in a long, ongoing, and largely unpredictable series of events. The living Australian vegetation is the product of many millions of years of evolution on a very old and mostly stable land mass. The flat and highly eroded landscape provides an often nutrient-depleted substrate for the vegetation, the generally low and erratic rainfall adds further pressure to this, and the dry conditions that follow provide excellent fuel should a fire ignition source occur.

The plant fossil record in southern Australia is now well enough understood to provide significant data towards the reconstruction of the past responses to these conditions as they changed through time.

Many elements of the vegetation are ancient, and have changed little through many millions of years.

Bob Hill is an ARC Professorial Research Fellow at the University of Adelaide and Head of Science at the South Australian Museum. He has recently accepted the position of Head of the newly formed School of Earth and Environmental Sciences at the University of Adelaide. His research centers around the evolution of the Australian vegetation and the response of plants to long term climate change.

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Professor Brent D. Mishler

Phylogeny of the land plants, with special reference to bryophytes

The reconstruction of phylogenetic relationships of green plants is important both for practical concerns and for understanding of major evolutionary events such as the origin of multicellularity, diversification of life-history strategies, and the conquest of land. Phylogenetic understanding of green plants has rapidly increased over the last decade due to new methods of data gathering and data analysis, as well as an increased coordination of effort among different laboratories (see the "Deep Green" web page at: http://ucjeps.berkeley.edu/bryolab/greenplantpage.html).

I will focus here on the cladistic relationships of the tracheophytes (vascular plants) to the "green algae" and "bryophytes" (and the relationships within the major bryophyte groups). The green algae are composed of several major lineages, one of which (the "charophytes") contains the land plants (i.e., bryophytes plus tracheophytes). In turn, the bryophytes are composed of three or four major lineages (i.e., liverworts, hornworts, mosses, and perhaps Takakia); these lineages are paraphyletic with respect to the tracheophytes. However, their precise branching order has remained problematic. Many data sets (but by no means all) show the liverworts alone to be the basal lineage within extant land plants and the mosses as the sister group of tracheophytes (the relationships of Takakia and the hornworts being less clear). Analyses at a level so deep (with relatively short internodes of interest mixed with long terminal branches) are quite difficult, and pose new challenges to theory and algorithms. Coordinated, combined analyses of molecular and morphological data offer the greatest future potential for progress.

A newly funded NSF Tree of Life grant is addressing these issues by completing a matrix of comparable morphological and ultrastructural data, plus whole genome sequences for chloroplasts and mitochondria, for more than 50 representatives of the critical deep-branching lineages of green plants. A backbone phylogeny will be developed with this global data set and then connected with local phylogenies (that have many more OTUs, but fewer and different characters), using a variety of compartmentalization and supertree approaches. Preliminary analyses illustrating these approaches will be presented.

Brent Mishler is Director of the University and Jepson Herbaria at University of California, Berkeley, as well as a professor in the Department of Integrative Biology, where he teaches systematics and plant diversity. A native southern Californian, he received his Ph.D. from Harvard University in 1984, then was on the faculty at Duke University for nine years before moving to UC Berkeley in 1993. His research interests are in the systematics, evolution, and ecology of bryophytes, especially the diverse moss genus Tortula, as well as in the phylogeny of green plants and the theory of systematics.

 

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