Systematics of the angiosperm family Haloragaceae R. Br. emphasizing the aquatic genus Myriophyllum: Phylogeny, hybridization and character evolution

Date of Completion

January 2004


Biology, Botany




Haloragaceae are a relatively small family of 8 genera and approximately 120 species; yet, they display a rare and extreme diversity in habit, ranging from small trees to submerged aquatics. The center of diversity for the family is Australia where three genera are endemic. Four genera are primarily terrestrial (Glischrocaryon, Gonocarpus, Haloragis, and Haloragodendron ) while four are aquatic/semi-aquatic (Laurembergia, Meziella, Myriophyllum and Proserpinaca). Myriophyllum is the most speciose Haloragaceae genus (≈60 spp.) and has a cosmopolitan distribution. Evolutionary relationships within Haloragaceae have been difficult to ascertain, particularly due to uncertain placement of the various aquatic/semi-aquatic genera in relation to each other and the terrestrial taxa. Phylogenetic analyses using both chloroplast (trnK, matK) and nuclear (ITS-1, ITS-2 and 5.8S) DNA sequence data have given insight into relationships among all the genera and many species of Haloragaceae. The terrestrial woody genera (Glischrocaryon and Haloragodendron) are basal-branching in the family, and form a clade sister to the rest of the family. The position of the recently rediscovered monotypic genus Meziella is supported as monophyletic with Myriophyllum. The semi-aquatic species Haloragis brownii and H. tenuifolia are only distantly related to other Haloragis and have unique morphological characters that argue for their distinct generic status. Phylogenetic analyses support some of the generic and subgeneric limits in Haloragaceae as proposed in Orchard's (1975) treatments, but some striking differences are apparent involving the generic limits of Glischrocaryon, Gonocarpus and Haloragis. The large aquatic genus Myriophyllum is divided into two distinct clades and several new taxa have been uncovered through phylogenetic analyses. The aquatic genera do not form a clade and the aquatic habit may have evolved independently multiple times in Haloragaceae. Alternatively a reversal from the aquatic habit to terrestrial habit may have evolved. ^