Sister group relationships of the large, important flowering plant families Fabaeae and Rosaceae are uncertain. Recent studies (e.g. Angiosperm Phylogeny Group, Ann. Missouri Bot. Gard. 85:531-553; Soltis et al., 1999, Nature 402:402-404) find strong support for including Fabales and Rosales within the Eurosid I group, which also includes Cucurbitales and Fagales. Fabales consists of four families, with the Polygalaceae, Surianaceae, Quillajaceae each suggested as the sister group to the Fabaceae. Rosaceae are currently seen as the sister group to the remainder of the Rosales. Nucleotide sequence data from the chloroplast matKgene are used for phylogenetic analyses of representatives of most families of Eurosid I with the primary aim of resolving the sister group relationships of Fabaceae and Rosaceae. Preliminary results indicate strong support for Eurosid I and less support for relationships among its four orders. matKsequence data do, however, appear to provide sufficient characters to help resolve relationships within Rosales and Fabales.

Key words: eurosids I, Fabaceae, phylogeny, Rosaceae