Compositae metatrees: The next generation

VICKI A. FUNK, ARNE A. ANDERBERG, RANDALL J. BAYER, S. E. FREIRE, ET AL.

Systematics and Evolution of the Compositae (Book TICA)

International Association for Plant Taxonomy (IAPT) Vienna

Año: 2009; p. 747 - 770

The Calyceraceae-Compositae clade (as we know it today) may have originated in southern South America ca. 50?41 Ma, and the diversifi cation of the family started in the same area. The diversifi cation of Calyceraceae was modest by comparison with that of Compositae, which have traveled the globe. In Compositae, following the southern South American radiation, there was an African explosion. Of the 1600?1700 genera in Compositae today,about two-thirds are in clades with the basal branches in Africa, many in southern Africa.In fact, with the exception of the Mutisieae (sensu Cabrera) grade at the base and the highly nested Heliantheae Alliance, all of the major clades in the family appear to have an African origin or a major African presence near the base of their phylogenies. From this African origin came numerous movements into Asia, Eurasia, Europe, Australia, etc., many of which have spawned substantial radiations (e.g., Cardueae, Vernonieae, Anthemideae). Bremer (1994) started the process of updating the characters attributed to a hypothetical ancestor and Lundberg has added to the list. Here we have refi ned some of the characters and added a few more. Here we offer a list of potential plesiomorphic characters for the extant members of Compositae: Shrubs or subshrubs, no internal secretory systems; Inflorescence cyme-like; Leaves alternate and spirally inserted;Heads indeterminate, few heads per plant, each with many flowers; Involucral bracts in several series, imbricate without hyaline or scabrous margins; Receptacle naked; Florets perfect and fertile, arranged in a head, parts in 5?s; mostly one type of fl ower, some diff erentiation in floral morphology in peripheral florets possible but without true rays; Corolla white or possibly pink, yellow or blue probably 5-lobed, lobes deeply divided and with much variation; Stamens alternate with the corolla lobes, anthers fully connate at the margins with the filaments free with upper part of filaments forming a filament collar, thecae spurred and possibly tailed (caudate), possibly without apical appendage,dehisce by longitudinal slits, pollen kit present, Pollen grains 3-celled, pollen prolate and psilate; Styles slender, shortly bifid, without hairs; solid band of stigmatic surface on inside of style branches; ovary consistently inferior with ovule in a basal position;Pappus of capillary bristles; Fruit an indehiscent achene ribbed; Base chromosome number: x = 9; Secondary chemistry simple and characterized by a small number of fl avonoids, polyacetylenes, coumarins, and triterpenes; Southern South American in distribution; probably growing in open dry habitats. Advances in genomics are changing the way we do research in systematics. Phylogenomics, the use of whole genomes for phylogenetic studies, is already occurring in many plant and animal groups and at ever increasing speeds and will no doubt become the standard of the future in Compositae systematics as costs decrease and technology becomes more widely available.Whole chloroplast genomes have already been sequenced for many plant groups and used in phylogenetic studies, particularly for establishing the position of basal angiosperms. Phylogenomic studies in Compositae lag considerably behind those of the Angiosperm Phylogeny Group (APG) and that of many animals groups as well. Although the genomes of a number of Cichorioideae taxa are currently under study (Rieseberg, pers. comm.) only two economically important taxa, Helianthus annuus L. and Lactuca sativa L., are the subject of a coordinated, large scale eff ort. The Compositae Genome Project (CGP), headquartered at the UC Davis Genome Center, has a wide range of objectives for its studies of lettuce and sunfl ower (and presumably others in the future). The goal as given on the home page http://compgenomics.ucdavis.edu/index. php) is to ?integrate information at the genetic, physiological and population/evolutionary levels for a broad range of genes involved in evolution of cultivated plants and weeds, evaluate the relative importance of changes in gene sequence versus gene expression in phenotypic evolution, determine the genotypic consequences of parallel phenotypic evolution, and provide a basis for future functional analyses.? For most systematists, however, the focus of whole genome sequencing will be on more accurately reconstructing the evolutionary history of a particular group of plants, most of which are not cultivated and for which the vast funding required to map genes and determine their functions will likely never be available. As in all molecular studies, a cautionary note has been sounded relative to the resolving power of genomics for phylogenetic study. Data analysis of huge numbers of sequences is daunting and will probably still require collaboration with mathematicians and bioinformaticists. Another issue is lack of congruence,particularly with existing trees. Hervé Philippe stresses that datasets will have to be reanalyzed with diff erent methods in order to determine the best tree. The latter is not necessarily guaranteed by more data. Additionally,taxon sampling will remain an issue. Lots of information from only a few taxa does not guarantee a sound phylogeny no matter how cutting-edge the sequencing or the analyses. Still, we can expect that genomes will be increasingly common tools in future phylogenetic studies. Hopefully, as the data accumulate there will be better resolution of taxonomic placements, particularly in the location of Senecioneae and at the base of the Compositae family tree where the position of some mutisioids and some enigmatic genera remain unclear.