NUCLEOTIDE-SEQUENCES OF THE RBCL GENE INDICATE MONOPHYLY OF MUSTARD OIL PLANTS

Nucleotide sequences for the chloroplast rbcL gene were obtained from representatives of 11 of the 15 plant families known to produce glucosinolates (mustard oil glucosides). Parsimony analyses indicate that these constitute two widely separated groups and thus imply two independent origins of the mustard oil/myrosin cell syndrome. A strongly supported, major group comprises the mustard family Brassicaceae and its near relatives Capparaceae, Resedaceae, and Tovariaceae along with such morphologically diverse taxa as Bataceae, Bretschneideraceae, Caricaceae, Limnanthaceae, Moringaceae, and Tropaeolaceae. The second mustard oil group is restricted to the euphorbiaceous genus Drypetes. Akania, the subject of an independent rbcL analysis, pairs with Bretschneidera, and these are collateral with Tropaeolum at the base of the major mustard oil clade. Gyrostemonaceae, Pentadiplandra, and Salvadoraceae have not been analyzed for rbcL sequences. The gene data corroborate many aspects of Rodman's recent cladistic analysis based predominantly on morphological characters; together the molecular and morphological evidence support Dahlgren's radical classification of an expanded order Capparales.