Origin and Evolution of Endemic Asteraceae From the Macaronesian Archipelagos

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9707614 Jansen In collaboration with foreign colleagues Drs. Javier Francisco-Ortega and Arnoldo Santos-Guerra, Dr. Robert Jansen of the University of Texas is studying the phylogeny and biogeography of several genera of sunflower relatives, family Asteraceae, on the islands of the Macaronesian archipelago, the Canaries, Madeiras, and Azores. Over 800 species of plants have been described that are endemic to these islands (found nowhere else), and 25% of these belong to the family Asteraceae, which shows instances of evolutionary radiation both among islands and elevationally on single islands. New evidence from DNA sequencing of chloroplast and nuclear genes, from samples of island species and from collections provided by colleagues from African and Mediterranean species suspected to be related, will help construct phylogenetic trees or genealogies for such genera as Argyranthemum, Cheirolophus, Pericallis, and Tolpis. Where modern monographic treatments exist of the genera, such as for Argyranthemum, the molecular evidence can be integrated with morphological characters described for all the species, to assess rates and patterns of change among species in select floral and vegetative features. The phylogenetic studies on Cheirolophus (tribe Cardueae), Pericallis (tribe Senecioneae), and Tolpis (tribe Lactuceae) will contribute to nascent efforts to determine the phylogenetic tree structure for these large subgroups of the sunflower family on a world-wide basis. Numerous conflicting or overlapping theories have been proposed to explain the number and distribution of endemic species on the Macaronesian islands, but without a well supported phylogenetic framework to guide hypotheses about evolution and migration, the theorizing may continue unconstrained. Whether the African mainland or Mediterranean regions have served as sources for migrants to Macaronesia, whether back migration may have occurred, whether single or few migrants radiated into numerous new species as opposed to multiple in troductions from continental sources creating the diversity of the islands, whether speciation has occurred more often between islands or between elevation zones on individual mountainous islands_all these questions of biogeography can be studied within a robustly supported phylogenetic framework of the several groups of plants under consideration.