HEDYOSMUM-LIKE FOSSILS IN THE EARLY CRETACEOUS DIVERSIFICATION OF ANGIOSPERMS

摘要

Premise of research. Early Cretaceous Hedyosmum-like fossils are important because they provide information on the pistillate flowers and fruits of plants that produced Asteropollis pollen, which is common and widely distributed very early in the history of angiosperms. Hedyosmum (Chloranthaceae) is also the only extant genus for which there is a plausible fossil presence at such an early stage of angiosperm evolution. Methodology. The fossils were sieved out of unconsolidated sediments and cleaned with HF, HC1, and water. External morphology and internal anatomy were studied using scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy. Pivotal results. New information on Hedyosmum-)ke fossils is provided based on pistillate flowers and fruits with adhering Asteropollis pollen from the Early Cretaceous of Portugal. The fossils are assigned to a new Early Cretaceous taxon, Hedyflora crystallifera, which in external morphology is closely similar to extant Hedyosmum. However, the fossils differ from the extant genus in having a crystalliferous endotesta with cells that have endoreticulate infillings, a feature characteristic of all extant Chloranthaceae except Hedyosmum. Extant Hedyosmum has a thin, unspecialized seed coat. This new discovery confirms earlier predictions that an endotestal seed coat is ancestral for Chloranthaceae as a whole but has been lost in the lineage leading to extant Hedyosmum. Conclusions. Hedyflora confirms the divergence of the Hedyosmum lineage from other Chloranthaceae very early in the angiosperm radiation but refutes these early fossils as evidence of extant Hedyosmum in the Early Cretaceous.