Ultrastructural Analysis of Pseudanthus (Picrodendraceae) Pollen Using Transmission Electron Microscopy: Intraspecific, Interspecific, Intrafamilial, and Interfamilial Comparisons

Until now investigations on the ultrastructural characteristics of Pseudanthus pollen using transmission electron microscopy (TEM) were limited. The aims of this study were as follows: (1) to present the first comprehensive TEM-based analysis of Pseudanthus pollen; (2) to provide a holistic morphological and ultrastructural description of Pseudanthus pollen; (3) to compare Pseudanthus pollen to that from other Picrodendraceae and closely related families; (4) to clarify intraspecific, interspecific, intrafamilial, and interfamilial character traits of Pseudanthus pollen in relation to that from related genera/families; and (5) to conclude if Pseudanthus pollen could potentially be identified in the palynological record. Pseudanthus pollen samples were collected from anthetic flowers and prepared according to standard methods for investigation with TEM. Interpretations of pollen ultrastructure in other Picrodendraceae and closely related families were based on previously published TEM micrographs. The pollen ultrastructure from six out of nine Pseudanthus species is described here for the first time. By integrating LM, SEM, and TEM techniques, this study offers a holistic perspective on the genus’s pollen morphology and ultrastructural range. It also illuminates the intraspecific and interspecific pollen morphological and ultrastructural diversity within Pseudanthus and how it differentiates from other Picrodendraceae as well as the Euphorbiaceae and Phyllanthaceae. The combined morphological and ultrastructural traits of Pseudanthus pollen render it unique among Picrodendraceae and differentiate it from the pollen of closely related families. This opens the door for future paleopalynological investigations, but until now Pseudanthus pollen has not been reported from the fossil record.