1. Netherlands Centre for Biodiversity Naturalis (Section NHN), Leiden University, PO Box 9514, NL‐2300 RA Leiden, The Netherlands
2. (Authors for correspondence: Frederic Lens tel +31 71 527 3570;Siegbert Melzer tel +49 431 880 3345;)
3. Laboratory of Plant Systematics, Institute of Botany and Microbiology, Kasteelpark Arenberg 31 Box 2437, K.U. Leuven, BE‐3001 Leuven, Belgium
4. Present address: Plant Breeding Institute, Christian‐Albrechts‐University Kiel, Am Botanischen Garten 1‐9, D‐24118 Kiel, Germany