A linear polyad: a distinctive pollen dispersal unit in Xyris complanata (Xyridaceae)

Abstract

This is the first study on pollen from Xyris complanata using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Pollen in various conditions, including acetolysed, hydrated, and dehydrated states, were examined. The results show that X. complanata plants disperse their pollen in a linear polyad, comprising a cohesive elongate uniplanar tetragonal tetrad aggregate, consisting of 4 to 10 tetrads per unit. The cohesion within and between tetrads is accomplished by means of the fusion of the tectum. The individual grains are medium in size, pollen grains of intermediary tetrad are quadrangular in both polar and equatorial views, pollen grains of apical tetrad are obovoid in shape, both are triangular in frontal equatorial view, exine 3.0 ± 0.2 μm thick, ulcerate covered with a fossulate–perforate operculum, and heterobrochate microreticulate–perforate sculpturings. Pollen wall consists of the tectum, columellae, footlayer, and endexine, with pollenkitt. The dispersal unit and apertural type are distinctive characters, since, among Xyris, such features can only be found in pollen of X. complanata. The results of the present study contribute useful characters for the systematic study of plants in the genus Xyris.

Keywords:

• dispersal unit
• pollen
• polyads
• tetrad
• Xyris complanata

Acknowledgements

This article is dedicated to Ao. Univ.-Prof. Mag. Dr Reinhard Zetter, the doctoral advisor of the first author, on the occasion of his retirement from the University of Vienna, Vienna, Austria. The authors are also very grateful to the Herbarium of the Department of Biology, Faculty of Science, Prince of Songkla University and the Singapore Botanic Gardens Herbarium, for providing Xyris complanata specimens, and thus making this project possible. The anonymous reviewers, Associate Professor Dr Martina Weber, and Dr Silvia Ulrich are thanked for their helpful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This project was funded by the Prince of Songkla University (contract number SCI600567S) and the Plant genetic conservation project under the Royal Initiative of Her Royal Highness Princess Maha Chakri Sirindhorn (project number SCI600112S).