Pollen diversity of Xenostegia D.F.Austin et Staples (Convolvulaceae)

Abstract

Xenostegia D.F.Austin et Staples is a small genus in the family Convolvulaceae, with five species restricted to Africa, and one species widespread across the Paleotropics. It was initially established to accommodate two species in Merremia that possessed non-spinulose pantoporate pollen, rare in the family, along with stigma and anther characters that did not fit other genera entirely. Recent molecular studies, and the discovery of a new species in Central Africa, have expanded the delimitation of this genus from two to six species. Our survey captures the palynological variation of all currently documented species of Xenostegia, revealing that more types of pollen aperture patterns are present (15- and 30-colpate), with implications for the circumscription of the genus. In addition, a unique pattern of exine sculpture (plurigemmate-echinate) was discovered, which is shared by all the species and has not yet been documented in any other member of family Convolvulaceae.

Keywords:

• Africa
• Merremia
• exine ornamentation
• taxonomy

Acknowledgements

The authors would like to thank the assistance of Dr Carol Furness and Dr Hannah Banks (Jodrell Laboratory, Royal Botanic Gardens, Kew, UK), and Mrs Iris Van der Beeten (Meise Botanic Garden, Belgium) in the development of the palynological analysis; Dr Olivier Leroux (Systematics and Evolutionary Botany Lab, Department of Biology, University of Ghent, Belgium) for support in the preparation of the image plates; also, André Luiz da Costa Moreira and Daiane Alves dos Santos (Universidade Estadual de Feira de Santana, Brazil) for insightful discussions on pollen variation in Convolvulaceae; and Dr Marc Sosef (Meise Botanic Garden, Belgium) and Dr Lars Chatrou (Systematics and Evolutionary Botany Lab, Department of Biology, University of Ghent, Belgium) for useful comments on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Fundação para a Ciência e Tecnologia, PhD Grant [SFRH/BD/45924/2008] (2009–2013) which allowed conducting the palynological work at the Jodrell Laboratory, Kew, UK; and Synthesys [Grant BE-TAF-2468], which allowed the examination of herbarium collections of Xenostegia at BR herbarium (2019).