Floral Evidence of Annonaceae from the Late Cretaceous of Japan
Futabanthus asamigawaensis gen. et sp. nov. is based on a single fossil flower from the Kamikitaba locality in the Ashizawa Formation (Asamigawa Member), Futaba Group (early Coniacian: Late Cretaceous), of northeastern Honshu, Japan. The flower is small, pedicellate, bisexual, and actinomorphic. The floral receptacle is flattened and disk shaped, with a hypogynous perianth consisting of a small number of tepals, borne in at least two cycles, around the rim. The androecium comprises ∼90–100 stamens that are curved toward the center of the flower. Stamens are stout, with no clear differentiation into anther and filament. The thecae are lateral to abaxial in position, extend for most of the length of the stamen, and have latrorse‐extrorse dehiscence. The connective is expanded above the thecae into a prominent, flattened, sterile apical appendage. Together, the connective extensions of the stamens form a tessellated protective surface over the androecium. The gynoecium is composed of ∼100–120 free carpels borne on a small, conical projection in the center of the receptacle. The multipartite construction of the fossil flower, combined with the form of the stamens, indicates a relationship to Annonaceae in the order Magnoliales. The fossil currently provides the earliest record of the family and documents the presence of Annonaceae in eastern Eurasia during the middle part of the Late Cretaceous.