Reinterpretation of fossil reproductive structures Zlivifructus microtriasseris (Normapolles complex, Fagales) from the Czech and Polish Late Cretaceous

Abstract Flowers and fruits of Zlivifructus microtriasseris, originally described as Caryanthus microtriasseris from the late Turonian to Santonian of the South Bohemian Basins and the late Coniacian to early Santonian of the North Sudetic Basin, are reinterpreted here. Zlivifructus microtriasseris is represented by small, flat fruits, round in outline with persistent perianths, which are fused basally, forming the hypanthium. The hypanthium extends for more than two-thirds of the fruit. Tepals leave scars indicating their insertion. Lateral attachment scars of tepals and medial attachment scars are immediately adjacent to each other, with indistinct boundaries forming a ring. The androecium consists of four stamens. The fruit shows the unilocular nature of the nut with a single seed. Lateral faces of the fruit show two parallel ribs or ridges, running from the base of the fruit to the margin of the hypanthium. The surface of the fruit bears irregularly shaped cells. Zlivifructus microtriasseris differs from species assigned to genus Caryanthus Friis 1983 in the presence of four stamen scars, and in having two lateral ribs in the face of the fruit. Zlivifructus microtriasseris differs from the type species Zlivifructus vachae in size of the fruit; shape of the fruit; perianth and attachment scars of tepals. A probabilistic classification method to differentiate between the two fruit species based on their size is proposed.