XVI International Botanical Congess

Dirca is an enigmatic genus comprised of three species: D. palustris with a broad geographic distribution in eastern U.S. and Canada, D. occidentalis with a restricted distribution in California, and D. mexicana with an ultra-restricted distribution in the state of Tamaulipas, Mexico. An effort will be made to identify some factors leading to the species distribution patterns. In addition, an attempt will be made to show the relationships among the three species and to identify relationships with other genera within the family.