Morphology, Ultrastructure and Evolutionary Significance of Pollen in a Chloranthaceous Staminate Structure from the Early Cretaceous of Portugal

Premise of research. Accumulating data from phylogenetic analyses living taxa and paleobotany (pollen, leaves, floral structures) has greatly improved our understanding the Cretaceous rise to dominance angiosperms. Relatives near-basal family Chloranthaceae were conspicuous in Early Cretaceous. These include female flowers adhering pollen (Asteropollis) that resemble those genus Hedyosmum, but male structures with situ are not well known. Here we focus on morphology ultrastructure a spike unistaminate, ebracteate Aptian–Albian Catefica locality its evolutionary implications.Methodology. The coalified mesofossil was isolated unconsolidated sediment by sieving cleaned HCl, HF, water. In studied using LM, SEM, TEM. relationships fossil evaluated parsimony analysis morphological set arrangements based molecular studies.Pivotal results. aperture is often poorly defined most commonly three-armed sulcus. exine reticulate-columellate nanoverrucate supratectal sculpture. nonapertural nexine consists thicker foot layer thin continuous endexine thickens becomes lamellated under aperture; total thickness less than extant Chloranthaceae. Despite some uncertainty due similarities between staminate structure Ceratophyllum, consistent position attached stem lineage Hedyosmum.Conclusions. variable mainly sulcus may represent an intermediate stage transformation ancestral simple four- six-armed typical Asteropollis Hedyosmum. Dispersed trichotomosulcate chloranthaceous be indicative relatives only Ascarina, as sometimes assumed.