Phylogenetic relationships in tribe Spiraeeae (Rosaceae) inferred from nucleotide sequence data

Tribe Spiraeeae has generally been defined to include Aruncus, Kelseya, Luetkea, Pentactina, Petrophyton, Sibiraea, and Spiraea. Recent phylogenetic analyses have supported inclusion of Holodiscus in this group. Spiraea, with 50-80 species distributed throughout the north temperate regions of the world, is by far the largest and most widespread genus in the tribe; the remaining genera have one to several species each. Phylogenetic analyses of nuclear ITS and chloroplast trnL-trnF nucleotide sequences for 33 species representing seven of the aforementioned genera plus Xerospiraea divided the tribe into two well supported clades, one including Aruncus, Luetkea, Holodiscus, and Xerospiraea, the second including the other genera. Within Spiraea, none of the three sections recognized by Rehder based on inflorescence morphology is supported as monophyletic. Our analyses suggest a western North American origin for the tribe, with several biogeographic events involving vicariance or dispersal between the Old and New Worlds having occurred within this group.