CIRCUMSCRIPTION OF MYRTALES AND THEIR RELATIONSHIPS TO OTHER ROSIDS -EVIDENCE FROM RBCL SEQUENCE DATA

Despite intensive morphological and chemical studies on the Myrtales, the circumscription of the order remains poorly defined. To test the m onophyly of Myrtales sensu Dahlgren and Thorne (Annals of the Missouri Botanical Garden 71: 633-694, 1984), determine the relationships of s ome controversial families, and identify the most likely sister group of Myrtales, we conducted parsimony analyses on 80 rbcL sequences repr esenting 36 taxa from families traditionally included in Myrtales and 44 taxa from other Rosidae. The consensus tree resulting from these an alyses supports the monophyly of Myrtales and is substantially congrue nt with the circumscription of the order proposed by Dahlgren and Thor ne (Annals of the Missouri Botanical Garden 71: 633-694, 1984), with o ne notable exception: in the rbcL tree Vochysiaceae are placed in Myrt ales. A reanalysis of morphological attributes of Vochysiaceae reveale d that the inclusion of the family in Myrtales is also supported by th e combined occurrence of two typical myrtalean features of the wood: v estured pits and bicollateral vascular bundles. Furthermore, our analy ses excluded Thymelaeaceae, Lecythidaceae, Haloragaceae, and Gunnerace ae from Myrtales, suggesting that the association of these families wi th Myrtales, as previously proposed by other authors, may not reflect common ancestry. Finally, our analyses support a sister group relation ship between the order Myrtales and a clade formed by an expanded Malv ales, Sapindales, and an expanded Capparales.