Comparative palynology and seed morphology in annual pansies (Viola sect. Melanium, Violaceae): implications for species delimitation

Abstract

This integrated study provides new insights into pollen and seed morphology and pollen heteromorphism of four closely related annual taxa of Viola sect. Melanium. The plant material, both fresh and dried, was collected in Italy and studied using light and scanning electron microscope. Palynological data for V. hymettia together with a detailed comparative analysis of seed morphology and micromorphology of the four species are reported for the first time. Results of this work highlight some pollen and seed features as useful diagnostic characters. The pollen size proves to be of diagnostic value to easily separate V. kitaibeliana, having the smallest pollen grains, from the others, especially from V. arvensis with the largest ones. Exine ornamentation is microreticulate, showing no relevant differences among species. We can partially confirm the diagnostic value of the prevailing pollen morph as it can be useful only for V. arvensis (five-aperturate) versus V. tricolor and V. hymettia (four-aperturate). The macro- and micromorphology of seeds provide additional useful distinguishing characters. Particularly, seed size was found to be a good delimitating character, especially to distinguish V. kitaibeliana (with the smallest seeds) from V. arvensis, and easy to be measured with no need of particular equipment.

Keywords:

• Diagnostic characteristics
• Europe
• pollination ecology
• pollen morphology
• reproductive biology
• scanning electron microscopy
• seed coat
• seed dispersal

Acknowledgements

We are grateful to A. Gennaro and S. Bitti of the Laboratory of Plant Cytogenetics (Tuscia University, Viterbo) for cytological analyses. We also thank S. Buono, S. Ballelli, F. Bartolucci, M. Bovio, F. Conti, E. Lattanzi, and F. Prosser for materials and useful information. The authors gratefully acknowledge MIUR (Ministry for Education, University and Research) for financial support (Law 232/216, Department of excellence). The authors are grateful to T. Marcussen and the reviewers for their valuable and constructive comments which have helped in improving the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The study visits in the Herbaria of Copenhagen (C), Budapest (BP), Madrid (MA), and Wien (W) received support from the SYNTHESYS Projects DK-TAF-4177, HU-TAF-4506, ES-TAF-7076, and AT-TAF-7074 (www.synthesys.info) which were financed by European Community Research Infrastructure Action under the FP7 “Capacities” Programme.