Premise of research. Accumulating data from phylogenetic analyses of living taxa and from paleobotany (pollen, leaves, and floral structures) has greatly improved our understanding of the Cretaceous rise to dominance of the angiosperms. Relatives of the near-basal family Chloranthaceae were conspicuous in the Early Cretaceous. These include female flowers and adhering pollen (Asteropollis) that resemble those of the genus Hedyosmum, but male structures with in situ pollen are not well known. Here we focus on the morphology and ultrastructure of pollen from a spike of unistaminate, ebracteate flowers from the Aptian–Albian Catefica locality and its evolutionary implications.

Methodology. The coalified mesofossil was isolated from unconsolidated sediment by sieving and was cleaned with HCl, HF, and water. In situ pollen was studied using LM, SEM, and TEM. The phylogenetic relationships of the fossil were evaluated with parsimony analysis of a morphological data set with arrangements of living taxa based on molecular studies.

Pivotal results. The pollen aperture is often poorly defined but is most commonly a three-armed sulcus. The exine is reticulate-columellate with a nanoverrucate supratectal sculpture. The nonapertural nexine consists of a thicker foot layer and a thin but continuous endexine that thickens and becomes lamellated under the aperture; the total nexine thickness is less than in most extant Chloranthaceae. Despite some uncertainty due to the thin nexine and similarities between the staminate structure and that of Ceratophyllum, phylogenetic analyses are most consistent with a position attached to the stem lineage of Hedyosmum.

Conclusions. The variable but mainly three-armed sulcus of the Catefica fossil may represent an intermediate stage in the transformation from the ancestral simple sulcus of Chloranthaceae to the four- to six-armed sulcus of typical Asteropollis pollen and living Hedyosmum. Dispersed trichotomosulcate pollen with a chloranthaceous exine structure may be indicative of relatives of Hedyosmum, not only Ascarina, as is sometimes assumed.