Lennoaceae are a small family of root parasites endemic to Mexico and the southwestern United States. These plants are non-photosynthetic and exhibit a reduction of morphological features which makes systematic placement difficult. Earlier studies of Lennoaceae based on floral and pollen morphology have suggested relationships with Boraginaceae, "Hydrophyllaceae," or Verbenaceae. Molecular evidence is presented from all three genomic compartments to test these hypotheses. The plastid gene rps2, the mitochondrial genes cox1 and atpA and the nuclear ITS region were sequenced and subjected to phylogenetic analysis. Preliminary results indicate that a monophyletic Lennoaceae is most closely related to Ehretioideae, a subfamily of Boraginaceae. This subfamily contains host plants of Lennoaceae, indicating a possible case of adelphoparasitism, the first such association suspected among the angiosperms. Further investigation should resolve this question and determine the closest extant relative of Lennoaceae among this group.

Key words: adelphoparasitism, Boraginaceae, Hydrophyllaceae, Lennoaceae, mitochondrial DNA, parasitic plant