Trimerous magnoliid flowers with a unique set of floral and pollen traits from the Late Cretaceous of Southern Bohemia (Czech Republic).

Floral structure is a key aspect of angiosperm diversity. Recent research revealed that significant floral disparity was already present in the Cretaceous. However, our understanding of early floral diversity remains limited, as it is directly dependent on the fossil record. We describe a new, exceptionally well-preserved flower with in situ pollen from the Klikov Formation (late Turonian - Santonian). Our phylogenetic analyses support relationships with the magnoliid order Piperales. Based on a morphospace analysis, we show that the new fossil is among the most morphologically divergent angiosperm flowers. Trimeriantha monopolyada gen. et sp. nov. represents the first unequivocal evidence of piperalean flowers from the Late Cretaceous and exhibits a unique combination of floral traits, including a single whorl of tepals, three whorls of stamens, anthers with a single pollen polyad per pollen sac and valvate dehiscence, a fusion of androecium and gynoecium, and an extragynoecial compitum. This trait combination distinguishes it from other extant and fossil angiosperms and further expands our understanding of Cretaceous flower diversity. Our study adds to the extraordinary morphological diversity known from the Late Cretaceous record of flowers, and we discuss some of the floral traits of T. monopolyada with respect to their phylogenetic significance and potential function in pollination biology.