The Chenopodiaceae and Amaranthaceae are closely related families consisting of about 174 genera and 2,050 species of world-wide distribution. The Chen-Am alliance is ecologically important and also contains a number of economically important crop and weedy species. The alliance is further noted for C4 photosynthesis as well for adaptations to xeric and saline environments. The Chen-Ams traditionally have been considered allied based on a shared core floral formula, as well as morphological, anatomical, chemical, and molecular data. Despite their importance, the phylogeny of the Chen-Ams has not been investigated. We report here a preliminary analysis of the phylogeny of the Chen-Am alliance based on plastid ndhF gene sequences. All currently recognized subfamilies and tribes (except the Polycnemoideae) were sampled including over 15 genera. Parsimony analysis of ndhF strongly supports a monophyletic Chen-Am alliance. Based on sampling to date, the Chenopodiaceae as currently circumscribed is paraphyletic, and the Amaranthaceae is potentially polyphyletic.

Key words: Amaranthaceae, Chenopodiaceae